Climate Action and Hydrogen Economy: Technologies Shaping the Energy Transition (Green Energy and Technology) 9819962366, 9789819962365

Table of contents :
Foreword
Preface
About This Book
Contents
Editors and Contributors
Climate Action and Transition to Hydrogen Economy
Green Hydrogen Towards Net Zero
1 Decarbonization—Global Targets
2 India—Decarbonization Strategies
3 Challenge of Green Hydrogen Production
4 Recommended Policy Instruments
5 Conclusions
References
3 ‘Ps’ of Hydrogen Economy in India: Production Pathways, Policies, and Perspectives
1 Introduction
2 For the Hydrogen Economy
2.1 Hydrogen Sources and Production Pathways
3 Hydrogen Storage and Transport
4 End-Use Technologies
5 Policy Landscape in India
6 Perspectives for a Hydrogen Economy in India
7 Conclusions
References
Green Hydrogen: Potential Master Key for Combating Climate Change
1 Introduction
2 Hydrogen Economy and Net-Zero Emissions
2.1 Clean Energy-Based Economy of India
3 Production of Hydrogen
3.1 Production of Green or Renewable Hydrogen
4 Hydrogen Usage and Market Sectors
4.1 Export and Storage of Hydrogen
4.2 Utilization of Hydrogen in Global Market
4.3 Green Hydrogen: Climate-Friendly Energy Solution
4.4 Safety and Regulations
5 Challenges to a Hydrogen Transition
6 Conclusion and Key Takeaway
6.1 Conclusion
6.2 Proposed Initiatives to Make India Global Hub of GH
References
The Net Zero Goal and Sustainability: Significance of Green Hydrogen Economy in Valorization of CO2, Biomass and Plastic Waste into Chemicals and Materials
1 Introduction
2 Hydrogen Production Technologies
2.1 ICT-OEC Green Hydrogen Production Process
3 Green Ammonia
4 Pitfalls of Fossil Carbon-Based Energy Economy
5 Carbon Dioxide as the Future ‘New Oil’
5.1 Flue Gas as Source of CO2
6 Biogas as Source of CO2
7 Biomass Waste as Precursor for Chemicals and Materials
8 Plastic Refining: Chemical Recycling
9 Hydrogenation of Plastic Waste to Valuable Fuels, Monomers and Chemicals
10 Future Direction
11 Conclusions
References
Managing Energy Transition and Challenges of New Energy
1 Introduction
2 World Energy Outlook Report 2022 Key Points
3 Challenges to Reach Net Zero
4 Decarbonisation
5 Solar and Wind Energy
6 Hydrogen as a Fuel for the Future
7 Hydrogen Production
8 Hydrogen Storage
9 Physisorption
10 Chemisorption
11 Challenges on Using Green Hydrogen as a Fuel
12 Transition to Renewables
13 Conclusion
References
STI Policy Push Towards Hydrogen Economy in India
1 Introduction
2 Energy Transition: Historical Perspective
2.1 Air Pollution
2.2 Increasing Fuel Prices and Economic Burden
3 Hydrogen Energy: Leading the Transition
4 Co-evolution of Science, Technology and Innovation Policies and Hydrogen Energy in India
5 Financing Mechanism Towards Hydrogen Energy Transitions
6 Conclusion
References
Sustainability: An Imperative
1 Context of Sustainability: An Evolving View
2 “To Be, or not to Be, that is the Question…” Shakespeare, Hamlet
3 Sustainability and Net Zero: A Framework of Ambitions and Choices
4 Sustainability and Energy Transition: Economic Linkages and Technology Choices
5 Sustainability: Need for an Energy Systems Approach
6 Conclusions
References
Hydrogen Production Technologies
Solar Light-Triggered Hybrid Approaches for Green Hydrogen
1 Introduction
2 Photocatalytic Water Splitting
3 Electrochemical or Photoelectrochemical Water Splitting
4 Photothermal Water Splitting
5 Conclusion
References
Potential for H2 Generation Using 2D-g-C3N4 Nano-Photocatalysts
1 Introduction
2 Experimentally Measured Physicochemical Properties
2.1 Atomic Arrangements
2.2 Chemical Syntheses
2.3 Catalytic Efficiency
2.4 Green Photocatalysis
3 Ab Initio Studies
4 Nanocomposites
5 Discussion and Conclusions
References
Hydrogen Production from Biomass
1 Introduction
2 Hydrogen Production
2.1 Colours of Hydrogen
2.2 Hydrogen Generation Pathways
2.3 Hydrogen from Waste/Biomass—Greener Solution
2.4 Methods to Process Hydrogen from Waste
2.5 Hydrogen from Biomethane Generated from Waste/Biomass
2.6 Advantages of Green Hydrogen from Waste
3 Some Companies in Waste to Hydrogen
4 Typical Cost of Hydrogen from Waste Financial Analysis
5 Policy Recommendations and Implementation Plan
6 Conclusion
References
Green Hydrogen from Biomass Through Gasification—A Carbon Negative Route for Hydrogen Production
1 Introduction
2 Biomass to Hydrogen—The Philosophy
3 Resource Availability
4 Biomass to Gas—Thermochemical Conversion Process
5 Swing Adsorption Process for Pure Bio-hydrogen Generation
6 Gas Characterization for Quality Assessment
7 Fuel Cell Operation with Bio-hydrogen
8 Lab Scale Pilot Plant—A Glimpse and Statistics
9 Conclusion
References
Sustainable Pathways for Hydrogen Production via Molecular Catalysts
1 Introduction
2 Thermal Production of Hydrogen
3 Electrochemical Hydrogen Production
4 Photochemical Hydrogen Production
5 Biological Hydrogen Production
6 Conclusion
References
Hydrogen Production from Liquid Hydrogen Carriers
1 Introduction
2 Liquid Hydrogen Carriers
2.1 Hydrazine
2.2 Formic Acid
2.3 Formaldehyde
2.4 Methanol
2.5 Glycerol
3 Conclusion
References
Solid Oxide Electrolysis Cell for Hydrogen Generation: General Perspective and Mechanism
1 Introduction
1.1 Hydrogen Economy
1.2 Hydrogen Production Technologies
1.3 Mechanism of H2O Electrolysis in O-SOEC and H-SOEC
1.4 Comparison of Proton-Conducting Solid Oxide Electrolysis Cell (H-SOEC) and Oxide-Conducting Solid Oxide Electrolysis Cell (O-SOEC)
2 Materials for H-SOEC and O-SOEC
2.1 Electrolyte Materials
2.2 Air Electrode Materials (Anode)
3 Thermodynamics and Electrochemical Aspects of Electrolysis
3.1 Current–Voltage Characteristics
3.2 Faradaic Efficiency
3.3 H2 Generation Rate
3.4 Durability of SOEC
4 Commercialization/Price Competitiveness of SOEC System
5 Conclusions and Outlook
References
Sustainable Hydrogen Storage
Hydrogen Storage Materials—Background and Significance
1 Introduction
1.1 Energy Priorities: Why Hydrogen as Energy Vector?
2 Physical and Chemical Properties of Hydrogen
3 Hydrogen Storage
4 Interaction of Hydrogen with Solid Surface
4.1 Physisorption of Hydrogen
4.2 Chemisorption of Hydrogen in Metals
5 Hydrogen Storage in Metals and Intermetallics
5.1 Lennard–Jones Potential for the Interaction of Hydrogen with Metals and Intermetallics
6 Kinetics and Thermodynamics of Hydrides
6.1 Kinetics of Hydride During Metal Hydride Formation and Vice Versa
6.2 Thermodynamics and Phase Transformations During Metal Hydride Formation:
7 General Classification of Metal Hydrides
7.1 Intermetallic Metal Hydrides
7.2 AB5-Type Hydrogen Storage Materials
7.3 AB-Type Hydrogen Storage Materials
7.4 AB2 Laves Phases
7.5 BCC Solid Solution
7.6 Lightweight Elemental Hydride
8 Air Stability of Hydrogen Storage Materials
9 Conclusion
References
Prospects of Green Ammonia in Fertilizer Production
1 Introduction
2 Production and Use of Ammonia in India
3 Storage and Transportation of Ammonia
4 Production of Green Ammonia
5 Use of Green Ammonia in Fertilizer Production
6 Implications for Cost of Fertilizers
7 Location of Green Ammonia Plants
8 Conclusion
Reference

Citation preview

Green Energy and Technology

Malti Goel Gautam Sen   Editors

Climate Action and Hydrogen Economy Technologies Shaping the Energy Transition

Green Energy and Technology

Climate change, environmental impact and the limited natural resources urge scientific research and novel technical solutions. The monograph series Green Energy and Technology serves as a publishing platform for scientific and technological approaches to “green”—i.e. environmentally friendly and sustainable—technologies. While a focus lies on energy and power supply, it also covers “green” solutions in industrial engineering and engineering design. Green Energy and Technology addresses researchers, advanced students, technical consultants as well as decision makers in industries and politics. Hence, the level of presentation spans from instructional to highly technical. **Indexed in Scopus**. **Indexed in Ei Compendex**.

Malti Goel · Gautam Sen Editors

Climate Action and Hydrogen Economy Technologies Shaping the Energy Transition

Editors Malti Goel Climate Change Research Institute Delhi, India Former Adviser Ministry of Science & Technology New Delhi, India

Gautam Sen Former Sr VP Reliance Industries and Former ED, ONGC New Delhi, India

ISSN 1865-3529 ISSN 1865-3537 (electronic) Green Energy and Technology ISBN 978-981-99-6236-5 ISBN 978-981-99-6237-2 (eBook) https://doi.org/10.1007/978-981-99-6237-2 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore Paper in this product is recyclable.

Foreword

Hydrogen is being considered a versatile fuel of future as it does not emit any greenhouse gas and could be transported and stored in either gaseous or liquid form. Wider spectrum of usage supporting technologies of low-carbon transition, i.e. ‘green hydrogen’, is indeed a practical solution replacing fossil fuels and reducing dependencies on other conventional and non-conventional resources. The recent launch of the National Green Hydrogen Mission (NGHM) and Niti Aayog’s report ‘Harnessing Green Hydrogen’ released in July 2022 suggests that the demand for hydrogen could grow more than fourfold in the country by 2050. As a part of ongoing celebrations of Azadi Ka Amrit Mahotsav and announcement of Green Hydrogen Policy in early 2022, a three-day awareness workshop on ‘Hydrogen Production and Energy Use: Towards a Net zero Strategy (ACBHPE2022)’ was hosted by the organizers. The workshop was aimed to discuss critical technical issues of hydrogen production, its use, and assessments for the current state of R&D technology considering the nation’s long-term energy future. In the light of above-mentioned background, the book titled ‘Climate Action and Hydrogen Economy: Technologies Shaping the Energy Transition’, Eds: Dr. Malti Goel and Mr. Gautam Sen, contains sixteen chapters based on contributions from v

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leading scientists and technocrats working in the subject domain and also based on the lectures delivered in the workshop held by the Climate Change Research Institute. The content of the book chapters attracts readers on hydrogen energy as a net zero strategy in response to climate change. The book describes advancements in the science and technology of hydrogen production technologies, research perspectives, storage challenges, and energy use in different sectors of the economy. For the ease of readers, the book has three sections with the first one dedicated for the climate action and transition to hydrogen economy. The second section of the book talks about hydrogen production technologies and energy uses, whereas the third section is dedicated to sustainable hydrogen storage. I believe that the present content of the book would be a good edition to on-going global efforts towards this emerging branch of green energy.

Dr. Akhilesh Gupta Secretary, Science & Engineering Research Board (SERB) Senior Adviser Department of Science & Technology Government of India New Delhi, India

Preface

The book Climate Action and Hydrogen Economy: Technologies Shaping the Energy Transition, Eds. Malti Goel and Gautam Sen, an initiative of Climate Change Research Institute for Azadi ka Amrit Mahotsva in the 75th year of India’s Independence, is showcasing the advancements made in the use of hydrogen energy as a move towards Net zero. Energy undoubtedly is at the core of economic progress and human development. There is a direct correlation between a country’s GDP growth and its peoples’ wellbeing with the per capita energy consumed. After the first Industrial Revolution in the mid-eighteenth century, animal and mechanical power gave way to fossil fuel technology. Increased coal mining and, subsequently, oil and gas exploration and exploitation became the order of the day. However, soon it became apparent that burning of fossil fuel resources at this scale can only lead to environmental degradation, making the planet inhabitable. When burnt, fossil fuels produce carbon dioxide, a long-lived greenhouse gas that has a cumulative effect causing global warming and climate change. Fluctuating seasons, extreme weather events, swinging day-to-day temperatures, and heat waves are household manifestations of anthropogenic climate change catastrophes. There are predictions that nature’s fury will affect tropical countries much more. Today, mean global temperature is already crossing 1.1 o C of the pre-industrial level. The Paris Agreement on Climate Change 2015 targets limiting the global temperature increase well below 2 o C suggesting efforts to curb the rise to 1.5 o C. At the current growth rate, climate emergencies threaten the planet’s survival, and the mean global temperature is anticipated to increase up to 2.9 o C or more by the end of the twentyfirst century. The United Nations COP27 meeting held in Sharm-El-Shiekh, Egypt, in 2022 included the ‘Lifestyles for Environment’ mission in its implementation plan and resolves to pursue further efforts to limit the temperature increase to 1.5 °C to achieve the Paris climate goals. Today, the most significant challenge before humanity is managing the energy transition and decarbonizing the energy systems by replacing fossil fuel with low or zero-carbon emitting power. Carbon capture, utilization, and storage (CCUS) is the option for tackling fossil fuel energy emissions, but it is in the demonstration vii

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phase. Significant investments worldwide are taking place in developing renewable resources as 24x7 supplies, and a move towards a hydrogen economy is receiving attention. Hydrogen is emerging as an essential energy source with zero-carbon content and an emission-free source in contrast to fossil fuels, which are majorly responsible for global warming. India held Presidency of the G20 Forum comprising the world’s major economies, including 19 countries and the European Union from Dec. 2022 to Nov. 2023. The G20 New Delhi Leaders’ Declaration stressed on transparent international markets for hydrogen generated from zero or low carbon technologies. The Hydrogen Transition Summit in the United Nations COP28 meeting held from November 30 to December 12, 2023 in Dubai has expressed the need for simplicity, pragmatism and trust in the collaborations, for building the hydrogen economy. The book therefore could not have been published at a more appropriate time. The first announcement of the National Hydrogen Mission (NHM) of India by Prime Minister Mr. Narendra Modi on 15 August 2021 and the Green Hydrogen Policy in February 2022 have substantially increased the interest in realizing the potential for hydrogen energy in the country to play a significant role in the nation’s long-term energy future. The Niti Aayog’s study further pointed out that the demand for hydrogen could grow more than fourfold by 2050. As a result, a growing need for a trained workforce and human resource development will be there.

ACBHPE-2022 In this context, the Climate Change Research Institute (CCRI), founded with a vision to promote climate change education among youth, held a workshop on ‘Awareness and Capacity Building in Hydrogen Production and Energy Use: Towards a Net zero Strategy (ACBHPE-2022)’ on the World Environment Day 2022. The three-day workshop aimed to examine the critical technical issues of hydrogen production, its use, and assessments for the current state of R&D technology with the following objectives: (i) To provide an understanding of the issues and challenges in hydrogen energy towards a Net zero strategy. (ii) To learn about the advancements in science and technology of hydrogen production technologies and energy uses with particular reference to India’s Climate Action and National Hydrogen Mission Initiative. (iii) To put forth perspectives on the transition to hydrogen energy in the knowledge domain and share recommendations with all concerned. The ACBHPE-2022 workshop organized from 8–10 June 2022 in association with the India International Centre and supported by the SERB, Government of India was conducted in ‘hybrid mode’ gave a unique platform for students, teachers, and researchers to share the excitement about on-going developments in hydrogen as an energy carrier in its different facets. Out of twenty-two delegates registered, 15

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participated physically in the three days of deliberations, listening to the dignitaries with a keen interest in learning about the latest developments regarding hydrogen as fuel. Out of these, seven were girl participants. A special session on Start-ups was also held, and 13 companies presented their perspectives. In addition, delegates shared their experience during the workshop.

Structure of the Book The genesis of the book on Climate Action and Hydrogen Economy: Technologies Shaping the Energy Transition is ACBHPE-2022 workshop. It features contributions of leading science luminaries from different academic institutions, research laboratories, and industry stalwarts across the country in its sixteen chapters of particular interest to the readers on hydrogen energy as a Net zero strategy in response to climate change. It covers a wide range of topics related to climate action and hydrogen energy, providing insights into hydrogen production and storage. Gender mainstreaming as a strategy by inviting women to participate as delegates and as contributing authors in the book has been our mainstay. The volume addresses the fundamental issues in its three sections, namely: Part 1 on Climate Action and Transition to Hydrogen Economy deals with climate action, technological pathways in the hydrogen value chain, and the challenges associated with the energy transformation in the different chapters. In addition, policy support needed in developing a roadmap and incentives essential for implementing strategies during the transition period to green hydrogen are deliberated. The need for creative policy instruments, identifying choices in R&D priorities, and holistic system-thinking approach are highlighted. Part 2 on Hydrogen Production Technologies and Uses is about scientific and technological advancements that are taking place globally to produce hydrogen from its various sources and the potential of research and development (R&D) to minimize the costs. Innovations in hydrogen production from water, biomass, liquid hydrogen carriers and advancements made in hybrid approaches, photocatalysis, and molecular catalysis are discussed. An exclusive chapter describes electrolyser development using solid oxide electrolysis cell (SOEC). The technology potential and market competitiveness aspects are touched upon. Part 3 is on Sustainable Hydrogen Storage. Hydrogen in the atomic state is highly reactive, and hydrogen in molecular form could be explosive. Therefore, it must be stored safely and regenerated as and when required. This part covers in detail significant developments in hydrogen storage materials, role of metal hydrides, and perspectives in use of nano-frameworks. A chapter on prospects of green ammonia in the fertilizer industry in India and associated issues is incorporated. A list of participating institutions the is in section Contributing Institutions.

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Acknowledgements The editors acknowledge the renowned leading authors and contributors to the book for their intense engagement, commitment, and hard work. Our sincere thanks are to Prof. D. P. Agrawal Chairman of the Governing Council, for the motivation and leadership. We are deeply indebted to Shri. R. V. Shahi, Former Secretary Ministry of Power, for his inspirational Inaugural address to set the tone of the workshop. He highlighted the policy challenges for introducing hydrogen as a step towards a clean energy transition. Our sincere acknowledgements are due to Padma Shree Prof. G. D. Yadav, National Science Chair, SERB, for his enlightening Keynote address. We profusely thank Dr. V. A. Mendhe, Principal Scientist, CMFRI, Dhanbad, for his enormous support. We acknowledge Dr. P. D. Chavan, Principal Scientist, CMFRI; Prof. S. K. Singh, IIT Indore; Prof. P. C. Ghosh, IIT Mumbai; Dr. Rakesh Kumar, Ex-Director, NEERI; Dr. S. Nand, ADG, Fertiliser Association of India; Prof. G. D. Sharma, Ex-Secretary, UGC; Dr. Bipin Kumar Gupta, Chief Scientist, NPL; Prof. S. Ahmad, Ex-VC, Jamia Hamdard; Ms. Gauri Jauhar, IHS Markit; Shri. R. Varshney, DGM NTPC; Shri. V. S. Verma, Ex-Member, CERC; and Shri. A. K. Jain Ex-Commissioner, Delhi Development Authority for taking part and sharing their wisdom and experience in the workshop about the potential and R&D of hydrogen, which was an eye opener to many delegates. Our special thanks are to Shri Ajay Shankar, Distinguished Fellow, TERI; Dr. Sadhana Rayalu, NEERI Nagpur; Prof. S. Basu, IIT Delhi; Prof. Arnab Datta, IIT Mumbai; Dr. Vandana Maurya, Delhi University; and Prof. S. Dasappa, IISC Bangalore, for their valuable and timely involvement by making a vital contribution to the book. We are thankful to members of GC and EC for their unstinted support and to the staff of CCRI for putting in immense hard work in compiling the data. We express our sincere thanks and appreciation to Ms. Swati Meherishi, Editorial Director, Applied Science and Engineering, Springer Nature. She and her team deserve to be praised for their dynamism and constant help. Especially Ms. Priya Vyas, Senior Editor, and Mr. Ramesh Kumaran, Project Coordinator— Book Production, need mentions for their support and help. We expect this book to be useful for policymakers, students, and professionals and to serve researchers working on national hydrogen missions as a ready reference. It is hoped that this volume would help to reshape the future research in addressing the challenges of the hydrogen economy and making progress towards climate action. New Delhi, India 10 December, 2023

Dr. (Mrs.) Malti Goel Shri. Gautam Sen

About This Book

The Paris Agreement on Climate Change 2015 is a global framework to avoid dangerous climate change by limiting global warming to well below 2 °C and pursuing efforts to limit it to 1.5 °C. The Sustainable Development Goal 13 (SDG13: Climate Action) suggests taking urgent action to combat climate change and its impacts. Attainment of the climate goals would require replacing the use of fossil fuels with the renewable energy sources to minimize greenhouse emissions or no emissions in the atmosphere so as to reach Net zero. Hydrogen molecule as a carbon-free energy carrier is seen to have potential to change the energy dynamics. The book Climate Action and Hydrogen Economy: Technologies Shaping the Energy Transition, Eds: Dr. Malti Goel and Mr. Gautam Sen in its 16 chapters, portrays the promise of Science, Technology and Innovation (STI) in the use of hydrogen as a move towards Net zero strategy. It presents select proceedings of the workshop on Awareness and Capacity Building on Hydrogen Production and Energy Use: Towards a Net zero Strategy (ACBHPE-2022) held in June 2022 and has contributions from the invited top scholars. The book comprises scholarly articles on breakthroughs in science, technology, and policy actions needed across the hydrogen value chain for it to emerge as a tool for climate action.

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Contents

Climate Action and Transition to Hydrogen Economy Green Hydrogen Towards Net Zero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ajay Shankar

3

3 ‘Ps’ of Hydrogen Economy in India: Production Pathways, Policies, and Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Malti Goel

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Green Hydrogen: Potential Master Key for Combating Climate Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shweta Gupta, Ankit Gupta, Hemant Bherwani, and Rakesh Kumar

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The Net Zero Goal and Sustainability: Significance of Green Hydrogen Economy in Valorization of CO2 , Biomass and Plastic Waste into Chemicals and Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ganapati D. Yadav Managing Energy Transition and Challenges of New Energy . . . . . . . . . . Gautam Sen

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STI Policy Push Towards Hydrogen Economy in India . . . . . . . . . . . . . . . . 107 Vandana Maurya, Paramita Ghosh, and Anshuman Gunawat Sustainability: An Imperative . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 Gauri Jauhar Hydrogen Production Technologies Solar Light-Triggered Hybrid Approaches for Green Hydrogen . . . . . . . . 127 Girivyankatesh Hippargi and Sadhana Rayalu Potential for H2 Generation Using 2D-g-C3 N4 Nano-Photocatalysts . . . . 139 A. Nazeer, F. Ahmad, and S. Ahmad

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Contents

Hydrogen Production from Biomass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 Rajan Varshney Green Hydrogen from Biomass Through Gasification—A Carbon Negative Route for Hydrogen Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 S. Dasappa, Anand M. Shivapuji, and Mishma S. Stanislaus Sustainable Pathways for Hydrogen Production via Molecular Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 Mahendra Kumar Awasthi, Surabhi Rai, and Arnab Dutta Hydrogen Production from Liquid Hydrogen Carriers . . . . . . . . . . . . . . . . 213 Sanjay Kumar Singh Solid Oxide Electrolysis Cell for Hydrogen Generation: General Perspective and Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 Subhrajyoti Ghosh and Suddhasatwa Basu Sustainable Hydrogen Storage Hydrogen Storage Materials—Background and Significance . . . . . . . . . . . 263 Ashish Bhatnagar and Bipin K. Gupta Prospects of Green Ammonia in Fertilizer Production . . . . . . . . . . . . . . . . 303 Sachchida Nand and Manish Goswami

Editors and Contributors

About the Editors Dr. (Mrs.) Malti Goel is former Adviser and Scientist ‘G’ and CSIR Emeritus Scientist in the Ministry of Science and Technology, Government of India. She received her Ph.D. (Physics) and D.I.I.T. (Solid State Physics) degree in First Position with Distinction from the Indian Institute of Technology (IIT), Delhi; M.Sc. (Physics) from Birla Institute of Technology and Science (BITS), Pilani, with the first rank receiving a Gold Medal in 1967. She has professionally distiguished in scientific research, policy planning, and in creating an impact on the national scene by capacity building in climate change mitigation through application of science and technology. As a prolific science writer, she has 14 books and over 300 publications to her credit in the form of research articles in peer-reviewed journals, and papers in conference proceedings. She has won many awards and honours. For her outstanding contribution to climate change education and research in India, she received ‘Life Time Achievement Award’ in the year 2016 by the Pearl Foundation Madurai. She is Recipient of IITDAA ‘Outstanding Contribution to National Development (OCND)’ award in the year 2023.

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Editors and Contributors

Shri. Gautam Sen joined the Oil and Natural Gas Commission in 1976, which later became Corporation, after completing his Master’s degree in Physics from Delhi University. He worked as Geophysicist and then as Oil and Gas Explorationist in both onshore shallow waters and deep water offshore and in their institutes for over three decades. He rose to the level of Executive Director and served at this level for six years. He later joined RIL as Senior Vice President in the Exploration of Oil and Gas. He was Technical Head for all explorationrelated matters, and RIL’s blocks were mainly in deep waters in the east coast of India. After superannuation, he has been Consultant in oil and gas in both private and public sectors. He has a large number of publications and is also a recipient of the National Mineral award from the Government of India.

Contributors F. Ahmad Faridabad, Haryana, India S. Ahmad Faridabad, Haryana, India Mahendra Kumar Awasthi Chemistry Department, Indian Institute of Technology Bombay, Powai, Mumbai, India Suddhasatwa Basu Department of Chemical Engineering, Indian Institute of Technology, Delhi, India Ashish Bhatnagar Department of Physics and Materials Science and Engineering, Jaypee Institute of Information Technology, Noida, India Hemant Bherwani CSIR-National Environmental Engineering Research Institute, CSIR-NEERI, Nagpur, India S. Dasappa Interdisciplinary Centre for Energy Research, Indian Institute of Science, Bangalore, Karnataka, India Arnab Dutta Chemistry Department, Indian Institute of Technology Bombay, Powai, Mumbai, India; National Centre of Excellence in CCU, Indian Institute of Technology Bombay, Powai, Mumbai, India; Interdisciplinary Program in Climate Studies, Indian Institute of Technology Bombay, Powai, Mumbai, India Paramita Ghosh Motilal Nehru College, University of Delhi, New Delhi, India

Editors and Contributors

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Subhrajyoti Ghosh Department of Chemical Engineering, Indian Institute of Technology, Delhi, India Malti Goel Climate Change Research Institute, Delhi, India; Department of Science and Technology, Ministry of Science and Technology, New Delhi, India Manish Goswami The Fertiliser Association of India, New Delhi, India Anshuman Gunawat Motilal Nehru College, University of Delhi, New Delhi, India Ankit Gupta CSIR-National Environmental Engineering Research Institute, CSIRNEERI, Nagpur, India Bipin K. Gupta CSIR-National Physical Laboratory, New Delhi, India Shweta Gupta CSIR-National Environmental Engineering Research Institute, CSIR-NEERI, Nagpur, India Girivyankatesh Hippargi Environmental Materials Division, CSIR-National Environmental Engineering Research Institute, Nagpur, India Gauri Jauhar Energy Transitions and Clean Tech Consulting, S&P Global, Gurugram, India Rakesh Kumar Council of Scientific and Industrial Research (CSIR), New Delhi, India Vandana Maurya Motilal Nehru College, University of Delhi, New Delhi, India Sachchida Nand The Fertiliser Association of India, New Delhi, India A. Nazeer Faridabad, Haryana, India Surabhi Rai Chemistry Department, Indian Institute of Technology Bombay, Powai, Mumbai, India; National Centre of Excellence in CCU, Indian Institute of Technology Bombay, Powai, Mumbai, India Sadhana Rayalu Environmental Materials Division, CSIR-National Environmental Engineering Research Institute, Nagpur, India Gautam Sen Former Executive Director, Oil and Natural Gas Corporation, Senior Vice President RIL (E and P), New Delhi, India Ajay Shankar The Energy and Resources Institute, New Delhi, India Anand M. Shivapuji Interdisciplinary Centre for Energy Research, Indian Institute of Science, Bangalore, Karnataka, India Sanjay Kumar Singh Catalysis Group, Department of Chemistry, Indian Institute of Technology Indore, Indore, M.P., India

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Editors and Contributors

Mishma S. Stanislaus Interdisciplinary Centre for Energy Research, Indian Institute of Science, Bangalore, Karnataka, India Rajan Varshney Delhi, India Ganapati D. Yadav Emeritus Professor of Eminence and National Science Chair (SERB/DST/GOI), Institute of Chemical Technology, Mumbai, India

Climate Action and Transition to Hydrogen Economy

Green Hydrogen Towards Net Zero Ajay Shankar

Abstract Achieving net zero at the earliest is essential for the survival of mankind. The latest IPCC reports make it clear that time is running out. With present trends global warming is set to not only cross 1.5° considered essential by science, but to go well over 4° by 2100. This would make the planet uninhabitable. The sanguine confidence in some quarters that either the science is wrong, or, that technology would achieve some miraculous breakthrough in carbon capture that would enable us to continue using fossil fuels without adding to carbon emissions and global warming is delusional. Immediate course correction for rapid decarbonization on a massive scale is required if there is to be any hope. : Learning objectives • Decarbonization strategies—global and India • Green hydrogen challenges in India • Suggested policy actions for achieving the goal Keywords Decarbonization · Green hydrogen · Strategies & challenges · Policy instruments

1 Decarbonization—Global Targets Decarbonization needs to be brought forward rather than being back ended as has been the approach till now. The advanced economies and many other nations have set the goal of becoming net zero by 2050. This goal needs to be brought forward to, say, 2040 with the bulk of decarbonization being undertaken over the next 10–15 years. This is imperative. The full decarbonization of electricity is now technically feasible. The share of renewables in electricity has crossed 46% in a large economy like Germany. The share of variable renewable energy in Germany electricity rose from A. Shankar (B) The Energy and Resources Institute, New Delhi, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Goel and G. Sen (eds.), Climate Action and Hydrogen Economy, Green Energy and Technology, https://doi.org/10.1007/978-981-99-6237-2_1

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...in 2000 to over 45% in 2020 [1]. Using renewables with storage for decarbonizing electricity is the way forward. The cost of renewable electricity, solar and wind is far lower than that of electricity from any other source. The cost of storage has also come down rapidly. The transition to carbon-free electricity is doable and affordable. The way gas prices went up due to the conflict in Ukraine made electricity from renewables with storage relatively cheaper and made the case for phasing out all fossil fuel-based electricity generation that much stronger. Only the will in governments is needed. California has set 2045 as the year for having carbon-free electricity. President Biden in his election campaign had promised a carbon free electricity system in America by 2035. All the advanced industrial economies could create carbon free electricity systems by 2035 if they acted on a war footing. Civil society and public opinion need to put pressure on their governments and give them the political will not to yield to the power and influence of the fossil fuel industry whose interests lie in delaying effective action as long as possible. In parallel and to the extent it is technically feasible, economic activity needs to be electrified. As electricity gets decarbonized, these segments of our economies would also get decarbonized. We are already seeing substantial progress. Electric vehicles are rapidly gaining market share. UK had decided that automobiles using fossil fuels would not be sold after 2030 [2]. EU and California intend to have a similar prohibition coming into effect in 2035. The Indian Railways are completing the transition to using electricity for carrying goods and passengers. They are aiming to become net zero by 2030 [3]. Many countries use only electricity for cooking. India needs to encourage and incentivize the use of electricity and biogas, a renewable source of energy, for cooking and develop a road map for doing away with the use of LPG and natural gas for cooking. Those who use oil and gas for heating in cold climates need to switch to using electricity instead. Governments in these countries have been too slow and need to give this higher priority. There are parallel transitions which should take place. First, electrification of vehicular transport, two and three wheelers, cars, buses, trucks on the one hand and the Railways on the other. Switching over to electricity for residential heating in cold countries and substitution of fossil fuels by electricity in industrial processes to the extent it is technically feasible need to happen in tandem. All these combined by rapid decarbonization of electricity should result in the elimination of a major part of total carbon emissions in the world. But there are large parts of the economy which cannot be electrified. There are many industrial processes where electricity cannot replace fossil fuels. Long distance shipping and civil aviation cannot be electrified. In all such sectors, called ‘hard to abate sectors’, green hydrogen has emerged as a potential substitute for fossil fuels. Green hydrogen means hydrogen produced without the use of fossil fuels. Hydrogen cars, heavy duty trucks and trains have already been developed. Substitution in many industrial processes seems possible. This transition is, however, at a very early stage, and it is recognized that this needs to be accelerated for the achievement of net zero. All the advanced industrial economies are aiming to become leaders in the new Hydrogen Economy. Their governments are supporting their firms along with their technical institutions to gain the lead and resultant competitive advantage. India is

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joining the advanced industrial economies in aiming to reach the global frontier in this critical sunrise sector.

2 India—Decarbonization Strategies Hydrogen made from natural gas, called grey hydrogen, has been in use in some industrial processes. In India it has been in use in the production of ammonia for fertilizer production. But for hydrogen to be a substitute for fossil fuels it must be green hydrogen which must be produced without using fossil fuels. The production of green hydrogen on industrial scale is done through electrolysis of water using carbon-free electricity. India can use seawater along its vast coastline for producing green hydrogen without using scarce freshwater. The carbon-free electricity can come from renewables, renewables with storage and nuclear power. The main costs in the production of green hydrogen are the cost of electricity and of the electrolysers. The cost of electricity from renewables has fallen dramatically. The cost of electrolysers is also falling with innovation triggered by competition and the expectation of huge demand. While it is not possible to predict how much cost reduction can be achieved, the expectation of cost reduction is not unrealistic. Hydrogen can also be made from bio waste. As bio waste is a renewable resource, hydrogen made from it should legitimately be considered as green hydrogen. We should do so and also try for global acceptance of this. India by launching its Green Hydrogen Mission is joining the advanced countries in pursuing the production of green hydrogen and its downstream uses especially in the hard to abate sectors [4]. This would place India on the global frontier. It would make the transition to becoming energy independent by 2047 and becoming net zero feasible. The National Green Hydrogen Mission reflects our confidence that we can aim to be on the global frontier along with the advanced industrial economies in this critical area [5]. The Mission aims at achieving India’s potential to becoming a leading producer, user and exporter of green hydrogen. The recently released Mission document is bold and comprehensive. It covers the whole value chain from production to storage and transportation to all feasible downstream uses. Production of 5 MMT of green hydrogen by 2030 for domestic use along with an additional 5 MMT for exports is envisaged. The intention is to create demand for downstream use in manufacturing of fertilizer, steel and chemicals, and in transport in heavy duty trucks and shipping. Financing of over Rs. 19,000 crores has been committed. It also sets out the responsibilities of the other ministries as well as the coordination process and the mechanism for taking decisions through the Empowered Group chaired by the Cabinet Secretary. It accepts the need of leadership from government as well as financial support.

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3 Challenge of Green Hydrogen Production Implementation of such an ambitious vision in a sunrise frontier technology area would be a formidable task. The challenge would be to create in partnership with industry and technical institutions pathways for success in each segment to reach the global frontier. This is not going to be easy. It would require continuing success in technology absorption, innovation and movement down the cost curve with the requisite scale and competition. We live in a globalized world and should get the best technologies at the going market rates. There is usually no point in trying to reinvent the wheel. We should be able to produce at globally comparable costs and then try and innovate to improve on technology and lower the cost of production further. We may succeed and to the extent we do we would become a globally competitive production centre in the new Hydrogen Economy. These difficult policy goals have to be pursued at the least cost to the public exchequer. India will continue to face fiscal constraints in the coming years. Nevertheless, sustained leadership from government would be necessary to improve the likelihood of success. The right policies and programs backed by fiscal and other measures would be the key. Creating a competitive industry structure in the new hydrogen economy would help in moving down the cost curve. This has been seen in the success of the Solar Mission. A good beginning has been made with the production of green hydrogen. There are ambitious plans announced by our leading firms to become globally competitive producers of green hydrogen within this decade. We are well placed to do so as we have the cheapest costs of electricity from renewables. We can also try and become the cheapest producers of electrolysers needed for producing green hydrogen. A start-up has already started producing and exporting green hydrogen from India.

4 Recommended Policy Instruments The major task would be to initiate projects for each potential downstream use. This can be done by using any, or, a mix of the policy instruments available to government. These instruments are as follows. (a) Government buying green steel on a continuing basis for its building projects though it would be more expensive. The government can absorb the higher cost of steel whose impact on the final cost of the building would be marginal. This would not need any upfront subsidy from the budget [6]. (b) lower GST rates-being used to promote electric vehicles. (c) subsidy per unit of production as is being done for fertilizers, where the sale price is fixed and the difference between this and the cost of production is given as a subsidy to the fertilizer producing units. (d) interest subsidy on debt, (e) capital subsidy as has been done as Viability Gap Funding, for infrastructure projects and

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(f) Production Linked Incentive (PLI) to offset the higher cost of production for the initial few years. Transportation and storage of hydrogen need specialized materials. The Mission envisages blending of green hydrogen with gas in city gas distribution. But in the long-run use of gas has to end if we are to reach net zero. Existing pipelines for gas may be amenable with additional investment and retrofitting to become carriers for green hydrogen. This could be a cheaper option than laying fresh pipelines. Tankers for carrying hydrogen also need to be developed. If with cost reduction, heavy duty trucks using green hydrogen become cost competitive, then hydrogen filling stations would be needed on our highways. Pilot projects undertaken now on filling stations and running hydrogen trucks would create the capacities for the rapid installation of hydrogen filling stations on the highways. Initial learning would create capacities for cost reduction with scale and volumes. As the production of green hydrogen begins, ensuring that demand for downstream uses is created to match production would be essential. In comparison with designing a Production Linked Incentive (PLI) Scheme for a mature product in an existing market, such as mobile phones, the task here is more complicated as domestic demand for green hydrogen must be created. How to do so while minimizing the need for budgetary support? Can other instruments be devised for the same outcomes? One way would be to go in for competitive procurement, create a competitive industry structure so that movement down the cost curve is accelerated through successive bids enabling India to also get the full benefit of the global decline in prices that are likely. This approach was successful in the National Solar Mission when the price of solar power was initially about four times the price of thermal power and has now become clearly much cheaper. For the Hydrogen Mission, the minimum size of plants for least cost production would need to be determined for the production of green hydrogen and its downstream uses at the outset. The minimum economic size of a new fertilizer plant, a green ammonia manufacturing unit and a green hydrogen producing plant would need to be ascertained along with the cost. Then working backwards from the fertilizer plant, supply and demand of green ammonia and green hydrogen would have to be matched for the supply chain. Competitive bids may be invited to get the least cost of production of green hydrogen. With this green hydrogen cost, the price of green ammonia may be competitively determined. This input price would then become the basis for inviting bids for production of green fertilizer. Subsidy from the budget for each ton of green fertilizer produced may then be given to bridge the gap between the market determined price of green fertilizer and the price fixed by government for sale to farmers. This subsidy would naturally be far higher than the subsidy being given per ton for normal fertilizer production. No subsidy would, however, be needed for the intermediate stages. Similarly, government could enter a long-term procurement contract for the entire production of a green steel plant. As this would be one of the first green steel plants in the world, our major steel producers should be persuaded to form a consortium and set up the plant so that they all learn the new technology. The purchase price would

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then have to be on a cost plus basis. It would also be necessary to accept at the outset that cost and time overruns could occur and price escalation may become necessary. This more expensive steel may be used by government in all its own construction projects as well as of its agencies. The impact on the final cost per square meter would be marginal and could be easily absorbed by the budgets of the construction projects. No direct subsidy would be needed. After the success of the first plant in proving the technology, setting up other plants by all the steel producers may be promoted competitively. This would hasten movement down the cost curve [7]. At some time in the future government could consider prohibiting the setting up of any new steel plant that uses fossil fuels. For shipping, the supply chain up to green ammonia would be the same as for fertilizer production. Competitive procurement of green shipping services from a reasonable future date could be done through a long-term contract indicating the price at which green ammonia would be supplied. This would completely de risk the investment in building a cargo ship that would use green ammonia. The higher cost of the shipping service can easily be absorbed by the Indian user as freight costs are a small portion of his total cost. In this case again, subsidy would not be needed. For the market-based competitive chemical, pharma and other industries, use of green hydrogen could be promoted by making its cost comparable to the fuel it would replace, and this could be done by a combination of a lower GST rate as has been done for electric vehicles (EVs), and a direct subsidy per kg of green hydrogen used [8]. This would also need to be done for the use of green ammonia for electricity generation for meeting seasonal spikes in electricity demand. However, storage and transport of hydrogen have high costs. Pilots projects with competitive procurement would create capacities which could later be scaled up with cost reduction. Each of these would need separate sub-missions in the concerned sectors. Difficult decisions on the policy instruments to be used, selection of industry partners and extent and manner of financial support to be provided would need to be taken speedily. Policy consistency and predictability is what private partners expect. If changes are considered necessary as they may be at times, transparent stakeholder consultations should be undertaken beforehand. Separate funding for sharply defined and focussed technology and product development where improvement in performance parameters or cost reduction seems feasible may be attempted in challenge mode with competitive consortia being invited. The successful DARPA model for defence technology innovation of the USA may be adapted for this Mission. This would need nimble technical leadership and a speedy decision-making process. This is not easy. There is a strong case for special empowerment for implementation of the Hydrogen Mission by way of being able to choose partners on selection rather than only through tendering were considered necessary. In these cases, funding would also need to be decided on a case-to-case basis. It would also be essential to accept at the outset that there is real risk of failure as well as time and cost overrun in this frontier technology area.

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5 Conclusions Our large fossil fuel companies in the public as well as the private sector need to accept the inevitability of the energy transition. They can choose to move swiftly and competitively into the new green energy economy, succeed and grow. They have deep pockets and enormous technical and managerial talent. They, however, need to get out of their comfort zone and embrace transformation with zeal and confidence. Or they should be prepared to disappear. The choice is stark. Recent examples of disappearance of Kodak and Blackberry are illustrative. In the government various ministries and the empowered groups under the Chairmanship of the Cabinet Secretary need to now look in depth at where we would like to be at the end of the decade in downstream uses of green hydrogen, and then backwards on what needs to be done and how and with what fiscal support. Setting out the complete goal of production and sector wise usage with projected supply matching demand would be the right way to move forward. The concerned ministries need to collectively create demand which matches the production of green hydrogen. With creative policy instruments used with speed, flexibility and agility, we could be at the global frontier in this decade and that too at affordable costs. The potential for this is high due to the abundance of young talent with ambition in India.

References 1. https://www.sciencedirect.com/science/article/pii/S0360544222002067 2. https://www.gov.uk/government/news/government-takes-historic-step-towards-net-zero-withend-of-sale-of-new-petrol-and-diesel-cars-by-2030 3. Press Information Bureau (pib.gov.in), Indian Railways to become net zero by 2030. 4. Press Information Bureau (pib.gov.in), Cabinet approves Green Hydrogen Mission. 5. National Hydrogen Mission: Decarbonising India, Achieving Net-Zero Vision, Ministry of New & Renewable Energy, Government of India, March 21, 2022 https://static.pib.gov.in/Wri teReadData/specificdocs/documents/2023/jan/doc2023110150801.pdf. 6. Harnessing Green Hydrogen: Opportunities for Deep Decarbonization in India, Niti Aayog, June 2022. 7. Can Industry Decarbonize Steelmaking? Chemical & Engineering News, 2021. 8. Press Information Bureau (pib.gov.in).

3 ‘Ps’ of Hydrogen Economy in India: Production Pathways, Policies, and Perspectives Malti Goel

Abstract Hydrogen production technologies are getting a new thrust with planetary emergencies like climate change. It is anticipated that hydrogen electricity in the long run may become more economical than fossil fuel-based electricity with carbon capture and storage, leading to a move towards the hydrogen economy. A hydrogen economy would provide long-term industrial sustainability compared to the intermittent energy harnessed from renewable resources. Hydrogen, being the first element of the Periodic Table, is the lightest and smallest, abundant in the universe, yet it is not found as a free molecule in the atmosphere. Highly chemically reactive, it is present in many chemicals around us, from water and hydrocarbons to polymers and plastics and many others, including living systems like plants and animals. Which is the best source for producing hydrogen? has been a dilemma for a long time. India, in the 26th meeting of the Conference of Parties (COP26) of the United Nations Framework Convention on Climate Change held in Glasgow, has committed to reducing its GHG emissions by 45% by 2030 and to becoming carbon neutral by 2070 with a Panchamrit action plan to achieve green transformation with accelerated climate action. In a move towards a net zero strategy, significant steps have been taken to promote green hydrogen development. In the 75th year of India’s independence, an ambitious goal of making India a global hub and achieving green hydrogen production of 5 MTPA by 2030 has been stated. This chapter gives an overview of different sources of hydrogen, methods, and technologies of the hydrogen value chain. It describes the policy landscape in India and the opportunity it presents for a hydrogen economy in India. Learning objectives: • • • •

Natural and anthropogenic sources of hydrogen Technologies in the hydrogen value chain Policy landscape in India Perspectives for the hydrogen economy in India

M. Goel (B) Climate Change Research Institute, Delhi, India e-mail: [email protected] Department of Science and Technology, Ministry of Science and Technology, New Delhi, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Goel and G. Sen (eds.), Climate Action and Hydrogen Economy, Green Energy and Technology, https://doi.org/10.1007/978-981-99-6237-2_2

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Keywords Climate action · Hydrogen sources · Production pathways · Policies in India · Perspectives

Abbreviations AEM BHEL BPCL CCUS COP GHG GIFT GIP GAIL HESC HCF HPCL IEA ICE ITER ITSE IOCL ISRO MCFC NAPCC NDC NGHM NTPC ONGC PEM PCEC PLI RIL SOEC SIGHT UNFCCC VPSA

Anion Exchange Membrane Bharat Heavy Electricals Limited Bharat Petroleum Corporation Limited Carbon capture, utilization and storage Conference of Parties Greenhouse gas Green Initiative for Future Transport Green Initiative for Power Gas Authority India Ltd. Hydrogen Energy Supply Chain Hydrogen Corpus Fund Hindustan Petroleum Corporation Limited International Energy Agency Internal Combustion Engine International Thermonuclear Experimental Reactor Intermediate Temperature Steam Electrolyser Indian Oil Corporation Limited Indian Space Research Organization Molten Carbonate Fuel Cell National Action Plan on Climate Change Nationally Determined Contribution National Green Hydrogen Mission National Thermal Power Corporation Oil & Natural Gas Corporation Proton Exchange Membrane Proton Ceramic Electrolyser Cell Production-linked incentive Reliance Industries Ltd Solid Oxide Electrolyser Cell Strategic Interventions for Green Hydrogen Transition United Nations Framework Convention on Climate Change Vacuum pressure swing adsorption

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1 Introduction The 2030 Agenda for Sustainable Development has 17 sustainable development goals (SDGs), adopted by the United Nations in 2015. It calls for making necessary changes in the current pattern of growth to end poverty, protect the planet from climate change, and ensure that by 2030 all people enjoy peace and prosperity. The climate change menaces are becoming real threats to the survival of the planet earth. Fluctuating seasons, extreme weather events, swinging day-to-day temperatures, and heat waves are household manifestations of anthropogenic climate change, causing devastation and havoc to human health. There are predictions that nature’s fury will affect tropical countries much more. The Climate Action: SDG13, demands multiple actions for achieving sustainability by rapid decarbonization of economies. The Paris Agreement on Climate Change targets limiting the global temperature increase to well below 2 °C and suggests further restricting the rise to 1.5 °C. But both of these seem not feasible at the current rate of growth. Global temperature has already increased 1.1 °C from the pre-industrial era. At the current growth rate, the global temperature may increase by 2.9 °C near the end of the century. In this context, the Conference of Parties (COPs) of the United Nations Framework Convention on Climate Change (UNFCCC) meet to discuss and urge the member countries to take control of global climate change. The UNFCCC is the international treaty evoked in 1992, at the Earth Summit held at Rio-de-Janeiro, Brazil. It was agreed that although current assessments for temperature rise were uncertain in the 1990s, the reduction in harmful greenhouse gas emissions from fossil fuel use must be curtailed in the long run. The science of global warming, however implies that the long-lived greenhouse gases (GHGs) in the atmosphere would not respond immediately to the emission cuts. After the first 50 countries ratified the Convention by 1994, negotiations began among the developed and developing country Parties. Since then, the COP’s meetings have been held annually (except for the COVID-19 pandemic year 2020), registering national progress and negotiating future climate actions by the parties. In 2021, the 26th meeting of COPs has driven a move towards net zero emissions and taken accelerated steps towards decarbonization. In the meeting, big economies pledged to achieve net zero targets by 2050, while India proposed 2070 and China gave a target of 2060. The COP27 meeting in 2022 held at Sharm-El-Shiekh, Egypt, affirmed and it was agreed to set the limit on global temperature rise to 1.5 °C. The Intergovernmental Panel on Climate Change (IPCC) 6th Assessment report projections for global surface temperature changes in degrees Celsius relative to 1850–1900 under the five core emissions scenarios, are shown in Fig. 1 [1]. It suggests warming is ‘very likely’ to be 1.0–1.8 °C by 2081–2100 in the lowest emissions SSP1–1.9 scenario, 2.1–3.5 °C in the intermediate SSP2–4.5 scenario, and 3.3– 5.7 °C under the SSP5–8.5 high emission scenario. In the lowest emissions scenario SSP1–1.9 (light blue line), temperature reach 1.4 °C above 1850–1900 levels in 2081–2100, whereas it climbs 4.4 °C under SSP5–8.5 (dark red line).

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Fig. 1 Global surface temperature changes relative to 1850–1900, degrees Celsius, under the five core emissions scenarios used in AR6. Source IPCC (2021)

The energy sector contributed up to 70% of CO2 emissions, resulting in megatrends in energy transition for climate change mitigation [2]. We can take action towards low-carbon development through education, science, technology, and innovation. To reduce CO2 concentrations in the atmosphere the ways are; a. A shift towards renewable energy or carbon-free sources such as hydrogen for generation of electricity b. Enhancement of energy efficiency in processes and products c. Decarbonization of electricity from fossil fuels by carbon capture, utilization and storage d. Technology innovations for low-carbon development e. Increasing natural carbon sinks through agriculture management practices and forestation.

2 For the Hydrogen Economy The IPCC report for policymakers has stated, ‘If the world is to reach net zero emissions, hydrogen will play a vital role’. Hydrogen is a carbon-free clean energy fuel. Therefore, a hydrogen-based economy can make a significant impact. Hydrogen, discovered in 1766, its production from water electrolysis was demonstrated in 1789 by passing current to produce hydrogen and oxygen. A science fiction author, Jules Verne, built a story in 1874 ‘Mysterious Island’ and wrote ‘Water will one day be employed as fuel, that hydrogen and oxygen which constitute it, used singly or together, will furnish an inexhaustible source of heat and light, of an intensity of which coal is not capable’ [3]. His characters flew in a balloon filled with hydrogen. Fifty years later, a hydrogen-filled airship took off in 1934. As a maiden step towards a hydrogen economy, the first commercial trans-Atlantic flight was operated in 1936. However, the airship met with an accident a year later that came to be known as the Hindenburg disaster [4]. After that, hydrogen use in the liquefied form had mainly confined to space shuttles for several years. Other uses of hydrogen developed and key breakthroughs from 1766 onwards are depicted in Table 1.

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Table 1 Hydrogen use development Year Hydrogen discoveries and advancements in use of hydrogen 1766 Hydrogen element was discovered by Henry Cavendish, a British scientist. 1783 Antoine Lavoisier, a French scientist gave hydrogen its name. 1789 Electrolysis of water was demonstrated by passing current to produce hydrogen and oxygen gases. 1838 The ‘Fuel cell effect’ combining hydrogen and oxygen gases to produce electric current was invented by Sir William Groove, a Welsch physicist. 1888 First industrial water electrolyser was developed. 1937 The hydrogen gas-filled airship in a trans-Atlantic flight from Germany to the USA crashed upon landing. (This had put a halt to the use of hydrogen in air transport) 1959 First industrial application of a 5-kW fuel cell to power a welding machine was demonstrated. 1966 First hydrogen cell Chevrolet Electrovan commercial hydrogen vehicle was introduced with a hydrogen tank. 1970 John Bockris coined the term hydrogen economy at a General Motors Technical Center. 1973 The OPEC oil embargo and oil shock led to the development of hydrogen fuel cells as an alternate source of energy. 1973 A 30-km hydrogen pipeline was built in Isbergues, France. 1975 First book titled ‘Energy: The Solar-Hydrogen Alternative’ by John O’M Bockris, ISBN 0–470-08,429-4 was published. 1988 Use of liquid hydrogen in a commercial jet was demonstrated by the Soviet Union. 1994 Daimler Benz, Germany, demonstrates New Electric Car (NECAR) fuel cell vehicle. 1997

NASA scientist claimed that Hindenburg accident was not caused by hydrogen.

1998 Iceland unveiled a plan to create the first hydrogen economy by 2030. 1999 First hydrogen filling station for vehicles came up in Germany. 2001 The first type-IV hydrogen tanks for compressed hydrogen at 700 bar (10,000 PSI) were demonstrated. 2003 US President George W. Bush announced a $1.2 billion hydrogen fuel initiative. 2004 World’s first hydrogen fuel cell-powered submarine, DeepC was tested in deep waters. 2004 India set up a National Hydrogen Energy Board to examine its production from different sources. 2016 Toyota releases its first hydrogen fuel cell car, named the Mirai (Japanese for future). 2017 METI Japan issued the Basic Hydrogen Strategy, world’s first national strategy to build a hydrogen society. In 2022, Japan has unveiled its National Hydrogen Strategy, with the aim of building a H2 supply chain to produce 8,00,000 H2 fuel cell vehicles by 2030. 2017 Hydrogen Council was formed to expedite the development and commercialization of hydrogen and fuel cell technologies. 2020 EU establishes its hydrogen strategy for a climate neutral Europe with a mandate that 45% of all new buses be zero emission, and the percentage will increase to 65% from 2025 onwards. 2021 Sunlight-driven hydrogen production using floating artificial leaves technology was demonstrated. (continued)

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Table 1 (continued) Year Hydrogen discoveries and advancements in use of hydrogen 2021 India launched the National Hydrogen Mission. 2022 The US passed an infrastructure bill aiming to invest $8 billion in creating four hydrogen hubs to produce, store, and use, with at least one for blue hydrogen and one for green hydrogen. 2023 India announced the National Green Hydrogen Mission with a budget of approx. 20,000 crores INR to make India a global hub for green hydrogen. Compiled by Author, using information from various sources

Derek P. Gregory, on 1 January 1973 issue of Scientific American, a popular science journal in the USA, made a case for ‘The Hydrogen Economy’ in which all energy sources would be used to produce hydrogen, a non-polluting multipurpose fuel for multi-sectoral uses [5]. The impending oil crisis was the prime concern then. The International Journal of Hydrogen Energy was established in 1976 as a peerreviewed scientific journal covering all aspects of hydrogen energy R&D, including hydrogen generation and storage. The US National Research Council had appointed a Committee on ‘Alternatives and Strategies for Future Hydrogen Production and Use’ in 2002. A transition to hydrogen as a primary fuel in the next 50 years was central for giving policy support to energy security and improved environmental quality, including CO2 emissions reduction. Detailed recommendations included enhanced budget in three areas, namely (i) research and development (R&D) priorities, (ii) the challenge of the energy transition, and (iii) hydrogen use in vehicles [6]. The US Government announced a $1.2 billion hydrogen fuel initiative. The Japan developed its Strategic Roadmap for Hydrogen and Fuel Cells and issued the Basic Hydrogen Strategy in 2017, becoming the first country with a goal to create a hydrogen society [7]. Japan’s Hydrogen Strategy aimed to build an H2 supply chain targeting 800,000 fuel cell cars and 1200 fuel cell buses by 2030. The European Union (EU) legislation has mandated that from 2021 onwards, 45% of all buses must be zero emission vehicles, which is to increase to 65% from 2025 onwards. To give industrial thrust to hydrogen development, the World Economic Forum in Davos took the initiative and 13 industries formed the ‘Hydrogen Council’ in 2017 to collectively strive for a successful transition to a low-carbon society [8]. In 2022, the number had grown to nearly 150 members. According to the Hydrogen Council, hydrogen can unlock 15% of global energy demand by 2030. Post COVID-19, major economies of the world have their hydrogen strategies in place. The hydrogen economy to attain a long-term industrial sustainability [9] has the following three broad ingredients: (i) large-scale hydrogen production, (ii) safe storage and distribution, and (iii) its use in the hard-to-abate sectors of the economy (Fig. 2). A sevenfold increase in hydrogen demand between 2020 and 2050 is estimated to ensure the achievement of net zero emissions in 2050 [10]. With this in view, hydrogen production has to grow, and a many-fold increase in investment will have to be made in the coming years.

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Fig. 2 Key components of a hydrogen economy

The current global hydrogen production from various sources is estimated as 120 MT (in 2022). The International Energy Agency (IEA) has projected an increase in hydrogen demand from 287 MT for a sustainable development scenario to 528 MT for a net zero strategy. It could lead to mitigation of 1.6 to 3.5 MT of GHGs annually up to 2050.

2.1 Hydrogen Sources and Production Pathways Hydrogen, the first element of the Periodic Table, is abundant in the universe but does not exist as a free molecule in the atmosphere. Chemically very reactive, it is present in many chemicals around us, from water and hydrocarbons to polymers and plastics, and many others, including living systems like plants and animals. Hydrogen can be produced from (a) natural and (b) anthropogenic sources by supplying energy in the form of heat, electricity, with or without a catalyst and/ or by using biological and hybrid processes.

2.1.1

Natural Sources

(1) Water Water is foremost among the natural sources. Various methods of production of hydrogen from water are based on thermolysis and electrolysis, by splitting water into hydrogen and oxygen. (i) Thermolysis Thermolysis is a process of thermal dissociation of water by supplying heat. It came to be known as reduction–oxidation (redox) reaction. The Gibbs free energy required is 237.2 kJ/mol, and the temperature required is ~2500 K. Thermolysis reaction, or redox reaction can be written as H2 O heat H2 + 1/2 O2 . −−→

(1)

The source of heat could be a solar concentrating collector using heliostats for achieving high temperatures in the range of ~ 2500 K. Alternatively, nuclear reactor waste heat can be used to produce temperatures in this range. The process is

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completely free from greenhouse gas emissions as solar or nuclear energy is used. Reaching such high temperatures, however, requires enormous energy input and is therefore not practical. A modified approach is thermochemical splitting using metal oxide catalysts as discussed below. (ii) Thermochemical Splitting Using both thermal and chemical cycles, the temperature of dissociation can be brought down. A large number of chemical-driven water-splitting thermochemical cycles have been studied using different metal oxides and chemicals. The overall reaction can be expressed as H2 O heat + chemical H2 + 1/2 O2 . −−−−−−−−−−→

(2)

Both direct and indirect or hybrid methods are used. Using copper chloride, the chemical reaction can be written as Cu2 OCl2 heat 2CuCl2 + 1/2 O2 . −−→

(3)

CuCl2 + H2 O chemical(hydrolysis) 2Cu 2 OCl2 + 2HCl −−−−−−−−−−−−−−→

(4)

2CuCl + 2HCl elctrolysis 2CuCl2 + H2 −−−−−−→

(5)

The direct chemical cycle using sulphuric acid for dissociation of water can be written: H2 SO4 heat H2 O + SO3 −−→

(6)

SO3 heat 1/2 O2 + SO2 −−→

(7)

SO2 + J2 + 2H2 O Hydrolysis 2HI + H2 SO4 −−−−−−→

(8)

2Hl heat H2 + I2 −−→

(9)

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In this process, chemicals used can be recycled and waste production is minimized. Thermochemical water splitting is a research intensive area for improving efficiency and reducing the temperature requirement, for a reduction in cost. (iii) Electrolysis Electrolysis is a process of hydrogen production by passing electric current to split water. It takes approximately 39 kWhr of grid electricity to produce 1 kg of hydrogen. Discovered way back in 1789, electrolysis is highly recommended for the production of green hydrogen by having a source of electricity as solar or wind or other forms of carbon-free energy that may include nuclear and other renewable energy sources. An electrolyser consists of an anode and a cathode separated by an alkaline electrolyte. The chemical reaction can be written as H2 O electricity H2 + 1/2 O2 −−−−−−→

(10)

In this case, electrolyte is an alkaline solution of sodium or potassium hydroxide. Hydrogen and hydroxide are generated at the cathode, and the alkaline electrolyte transports the hydroxide ion (OH) from the cathode to the anode. Hydrogen is produced at the cathode in following reaction. At the anode, 4OH− → O2 + H2 O

(11)

At the cathode, 2H2 O + 2e− → H2 + 2OH−

(12)

The process of electrolysis can take place with a variety of electrolytes. The processes are distinguished from the electrode materials and electrolytes used. The Proton Exchange Membrane (PEM) fuel cell electrolyser technology using solid polymer membranes is well developed. It is more efficient than an alkaline electrolyser but requires deionized water of high purity and is therefore costly. The reactions are At the anode, 2H2 O → O2 + 4H+ + 4e−

(13)

At the cathode, 4H+ + 4e− → 2H2 .

(14)

Solid Oxide Electrolyser Cell (SOEC) technology is under development. Its operation temperature is in the range of 1000 °C, and it is more efficient. Proton Ceramic Electrolyser Cell (PCEC) has ceramic materials as electrolyte and operates at the temperature of 700–800 °C. Anion Exchange Membrane Cell (AEMC), Molten Carbonate Fuel Cell (MCFC), and Intermediate Temperature Steam Electrolyser (ITSE) are other types of electrolysers being researched. The development of an electrolyser to achieve the hydrogen cost of US one dollar for one per kilogram in one decade, is a vital goal for its large-scale use. It would give a major boost to industrial applications in hard-to-decarbonize sectors.

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(iv) Electro-Thermochemical Splitting Electro-thermochemical water splitting is a hybrid process combining electrical and thermal energy with chemical energy. H2 O heat + electricity + chemicals H2 + 1/2 O2 −−−−−−−−−−−−−−−−−−−−→

(15)

Combined use of electricity and heat dissociates water at comparatively lower temperatures. (v) Photo-Electrochemical Splitting This is another hybrid process for water splitting using semiconducting materials, which exhibit electrochemical properties in the presence of light. A semiconductor electrode is used, which when immersed in a water-based electrolyte acts either as a photo-electrode at the cathode or a photo-anode at the anode. By absorption of photons incident on the electrode, either a cathode or an anode creates an electron– hole pair. The current flows causing electrolysis can be enhanced through the use of a photocatalyst. The advantage is that the reaction takes place under ambient conditions and requires no external energy source other than solar. Water dissociation reaction can be written as H2 O photo + electricity + chemical H2 + 1/2 O2 . −−−−−−−−−−−−−−−−−−−−−→

(16)

The process is advancing rapidly. Novel sunlight sensitive nano-structured electrodes increase the operational surface area [11]. The development of new photoelectrochemical materials and photocatalysts is promising research area in view of their high conversion efficiency. (vi) Hydrogen Production from Sea Water Offshore hydrogen production is getting a new thrust for production of hydrogen using sea water electrolysis. Natural sea water is available in large quantities, does not require purification, and is therefore cost-effective. For production of hydrogen using solar energy, solar fuel rigs mounted on a floating platform, act as a floating PV electrolyser for electrolysis of sea water. In one such arrangement, when sheets of titanium mesh coated on one side with a catalyst, say platinum, are suspended in water, separated by a small distance, current flows and H2 and O2 are generated. If the mesh electrode is negatively charged, hydrogen bubbles develop on the side coated with the catalyst. By placing the mesh titled in water, the gas gets detached from the mesh and flows by buoyancy up to a storage chamber. When it is positively charged, oxygen bubbles move to the catalyst-coated side. The oxygen bubbles float into another chamber and get vented out into the atmosphere. In sea water, chlorine evolution also takes place at the anode. Production of hydrogen with 99% purity has been achieved [12]. Sea water can be a potential source of hydrogen. Offshore wind energy can also be used in place of solar energy. A green hydrogen initiative in Germany targeted

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one million tons of green hydrogen production per year by 2035 using a 10 GW of offshore wind park in the North Sea [13]. ‘AquaVentus’ comprises several companies and research institutions to demonstrate green hydrogen production from the offshore wind. It incorporates a large offshore hydrogen pipeline and hydrogen-powered ships to transport it to Germany.

2.1.2

Fossil Fuels

At present nearly 95% hydrogen is produced from fossil fuels, using steam reforming, partial oxidation, or gasification processes as discussed below. (1) Natural Gas Using natural gas or methane, steam reforming is the most developed hydrogen production technology. The chemical reactions are steam reforming or partial oxidation. (vii) Steam Reforming In steam reforming, methane gas reacts with high-temperature steam in the temperature range ~700 °C in the presence of a catalyst under pressure, as below: CH4 + H2 O heat &pressure CO + 3H2 . −−−−−−−−−→

(17)

The hydrogen produced is called grey hydrogen. The carbon monoxide produced is further reacted with water in a water–gas shift reaction using a catalyst, to produce carbon dioxide and more hydrogen: CO + H2 O catalyst CO2 + H2 + (heat). −−−−→

(18)

Hydrogen is separated by using gas separation technique of pressure swing adsorption. Today, nearly 75% of all hydrogen produced is from steam reformation process of natural gas. The process is not so environment friendly. Nearly, 10 kg of CO2 is produced for one kg of H2 . Additional energy is therefore required to capture the CO2 and that makes it blue hydrogen. But it adds to additional consumption of natural gas, which increases by 2.5 times and the cost of hydrogen increased by 1.5 times. In view of limited natural gas resource, search for more efficient processes to produce cost-effective hydrogen with minimized CO2 emissions is underway. (viii) Partial Oxidation Partial oxidation is an exo-thermic process, in which methane is reacted with some amount of oxygen. It is faster than steam reforming but requires an air separation unit for oxygen production. The amount of hydrogen production is somewhat less. Water–gas shift reaction can be used to produce some more hydrogen;

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CH4 + 1/2 O2 → CO + 2H2 (+heat).

(19)

Currently, most hydrogen used in the fuel cell applications is produced from the natural gas using above processes. Other petroleum products such as ethanol and propanol can also be used for hydrogen production. Auto thermal reforming, which is a combination of steam reforming and partial oxidation, has advantages in terms of higher production rate of hydrogen and reduction in cost. (ix) Pyrolysis Pyrolysis is decomposition of organic substances at high temperatures. Coal decomposes at temperature above 500 °C, and natural gas can be decomposed at temperatures above 1200 °C. Biomass undergoes pyrolysis at a pressure of 0.1–0.3 MPa and a temperature varying from 500 to 900 °C. A transition metal catalyst can further reduce the temperature. Cn Hm pyrolysis nC + 1/2 mH2 −−−−−→

(20)

The process has some advantages; it is flexible for any organic hydrocarbon fuel and is free from carbon dioxide generation as oxygen or air is not used. (x) Plasma Arc Decomposition Methane gas, using high voltage at high temperatures, is thermally decomposed into hydrogen and carbon black. The chemical reaction for methane is depicted as CH4 plasmaarc C + 2H2 −−−−−−→

(21)

Methane from gas leakage or landfill emissions can be used to produce hydrogen by this method. Thermal plasma technology provides a higher degree of dissociation. It can be applied for even toxic waste. Higher energy input to create a highvoltage plasma arc, however, inhibits the process from being green. The advantage is the production of carbon black, which can be converted to ‘graphene’. (2) Coal (xi) Coal gasification Coal gasification, as opposed to combustion converts to hydrogen directly. The reaction takes place at high temperatures in the presence of oxygen and steam. Products of coal gasification are carbon monoxide, carbon dioxide, and hydrogen in a reaction depicted as below. Cn Hm (Coal) + O2 + H2 O heat &pressure CO + CO2 + H2 + wastespecies. (22) −−−−−−−−−→ The carbon monoxide is further converted to carbon dioxide and some more hydrogen in a water–gas shift reaction. The hydrogen produced is called brown

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hydrogen. To make the process climate friendly, the carbon dioxide produced in the process must be sequestered. Carbon sequestration is the process of capturing CO2 from its large point sources and utilizing it into value-added products or storing it away from the atmosphere. Using Koppers–Totzek coal gasification process, pure hydrogen up to 97% purity has been produced from coal with carbon sequestration applied [14]. For a coal-dominant country, the application of carbon sequestration, or CCUS with coal gasification has the potential to increase hydrogen use in hard-to-decarbonize sectors of economy like steel and chemicals industries. National Aluminium Company (NALCO), National Thermal Power Corporation (NTPC), Tata Steel, and Chemicals & Fertilizers are some of the industries that have successfully demonstrated the CCUS technology in India.

2.1.3

Anthropogenic Sources

Human activities are giving rise to increasing gaseous, liquid, and solid waste pollution. Hydrogen can be produced from all of these. The various production pathways for solid or liquid waste are as follows: (1) Biomass (xii) Gasification Biomass or solid waste is an abundant, cost-free resource. The use of biomass in place of coal in gasification reduces carbon dioxide emissions. The chemical reaction for biomass gasification or conversion is somewhat similar to coal gasification. No extra oxygen is supplied in this case, and the reaction can be written as Cx Hy Oz + H2 O heat & pressure CO + CO2 + H2 + otherspecies. −−−−−−−−−−→

(23)

Biomass conversion is a complex reaction; it does not gasify easily and requires a catalyst for the reaction to proceed smoothly. The advantage is it uses waste, a renewable resource that makes it favourable for hydrogen production, that can be termed as green. Similar to coal, the water–gas shift reaction can be utilized to produce more hydrogen. For the separation and purification of hydrogen, pressure swing adsorption or other low-cost membrane technology can be used. With the growing concern for increasing plastic waste, studies have been made for the conversion of the plastic waste into gases like methane and hydrogen. Plastic can be converted to hydrogen by pyrolysis or gasification. As plastics are heavy polymeric systems, different metal catalysts are being investigated to make it feasible. (xiii) Dark Fermentation and Photo-Fermentation For the conversion of liquid biomass using anaerobic bacteria, dark fermentation can lead to hydrogen, carbon dioxide, and acid derivatives. The reaction can be written as

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Cx Hy Oz anaerobic bacteria H2 + CO2 + acid derivatives. −−−−−−−−−−−→

(24)

The biological processes operate at room temperature, and therefore, they are low energy consuming and have low efficiency. In photo-fermentation, the organic matter in the presence of aerobic bacteria or water sensitive micro-organisms gets converted to hydrogen [15]. The reaction is depicted as Cx Hy Oz + H2 O micro organism xCO2 + 1/2 H2 . −−−−−−−−−−→

(25)

This process takes place at ambient temperatures and pressure, but has a low rate of hydrogen production. (xiv) Biophotolysis Using Micro-algae Biophotolysis is a process of water decomposition using micro-algae or cyanobacteria in an anaerobic environment in the presence of light H2 O light + microalgae H2 + 1/2 O2 −−−−−−−−−−−−→

(26)

The process, similar to other biological methods, takes place at room temperature using water and algae and produces no waste. It has potential for sustainable production of green hydrogen, provided the process efficiency can be enhanced. (xv) Wastewater Wastewater from different anthropogenic activities, produced in large quantities can be potential resource for hydrogen. It has a high organic waste content. Conversion of wastewater in the presence of a photocatalyst by degradation of organic pollutants can occur through dark fermentation and photo-fermentation. Novel approaches for hydrogen production by using wastewater have been demonstrated or are under development. The application areas are: municipalities sewage water, distilleries, textile industry wastewater [15, 16], and wastewater from oil and gas assets. Using nano-porous electrodes made from Cu/CuO nanoparticles prepared by heating copper foil for 1 h at 540 °C, 14.6% of hydrogen production from the sewage water was reported [17]. A wastewater plasmalyzer using Graforce Membrane Technology has been demonstrated to separate hydrogen from methane and wastewater with solar or wind as energy resources [18]. Hydrogen gets its colour from the source of its generation. Various colours of hydrogen and the materials and energy resources used are shown in Fig. 3. Celik and Yildiz [19] noted that the application of green chemistry principles suggests; that not all hydrogen production pathways are ‘green chemistry’ friendly. The production technologies can be grouped into four categories: electrical, thermal, hybrid and biological, determined by the form of energy input. Analysing the application of twelve green chemistry principles to the identified fifteen hydrogen production technologies, it was indicated that only four of them, namely electrolysis, biomass

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Fig. 3 Colours of hydrogen and process of production

Table 2 Hydrogen production technologies, their conversion efficiency, and maturity level S. no

Technology

Feedstock

Efficiency

State of maturity

1

Steam reforming

Hydrocarbons

70–85%

Commercial

2

Partial oxidation

Hydrocarbons

60–75%

Commercial

3

Autothermal reforming

Hydrocarbons

60–75%

Near term

4

Plasma reforming

Hydrocarbons

9–85%

Long term

5

Biomass gasification

Biomass

35–50%

Commercial

6

Aqueous phase reforming Carbohydrates

35–55%

Medium term

7

Electrolysis

H2 O + electricity

50–70%

Commercial

8

Photolysis

H2 O + sunlight

0.5%*

Long term

9

Thermochemical water splitting

H2 O + heat

NA

Long term

Source Kalamaras M. Christos. and Efstathiou M. Angelos, 2013, [20]

gasification, photo-electrochemical, and biological processes, are environmentally friendly and make hydrogen production green. Hydrogen production technologies from different chemicals present on the earth are under development. Only some are reaching the commercial stage. Table 2 provides a summary of various technology options, feedstock used, efficiency of the process, and maturity [20]. The efficiencies ranging from 30 to 85% have been achieved, with some exceptions.

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2.1.4

M. Goel

Other Production Pathways

Floating Artificial Leaf Concept Artificial photosynthesis is a photo-electrochemical process that mimics natural photosynthesis, where plants capture carbon dioxide from the air and, in the presence of the sun, water and chlorophyll, produce carbohydrates. The energy gets stored in plants and adds to their growth. In artificial photosynthesis, a photosensitive pigment is used, which acts as a catalyst to capture CO2 from air to achieve an enhanced reaction with sunlight for the splitting of water and generating hydrogen, also known as solar hydrogen. The use of multi-junction solar cells and photocatalysts in the photo-electrochemical process performs better. Floating artificial leaf is an emerging concept for producing green hydrogen. A large number of materials have been tested. Extensive research has been carried out in this area in recent years. Hydrogen Production Using Ammonia Ammonia decomposition with and without catalysts has been researched to produce hydrogen at 28.3% efficiency. El-Shafie et al. [14] studied ammonia decomposition using plasma technology to produce 5N ~ 99.999% purity hydrogen with higher efficiency. Natural Hydrogen from Inside the Earth The possibility that hydrogen may be trapped inside the earth is not completely ruled out. In 1888, D. Mandeleev of Periodic Table fame, reported that hydrogen is seeping from cracks in a coal mine in Ukraine [21]. Over 1,000 such seepages have been reported from time to time. According to USGS earth may hold 1 trillion tons of hydrogen. First bore well was dug in USA by a start-up in 2019. Finding reserves of hydrogen can be a solution for the shortage of gas as a fallout of the on-going war between Russia and Ukraine. The shallow iron-rich rocks carrying olivine across the globe trap hydrogen and may allow earthly hydrogen to be collected. Natural hydrogen is called white hydrogen. Potential deposits of white hydrogen have been reported in France in the Lorrain region.

3 Hydrogen Storage and Transport Hydrogen from the place of production needs to be packaged by compression and cooling before being transferred to the location of use. It is compressed to a pressure of 0.6 to 70 MPa and cooled to temperatures of 15 °C to −250 °C to help reduce the storage space requirement. In storage and transport, safety considerations are foremost. Hydrogen is a less hazardous energy carrier regarding fire safety and temperature changes than gasoline, but more unsafe with pressure changes. Hydrogen is a low-density gas; while, one kg of hydrogen holds about four times the energy of gasoline of the same weight, the space it occupies is much larger. Liquid hydrogen

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requires cooling to −253 °C and is less dense than gasoline. The options for transport to the place of use are tankers, pipelines, and materials bonding. Tankers Tankers are preferred for long-distance transport of compressed and cooled hydrogen via trucks, ships, or railways. A payload of up to 4 tonnes of liquid hydrogen with a capacity of about 50 m3 can be carried through shipment [22]. A compressed hydrogen tank has a lower capacity ~ 20–25m3 . In liquefied form at −253 °C on board, storage for hydrogen for fuel cell vehicles is an energy-intensive option, that occupies more space, and the loss of hydrogen at the ambient temperature can be high. The energy-per-unit weight of a gasoline tank is higher. Salt caverns have been used to store compressed and cooled hydrogen in quantities up to 1000 m3 . Pipelines Pipelines are suitable for transporting large hydrogen volumes, even though they are expensive. Pumps need to be installed to energize the compressor and maintain gas flow into pipelines. There has been a proposal to use existing natural gas pipelines for transport by blending hydrogen with gas. 100% hydrogen can cause embrittlement in materials like plastic and can leak through with time. Composites are found to be better. Care needs to be taken for an appropriate selection of materials for the pipelines. Hydrogen pipeline infrastructure at present is approximately 5000 km. Through Material Bonding Different materials can store hydrogen by physical or chemical adsorption. The physical bonding is by van der Waals forces in metal organic frameworks and chemical bonding is in metal hydrides. With physical bonding, hydrogen generation at the destination is proving more cost-effective. Material-based chemical storage in metal hydrides can be a solution, but R&D is needed to compete with the physical storage methods. Extensive research is being carried out.

4 End-Use Technologies The hydrogen economy is about sustainable large-scale industrial applications of hydrogen to replace the fossil fuel economy. The five leading hydrogen end-use technologies in various sectors of the economy are discussed below: Fuel Cells Fuel cells are the optimal H2 conversion environment friendly technology for electricity generation. It can be adapted for different hydrogen end uses. The fuel cells operate at various loads and under ambient conditions. Different fuel cell technologies are proven for low-temperature residential requirements, automobiles, and other commercial and industrial applications. In the transport sector, economics and performance of hydrogen fuel cell vehicles to compete with gasoline and storage

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battery electric vehicles (EVs) need to be established. Several types of fuel cells exist, developed, commercialized, and are under development. In Gas Turbines Hydrogen has been used in commercial natural gas turbines for power generation, wholly, or in hydrogen-rich blends. Efficient and cost-competitive micro and smallscale gas turbines are under development. 100% hydrogen-fueled gas turbines are expected to become feasible by 2030. Thermal NOx formations during combustion and high heat transfer coefficients, are the two main challenges that need to be addressed. Internal Combustion Engines Internal combustion engines (ICEs) being efficient and cost-competitive gas engines for automobiles, H2 -fuelled ICEs, have long been investigated. ICEs have been used for electricity generation, heat generation and maritime transport. However, for hydrogen a bigger tank on board is an issue because of its low density compared to gasoline. As Chemical Reactors Hydrogen acts as a chemical building block for conversion processes like Haber– Bosch ammonia and methanol synthesis. Several chemical reactor configurations are available for the conversion of hydrogen through CO2 hydrogenation applications for producing value-added materials. These H2 –CO2 chemical conversion reactors are becoming increasingly important in CCUS, where CO2 is activated and converted into C-based fuels or chemicals [23]. A Fusion Reactor A fusion reactor uses heavy hydrogen isotopes: deuterium, and tritium to reach the Lawson criterion requirements for fusion. The approach is to heat these molecules to a high temperature of around 100 million degrees so that the colliding atoms have sufficient energy to undergo nuclear fusion and produce enormous amount of clean energy. This technology is proven, and has a high potential for achieving the targets of net zero, yet, to become operational. A multi-country collaborative International Thermonuclear Experimental Reactor (ITER) is being built in France with a 500 MW capacity and is expected to become active in 2025.

5 Policy Landscape in India To forecast hydrogen production at a place, Gul et al. [24], using MARKAL analysis, established that hydrogen application growth in different sectors needed strict constraint policies. Therefore, hydrogen policy development has a significant role in the achievement of the hydrogen economy. Starting with a vibrant climate policy, India, with the aim of attaining the Paris Agreement targets, has taken several climate

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policy actions. The National Action Plan on Climate Change (NAPCC) was adopted on June 30, 2008; the focus has been on climate mitigation and adaptation in different sectors of the economy. Several national missions have been launched, namely National Solar Mission National, Mission for Enhanced Energy Efficiency, Green India Mission, National Electric Mobility Mission, National Smart Grid Mission, and National Mission on Transformative Mobility & Battery Storage. India submitted its Intended Nationally Determined Commitments (INDCs) to the UNFCCC on 2 October 2015, reflecting India’s commitment to ecologically sustainable economic development. Subsequently, at the 26th UN Conference of Parties (COP26) held in Glasgow in 2021, India updated the NDCs goals to reach net zero emissions by 2070. National Hydrogen Energy Board 2004 In a move towards a hydrogen economy, hydrogen production and fuel cell research had attracted the greatest attention of the government and corporate sector, commencing in 2004 when the National Hydrogen Energy Board was constituted under the Ministry of New and Renewable Energy. The National Hydrogen Energy Roadmap 2006 identified technology gaps and challenges to be overcome for a largescale introduction of hydrogen as an energy carrier in a phased manner and suggested suitable pathways. The two significant initiatives were (i) Green Initiative for Future Transport (GIFT) aiming to develop and demonstrate hydrogen-powered IC engines and fuel cell-based vehicles and (ii) Green Initiative for Power Generation (GIP), for developing and establishing hydrogen-powered turbines and fuel cell-based decentralized power generating systems. India is an active participant in the ‘International Partnership for the Hydrogen and Fuel Cells in the Economy (IPHE)’ programme launched way back in 2003 for coordination among hydrogen initiatives and organizations from various countries, leading to global hydrogen and fuel cell collaborations [25]. However, by 2020, the roadmap core targets of the—number of automobiles on roads [26] and the development of coal gasification power plants—could not be fulfilled due to technology and investment crunch. Mission Innovation India, as a core coalition member of Mission Innovation, a programme launched in 2015, participated in the Hydrogen Mission of the clean energy programme. The proposed ‘Hydrogen Valley’ covered the entire hydrogen value chain (production, storage, distribution, and final use) for several hydrogen applications supported by the Department of Biotechnology and the Department of Science and Technology under the aegis of Ministry of Science and Technology. Government of India supported basic research on hydrogen production from autotrophic and heterotrophic micro-organisms, the development of materials for hydrogen storage, and fuel cells by accelerating investment in clean energy development, aiming to meet Paris Agreement 2015 targets. International Platform on Hydrogen Economy, an industryacademia conclave as part of the Hydrogen Valley, paved the way for India to form partnerships with international research institutes and to explore green hydrogen production opportunities. Through these early initiatives, many Indian institutions, including the Indian Space Research Organization (ISRO), Indian Oil Corporation

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(IOCL), Bharat Heavy Electricals Limited (BHEL), Indian Institute of Science (IISc), Bangalore, CSIR Laboratories, Indian Institute of Technologies (IITs), and several universities, got a boost to actively engage in research on hydrogen and fuel cell technologies. Panchamrit Action Plan In COP26, India proposed a fivefold strategy to limit the rise in global temperature to 1.5 °C with a Panchamrit action plan aimed at. • • • • •

Increasing India’s non-fossil energy capacity to 500 GW by 2030 Meeting 50% of its energy requirements from renewable energy until 2030 Reducing India’s projected carbon emissions by one billion tonnes by 2030 Reducing the carbon intensity of the economy by 45% by 2030 Achieving the target of net zero by 2070.

In response to this, India has updated its Nationally Determined Contribution (NDC) goals to reflect the Panchmrit action plan, i.e. to reduce emissions by 45%, generate 50% of power from renewable energy sources, and develop a roadmap to reach net zero emissions by 2070. The Prime Minister of India, Mr. Narendra Modi, announced the launch of a national hydrogen mission on 15 August 2021. India declared its first green hydrogen policy in February 2022, aiming to realize the potential for hydrogen energy to play a significant role in the nation’s long-term energy future. The policy enables power exchange, the development of renewable energy capacity, and hydrogen storage capabilities, aimimg at other facilitating mechanisms for industry to grow. An ambitious goal of making India a global hub and achieving green hydrogen production of 5 MTPA by 2030 is set. National Green Hydrogen Mission The National Green Hydrogen Mission (NGHM) launched on 4 January 2023, with a budget of INR 19,744 million aims to provide a comprehensive action plan for establishing a green hydrogen ecosystem in the country [27]. An implementation plan for catalyzing a systemic response to the opportunities and challenges guidelines and creating opportunities for investments across the green hydrogen value chain has evolved. One of its sub-components the ‘Strategic Interventions for Green Hydrogen Transition (SIGHT)’ programme [28] targets domestic manufacturing of electrolysers and production of green hydrogen. The Mission is to give focus on the following application areas, among others. • E-mobility—fuel cell-based Electric Vehicles • Industrial applications—steel, chemicals and other heavy industries • Energy storage applications. India’s hydrogen policy development highlights are summarized in Table 3.

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Table 3 India’s Hydrogen Policy Development 2004 India set up the National Hydrogen Energy Board to examine its production from various sources. 2006 The Ministry of New and Renewable Energy laid out the National Hydrogen Energy Road Map identifying the Green Initiative for Future Transport (GIFT) and the Green Initiative for Power (GIP) generation as two major green energy initiatives. 2006 A R&D programme on ‘hydrogen energy and fuel’ was launched to address challenges in the production of hydrogen focusing on improving the efficiency of water-splitting reaction and finding newer materials, catalysts, and electrodes. A number of institutions got engaged in fuel cell technology research. 2015 India participated in the ‘Mission Innovation Challenge for Clean Hydrogen’, USA, and shared the objective of accelerating the development of a global hydrogen market by identifying and overcoming key technological barriers to the production, distribution, storage, and use of hydrogen at the GW scale. 2018 The Department of Science and Technology, Government of India, intensified R&D support under the Clean Hydrogen Mission and is in the process of setting up at least three hydrogen valleys by 2030. 2021 On 15 August 2021, the Government of India announced the launch of National Hydrogen Mission (NHM) while commemorating the 75th anniversary of Azadi ka Amrit Mahotsava to celebrate India’s energy freedom. 2022 Ministry of Power, Government of India, announced ‘Green Hydrogen Policy’ with the aim to meet India’s climate action targets and making India a green hydrogen hub, and to achieve green hydrogen annual production of 5 MMT by 2030. 2022 The Ministry of Petroleum and Natural Gas, Government of India, created a ‘Hydrogen Corpus Fund’ (HCF) for funding Research and Development (R&D) to support pilot projects on green hydrogen and strengthen infrastructure. The pilot project on the grey Hydrogen and Hydrogen CNG (H-CNG) initiative, where hydrogen is blended up to 18% in CNG, has become operational. 2023 ‘National Green hydrogen Mission’ launched on 4 January 2023 with a budget allocation of INR 19,744 million crores. The Ministry of New and Renewable Energy (MNRE) has drawn up a specific implementation plan.

6 Perspectives for a Hydrogen Economy in India Making significant impact on carbon dioxide emissions and replacing 10% of worldwide fossil fuel-based electricity, would require 1 billion ton per year of hydrogen production. For total replacement of fossil fuels, 10 billion tons of hydrogen production per annum is estimated [29]. Mitrova et al. [22], from a study for hydrogen economy as a path towards low-carbon development, identified three main pillars for the sustainable development of the global hydrogen market as (i) technology development, (ii) sustainable market support, and (iii) attracting international investment. A smooth transition towards hydrogen, would therefore require a shift in the approach in R&D for hydrogen production technologies, the creation of minimum physical infrastructure for transport, the development of a sustainable hydrogen supply chain, and the cost-effectiveness of these for acceptance by all the stakeholders. The policy think tank of the Government of India, NITI Aayog viewed Indian perspectives

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on the hydrogen economy in India in terms of reduced emissions, reduced dependence on imported fuel, and therefore a reduced financial and ecological burden [30]. Harnessing green hydrogen can substantially spur industrial decarbonization and economic growth in the coming decades. ‘The next steps at the policy level could involve arriving at the correct mix between mandates/regulations and price instruments’, said Suman Bery, Vice Chairman, NITI Aayog. Electrolyser Development and Manufacturing In India, rapid growth has taken place in RE capacity addition from 39.5 GW in 2014 to 151 GW in 2021 with a fall in solar tariff by 70% and wind tariff by 50% during this period. From the analysis conducted by CEEW for a hydrogen roadmap study in the short term, medium term, and long term, it was concluded that scaling up global annual manufacturing capacities to bring down the equipment cost of electrolysers can only lead to the low production cost of green hydrogen in the long run [31]. With adequate financial mechanisms such as production-linked incentive (PLI) schemes, 25 GW of the manufacturing capacity of electrolysers may be achieved by 2028, which would mean an abatement of nearly 50 MMT of annual greenhouse gas emissions. The Mission roadmap targets development of green hydrogen production capacity of at least 5 Million Metric Tonne (MMT) per annum with an associated renewable energy capacity addition of about 125 GW and 60–100 GW electrolyser capacity by 2030 [28]. It is vital to ensure that the integrated technology development of electrolysers, hydrogen storage, transport, and end use, along with the policy support, identification of strategic research priorities, and investment receives timely attention. Scaling up Hydrogen Economy by Capturing Carbon Dioxide Bossel et al. [9] analysis has revealed that much more energy is needed to operate a hydrogen economy than is consumed in today’s energy economy unless we consider not only the closed hydrogen (water) cycle but also the closed carbon (CO2 ) cycle. In a natural gas reforming producing grey hydrogen, the carbon dioxide present in the gas can be separated and removed by chemical solvents or physical separation methods beforehand. The energy requirement is relatively small and can typically be recovered from the hydrogen production process [32]. In a natural gas hydrogen plant with CCS, carbon emissions in the exhaust stream need to be captured and transported for utilization or to a permanent underground storage location. It consumes significant energy and would add to the cost. In India, taking into account all associated factors, the estimated cost of grey hydrogen is computed as INR 150–200/ kg, and for green hydrogen, it is INR 350/kg [33]. Although the cost of producing hydrogen from natural gas is lower than from electrolysis of water, with more than 55% of gas demand met through imports, it may not be feasible to import the gas and produce hydrogen that is not contributing to decarbonization. On the other hand, India having rich coal reserves, has set a target for 100 million tonnes of coal gasification by 2030. Coal gasification with CCUS would provide an opportunity to produce blue hydrogen in the long run. A pilot project between Japan and Australia named Hydrogen Energy Supply Chain (HESC) has successfully

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demonstrated carbon dioxide capture while generating hydrogen using coal gasification from the Latrobe Valley in Australia to produce 99.999% pure (blue) hydrogen. ‘Suiso Frontier’, the ocean-going liquid hydrogen carrier ship, has been designed to transport it at −253 °C. The project’s aim is to commercialize the technology to produce 225,000 tonnes of liquid hydrogen per year from coal with CCS. It would reduce global CO2 emissions by 1.8 million tonnes annually, equivalent to emissions from 350,000 gasoline-driven cars [34]. Getting Carbon Price as Stimulus to Industry Carbon has been recognized as a global tradeable good way back in the Kyoto Protocol, signed in 1997 and ratified in 2002. It led to international trade in carbon credits through a mechanism called the Clean Development Mechanism (CDM). It was reaffirmed in the Paris Agreement of 2015, and under Article 6, a country is able to transfer carbon credits gained through the reduction of greenhouse gas (GHG) emissions in order to assist other countries in meeting their climate targets. In India, schemes like Renewable Purchase Obligations (RPOs) and energy-savings certificates under the Perform, Achieve and Trade (PAT) exist. With the rising hydrogen demand in industry, a carbon credit trading scheme by amending the Energy Conservation Act 2001 aims to establish carbon markets. The Energy Conservation (Amendment) Bill 2022 (passed in Parliament in December 2022) forestalls that meeting decarbonization targets by creating sustainable demand for hydrogen in energyintensive sectors would help generate carbon markets. In the first phase between 2023 and 2025, it is proposed to convert PAT certificates to carbon credits, with anticipated green hydrogen demand growing more than fourfold by 2050, representing almost 10% of global hydrogen consumption. The initial hydrogen demand growth is expected from the refinery, ammonia, and chemical industries, while steel industry and heavy-duty vehicles would create demand in the long run. In this manner, adoption of green hydrogen could result up to 3.6 giga tonnes of cumulative CO2 emission reductions between 2020 and 2050 [30]. There will be savings in energy imports of $300 billion by 2050. Intensification of R&D Many institutions, including the Indian Institute of Science (IISc), Bangalore, CSIR laboratories, Indian Institute of Technologies (IITs), and universities, are actively engaged in research on hydrogen and fuel cell technologies. In addition, corporate organizations in the public and private sectors, viz. National Thermal Power Corporation (NTPC), Oil & Natural Gas Corporation (ONGC), Bharat Heavy Electricals Limited (BHEL), Refineries, Reliance Industries Ltd, (RIL), Larson and Toubro (L&T), Adani Group, Jindal Power, ReNew Power, Tata Steel, Tata Motors, and many others, are currently making intense efforts to produce green hydrogen at a lower cost. Indian Oil Corporation R&D centre was the first to establish a hydrogen dispensing station and a facility for hydrogen vehicle testing in the country. Some of the recent initiatives for the production of green hydrogen include.

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• Signing of a MoU between Indian Institute of Science (IISc), Bangalore, and the Research and Development Centre of Indian Oil Corporation Limited (IOCL) for biomass gasification-based hydrogen generation and producing it at an affordable price • Commissioning of a green hydrogen manufacturing plant in the Hazira Complex with an electrolyser capacity of 800 kW • Reliance Industries Ltd (RIL) plans to develop and manufacture hydrogen electrolysers and has announced a target to reach the production of green hydrogen at $1 per kg in one decade (1-1-1) • Indian Oil Corporation Limited (IOCL) plans to set up a hydrogen manufacturing facility at Mathura Refinery and operate 15 fuel cell buses in NCR along with Tata Motors • Bharat Petroleum Corporation Limited (BPCL) proposes a 20 MW electrolyser at its Bina Refinery, Madhya Pradesh • Hindustan Petroleum Corporation Limited (HPCL) is setting up a 370 MT green hydrogen plant at its Vizag refinery • Gas Authority India Ltd. (GAIL) will build one of India’s largest Proton Exchange Membrane Electrolyser at Guna, Madhya Pradesh, to produce green hydrogen • National Thermal Power Corporation (NTPC) plans to set up a manufacturing facility for green hydrogen production in Leh Ladakh and Runn of Kutch in Khovada, Gujarat • Larsen & Toubro (L&T) plans to set up a gigawatt-scale manufacturing facility for electrolysers based on France’s electrolyser manufacturer, McPhy Energy technology in India. Indian companies are joining the World Hydrogen Council, having a long-term vision to develop the hydrogen economy. A green hydrogen-based economy faces many challenges across the hydrogen value chain. The economic and technical challenges to create sustainable demand for green hydrogen in various sectors of the economy can be stated below. • Lack of applied research in various sectors of the economy • Limitations in the location of a hydrogen plant in the vicinity of a RE source • High energy consumption in generation, conversion, and transportation of hydrogen. • Large-scale manufacturing of low-cost electrolysers to produce green hydrogen • Development needs for hydrogen storage facilities • Lack of infrastructure for hydrogen filling stations • Lack of specialized skilled work force for a transition to hydrogen in place of fossil fuel • Adoption of carbon capture and storage for blue hydrogen generation using fossil fuels • CO2 sequestration adding to the energy penalty • Lifecycle analysis of impacts on climate change from the use of blue hydrogen in place of green hydrogen.

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7 Conclusions After a long dominance of fossil fuels for over seventy years, the energy sector is transitioning to clean energy sources such as renewables, nuclear, and other carbonfree sources, viz. hydrogen. Hydrogen is carbon-free, and it can be harnessed to meet energy demands. It has a higher energy content per kg of fuel and is safer than many other fuels. A brief history of hydrogen suggests that there have been moves from time to time for a hydrogen economy on different premises, which include resource constraints, environmental sustainability, and climate change. Hydrogen is a versatile energy carrier towards the decarbonization of economies if it is produced at an affordable cost. It does not contribute to GHG emissions, and stores excess energy from RE and other sources. Nonetheless, climate action to achieve net zero from the hydrogen economy raises vital questions; how can green hydrogen be produced costeffectively in a sustainable supply chain; what is the best source of hydrogen; how green hydrogen production targets be met; would blue hydrogen compete with green hydrogen; how can energy use across the value chain be minimized? Hydrogen can be produced from a wide variety of sources. Both natural and anthropogenic sources can generate hydrogen through the application of technology. Production of hydrogen from natural gas reforming is the most mature technology today, with a 75% share of total global production, but it is not a solution for decarbonization. Carbon footprints from natural gas conversion are about ten kg per kg of hydrogen. Therefore, capturing carbon dioxide is imperative to make it environmentally benign. Using coal gasification with carbon capture and storage, both pre- and post-combustion CO2 capture systems may become feasible in the next decade to serve various end-use applications. Biomass gasification and pyrolysis are proving to be possible solutions for green hydrogen production. Wastewater around the world can also have potential for green hydrogen generation. India has set an ambitious goal of creating a global hub for green hydrogen and has announced a National Green Hydrogen Mission. Electrolyser development using electricity from RE for water splitting is targeted. As the cost of solar and wind technologies is falling due to economies of scale, increasing renewable energy share can be the potential source of hydrogen supplying power 24 × 7. To make a green hydrogen economy a reality, sources other than water would be crucial. The research has evidenced that besides electrolysis of water and biomass gasification, hybrid and biological processes are environmentally friendly and make hydrogen production green. There are many benefits to using waste biomass in terms of an opportunity to save water because of water scarcity, decarbonization of the transport sector, and a solution for achieving ‘circular economy’. The debatable issue therefore arises; whether to have ‘Waste to energy’ or ‘Waste to hydrogen’ in the national policy framework. By 2050, the future global vision offers that hydrogen energy and fuel cell power will be abundant, reliable, and affordable in all sectors of the economy. For a largescale transition to hydrogen, not only technologies for production but also the development of storage facilities and delivery networks have a vital role. As of now, the

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cost of transitioning to a hydrogen economy is way ahead. India is making strides towards a hydrogen economy by taking initiatives like the National Green Hydrogen Mission and the SIGHT programme. Many institutions have conducted immense research on hydrogen and fuel cells in India, which has not been adequately publicized. Green hydrogen offers an opportunity to make India energy independent by making identifiable choices and increasingly investing in Research and Development (R&D), especially in search for new materials for cost-effective catalysis and fuel cell technology, to develop amenable processes. In addition, innovations are required to make the technologies user friendly.

References 1. https://www.ipcc.ch/report/ar6/wg1/ 2. Gauri J (2022) Mega trends in energy transitions. http://ccri.in/pdf/ACBHPE-2022/ACBHPE2022-Proceeding.pdf 3. https://en.wikipedia.org/wiki/The_Mysterious_Island 4. https://www.airships.net/hindenburg/disaster/ 5. Gregory DP (1973) Sci Am 228(1):13–21 6. The Hydrogen Economy: Opportunities, Costs, Barriers, and R&D Needs, National Academies Press (2004). Available at https://nap.nationalacademies.org/catalog/10922/the-hydrogen-eco nomy-opportunities-costs-barriers-and-rd-needs 7. https://www.csis.org/analysis/japans-hydrogen-industrial-strategy 8. https://hydrogencouncil.com/en/about-the-council/ 9. Bossel U, Eliasson B (2003). Energy and the hydrogen economy. https://afdc.energy.gov/files/ pdfs/hyd_economy_bossel_eliasson.pdf 10. https://www.iea.org/reports/the-future-of-hydrogen 11. Li X, Hao X, Abudula A, Guan G (2016) Nanostructured catalysts for electrochemical water splitting: current state and prospects. J Mater Chem A 4:11973–12000. https://doi.org/10.1039/ C6TA02334G 12. https://spectrum.ieee.org/floating-solar-fuel-rigs-could-produce-hydrogen-fuel 13. https://www.rwe.com/en/research-and-development/hydrogen-projects/aquaventus/ 14. El-Shafie M, Kambara S, Hayakawa Y (2019) Hydrogen production technologies overview. J Power Energy Eng 7:107–154. https://doi.org/10.4236/jpee.2019.71007 15. Rashwan Sherif S, Ibrahim D, Atef M (2021) A journey of wastewater to clean hydrogen: a perspective. Int J Energy Res 45:6475–6482.https://doi.org/10.1002/er.6279 16. https://www.futurebridge.com/industry/perspectives-energy/green-hydrogen-from-wastew ater-a-viable-option/ 17. https://statnano.com/world-news/91101/Hydrogen-Fuel-Generation-from-Sewage-WaterUsing-Nanoporous-Electrode 18. https://www.medicaldevice-network.com/research-reports/graforce-develops-plasma-electr olysis-technology-for-green-hydrogen-production/ 19. Dicle C, Meltem Y (2017) Investigation of hydrogen production methods in accordance with green chemistry principles. Int J Hydrogen Energy 42(2017):23395–23401. https://doi.org/10. 1016/j.ijhydene.2017.03.104 20. Christos KM, Angelos EM (2013) Hydrogen production technologies: current state and future developments. Hindawi Publishing Corporation, Conference Papers in Energy, Volume 2013 Article ID 690627. https://doi.org/10.1155/2013/690627 21. Zgonnik V (2020) The occurrence and geoscience of natural hydrogen: a comprehensive review. Earth Sci Rev 203:103140

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22. Tatiana M, Yury M, Dmitry C (2019) The Hydrogen Economy- a path towards low carbon development, SKOLKOVO, Moscow School of Management, E:/C%20Drive%20Data/Downloads/ SKOLKOVO_EneC_Hydrogen-economy_Eng%20(1).pdf 23. Samrand S, Najari S, Hessel V, Wilsond K, Keil FJ, Concepción P, Suib SL, Rodrigues AE, Recent advances in CO2 hydrogenation to value-added products—Current challenges and future directions. https://www.osti.gov/pages/servlets/purl/1776508 24. Gul T, Kypreos S, Turton HL et al (2009) An energy-economic scenario analysis of alternative fuels for personal transport using the Global Multi-regional MARKAL model (GMM). Energy 34:1423–1437 25. https://www.iphe.net/ 26. National Hydrogen Energy Roadmap (2006). http://164.100.94.214/sites/default/files/uploads/ abridged-nherm.pdf 27. https://mnre.gov.in/img/documents/uploads/file_f-1673581748609.pdf 28. https://pib.gov.in/PressReleasePage.aspx?PRID=1888547 29. Arutyunov V (2021) On the sources of hydrogen for the global replacement of hydrocarbons. Academia Lett, Article 3692. https://doi.org/10.20935/AL3692. 30. Harnessing Green hydrogen: Opportunities for Deep Decarbonisation in India, Niti Aayog, June 2022. E:/C%20Drive%20Data/Downloads/Harnessing_Green_Hydrogen_V21_ DIGITAL_29062022%20(3).pdf 31. Biswas T, Yadav D, Baskar AG (2020) A green hydrogen economy for india: policy and technology imperatives to lower production cost, CEEW & Shakti Foundation 32. Bauer C et al (2022) On the climate impacts of blue hydrogen production Sustainable Energy Fuels, 6, 66–75, open access, https://doi.org/10.1039/D1SE01508G 33. Ujwal S, Santosh J (2021) Green hydrogen economy and opportunities for India. IOP conference series: materials science and engineering,1206 , 012005. https://doi.org/10.1088/1757899X/1206/1/012005 34. https://research.csiro.au/hyresource/hydrogen-energy-supply-chain-pilot-project/

Green Hydrogen: Potential Master Key for Combating Climate Change Shweta Gupta, Ankit Gupta, Hemant Bherwani, and Rakesh Kumar

Abstract India has committed to reduce the emissions intensity of its GDP by 45% by 2030, as compared to 2005 levels, under the Paris Agreement on climate change. A shift in energy production and use can be a key starting point to drive these commitments. Green hydrogen (GH)-driven energy is emerging as a viable alternative to fossil fuels and battery-powered mobility systems. Strong hydrogen demand growth and the adoption of cleaner technologies for its production enable green hydrogenbased fuels to avoid up to 3.6 Gt CO2 emissions between now and 2050 to contribute towards net-zero vision and climate risks. Developed economies like the European Union, Australia, and Japan have already drawn a hydrogen roadmap to achieve green economic growth. Developing countries like India can also decarbonize their energyintensive sectors such as industry, transport, and power by moving towards hydrogen economy. India has announced National Green hydrogen Mission and is adopting GH-based economy by working on R&D, especially with respect to technology development and advancement, finding import substitutes, formulating guidelines and policies on environment, health and safety. Stakeholders’ engagement is also vital for harnessing the power of this green fuel to reduce the impacts of climate change and promote Aatma Nirbhar Bharat. The chapter outlines the potential benefits of using GH as a vital part of the total energy basket and further developing a national road map for hydrogen that supports a stronger and faster energy transition beyond India’s current climate change initiatives. Towards the end, a possible way forward has been suggested for harnessing the power of GH that can help capitalize on value creation. Learning objectives: • Clean energy-based economy of India • Need for moving towards hydrogen economy S. Gupta · A. Gupta · H. Bherwani CSIR-National Environmental Engineering Research Institute, CSIR-NEERI, Nagpur 440020, India R. Kumar (B) Council of Scientific and Industrial Research (CSIR), Anusandhan Bhawan, 2, Rafi Marg, Sansad Marg Area, New Delhi 110001, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Goel and G. Sen (eds.), Climate Action and Hydrogen Economy, Green Energy and Technology, https://doi.org/10.1007/978-981-99-6237-2_3

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• Potential benefits of using green hydrogen • Policy roadmap to make India global hub of green hydrogen Keywords Climate change · Fossil fuels · Green hydrogen · Net zero emissions · GHGs

Abbreviations ATR CCS CCUS CEN CENELEC FMEA GWh GHG HAZID HAZOP IOCL ISV IEA IEC ISO Kg/m LOHC LPG MNRE NITI NDC POX QRA RA R&D SR TWh USD VRE

Auto-Thermal steam Reforming Carbon Capture and Storage Climate Capture Usage and Storage European Committee for Standardization European Committee for Electrotechnical Standardization Failure Modes and Effects Analysis Gigawatt-hour Greenhouse Gas Hazard Identification Hazard Operability Analysis Indian Oil Corporation Limited Identification of Safety Vulnerabilities International Energy Agency International Electrotechnical Commission International Organization for Standardization Kilogram/meter Liquid Organic Hydrogen Carriers Liquid Petroleum Gas Ministry of New and Renewable Energy National Institution for Transforming India National Development Council Partial Oxidation Quantitative Risk Assessment Risk Assessment Research and Development Steam Reforming Terawatt-hour United States Dollar Variable Renewable Energy

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1 Introduction Climate change is one of the most challenging issues of our time. It presents formidable obstacles to both communities and the environment [1]. There are different types of risk which has been arisen from the climate change, i.e. physical risk, transition risk, litigation risk, and reputation risk as briefed in Fig. 1. Physical risk can either be long-term and gradual or short-term also known as stochastic. Transition risk comes as a result of the transition to net-zero economy which includes things like new laws or regulations that require a disclosure or changes in business activity to address climate change. Litigation risk encompasses legal battles over cost allocation for climate change adaptation. Reputational risk, on the other hand, arises from consumer boycotts and can cause sales losses due to poor climate change performance. Physical risk poses a threat of substantial uninsured and insured losses for both homeowners and businesses, thereby translating into financial stability risk as shown below in Fig. 2 [2]. The impacts of climate change transcend borders, encompassing the entire globe with a magnitude unparalleled in its uniqueness [1]. Anthropogenic greenhouse gas emissions will evidently further increase global warming and changing climate patterns. Heightened by pollution, overexploitation of natural resources and degradation of environment will lead to severe, persistent, and possibly irreversible changes for humans, resources, economies, and ecosystems around the world. Various factors, encompassing the utilization of fossil fuels, contribute to the phenomenon of climate change through the emission of CO2 into the atmosphere, resulting in a rise in global temperatures and ultimately leading to the occurrence of climate change. If substantial measures are not taken at present, the task of adapting to these repercussions in the future may pose greater challenges and incur higher expenses [2]. Therefore,

Fig. 1 Type of risk arising out of climate change (Source Courseera.org) [3]

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Fig. 2 Translation of physical risk into financial stability risk (Source Courseera.org) [2]

climate change mitigation is necessary to reduce and avoid the worst effects of climate change. All together climate change adaptation is necessary to reduce susceptibility to the climate change impacts that we cannot prevent. In 2015, nations around the world came together and signed the Paris Agreement on Climate Change. This was a commitment of almost 200 nations to avert the worst effects of climate change by holding global warming to no more than 2 °C above pre-industrial levels. But the Paris Agreement contained an aspirational goal that it would be even better to pursue efforts to limit the temperature increase to 1.5 °C above pre-industrial levels in order to prevent the worst effects of climate change. Many organizations around the world have adopted models that look at the current state of the global economy where global greenhouse gas emissions are coming from and what needs to change between now and the year 2050 in order to get to net zero. Intergovernmental Panel on Climate Change as well as the International Energy Agency also targeted to achieve net zero by 2050 and limit warming to 1.5 °C or less. CO2 emissions linked to energy account for two-thirds of worldwide greenhouse gas (GHG) emissions. Global net anthropogenic CO2 emissions must decline by about 25% by 2030 from 2010 levels, before reaching net zero by 2070, to have a fair chance of remaining temperature below 2 °C by 2100 [4]. On 14 July, 2021, the European Commission adopted a set of proposals to make the EU’s climate, energy, transport, and taxation policies fit for reducing net greenhouse gas emissions by at least 55% from 1990 by 2030 [5]. The commission further stated that achieving these emission reductions is critical for Europe becoming the world’s first climate-neutral continent by 2050 and making the European Green Deal a reality. Carbon sequestration is imperative to attain net-zero emissions, requiring the offsetting of all worldwide GHG emissions. By the year 2100, the average global temperature is projected to soar by 3.5 °C. Nevertheless, a resolute dedication to achieving global net-zero emissions by 2060 may curtail the temperature increase to 1.5 °C by the end of the century. Research indicates that the global number of vehicles employed for transportation is predicted to quadruple by 2050, surpassing a staggering 2.5 billion. Despite global initiatives and agreements, global emissions

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are at record high due to increased energy demands along with little progress by humanity to address climate change [1, 4]. Through the initiative taken by government “Aatma Nirbhar Bharat Abhiyaan”, India is making efforts alike “build back better” in dealing with the ongoing crises which are interlinked. Through this initiative, the financial rescue packages to aid the country out of the COVID-19 crises are linked to a holistic societal development, where economic growth and prosperity is seen in relation to combating climate change, dealing with the environmental crises and making India self-reliant. In a post-pandemic world, it is evident that the Indian government is committed to embracing green energy and sustainable mobility as crucial drivers for rapid economic growth. Presently, India relies on petroleum and industrial-grade coal imports to meet its energy demand. However, this dependence on fuel imports and the uncertainties of commodity markets have the potential to hinder progress. Fortunately, India possesses ample renewable energy resources, although tariffs for power generated from these sources are declining [1]. Hydrogen plays a vital role as part of the multifaceted puzzle of a green energy transition. India, positioned as a global frontrunner in renewable energy production, possesses an unparalleled opportunity to spearhead the advancement of a worldwide hydrogen economy. The estimated potential for renewable energy generation in the country stands at a remarkable 1097.465 GW [6]. Remarkably, India has dedicated over USD 70 billion to the development of renewable energy in the past seven years, comprising 1.89% of the total investments received across various sectors within the same timeframe [7, 8]. India developed its first roadmap for Hydrogen and Fuel Cells in 2006. Although this process led to increased R&D activities in hydrogen-related areas, the road map was not followed up with actual pilot/demo projects. Today, Europe and the USA are moving fast on hydrogen initiatives and projects, and Japan, Australia, and Korea are closely following those who are ahead. With the defined framework of proposed National Hydrogen Energy Mission supporting India’s green energy initiatives with green hydrogen, several initiatives for hydrogen and associated projects are emerging in India. Strong voices are encouraging today for hydrogen both from the government and the private sector, providing a clear momentum. Now, the time is for implementing hydrogen as a key part of the energy system in India and the road ahead is materializing rapidly. In order to sever the connection between economic growth and the escalation of CO2 emissions, a profound transformation becomes imperative. The attainment of emission reduction goals necessitates a shift in the production and utilization of sustainable energy sources. Consequently, the ascendancy of green hydrogen (GH) power is swiftly emerging as a feasible substitute for fossil fuels and battery-operated mobility systems [1]. For climate experts, green or renewable hydrogen—made from the electrolysis of water powered by solar or wind—is essential to climate neutrality. It features in all eight of the European Commission’s Net-zero emissions scenarios for 2050. In theory, it has the potential to do three things: store excess renewable energy when the grid cannot handle it, assist in decarbonizing difficult-to-electrify sectors such as long-distance transportation and heavy industries, and replace fossil fuels as a zero-carbon feedstock in chemical and fuel manufacturing [9].

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Decarbonization of global energy system has been done through energy efficiency, behavioural change, electrification, renewables, hydrogen, hydrogen-based fuels, and CCUS. In the net-zero emissions scenario, the importance of hydrogen is reflected in its increasing share in cumulative emission reductions. Strong hydrogen demand growth and the adoption of cleaner technologies for its production thus enable green hydrogen-based fuels to avoid up to 3.6 Gt CO2 emissions between now and 2050 to contribute towards net-zero vision and climate risks [10].

2 Hydrogen Economy and Net-Zero Emissions In 1970, the idea of “hydrogen economy” was first introduced to describe using hydrogen as a fuel for the transportation sector at a time when oil prices were rising quickly. Now, the hold of the hydrogen economy is set as a tool for fighting climate change, by introducing replacement of fossil fuels in some of the hardest parts of our economy to decarbonize [11]. Fundamental changes are required presently to restrict global temperature rise below 1.5 °C which is a necessary climate action. A total of 81% of the world’s energy consumption today is based on fossil fuels, while renewable energy represents about 14.1%. The remaining energy, 4.9%, comes from nuclear power plants (IEA, 2018) [12]. The energy transformation involves a transition from fossil fuels to new value chains, based on renewable energy. Solar and wind power are the renewable energy sources that are most invested in. The characteristic of these energy sources is that the electric power produced varies due to changing weather conditions. It is stated in World Energy Transition Outlook 2021, that hydrogen and derivatives will account for 12% of final energy use by 2050. And further that “5000 GW of electrolyzer capacity will be needed by 2050, up from 0.3 GW today. In 2050, two-thirds of the total hydrogen will be green—produced with renewable electricity—and one-third blue, produced by natural gas coupled with carbon capture and storage (CCS)” [13]. It is reported that approximately 43 countries have now set up or are setting up either strategies or roadmaps for a hydrogen economy [10]. Compared to other renewable energy sources, hydropower represents an exception in its characteristics, as the water reservoirs represent the energy carrier and source of energy for the hydropower plants. Among the few countries, Norway is practically independent of alternative energy carriers in the energy system balancing the grid. The total production of hydropower in Norway is about the same as for the whole of India, approximately 150 TWh per year [8]. In India it is expected that the hydropower potential is about triple of current utilization (kept within 60% of total utilization), which will be significant for balancing the power grid. Further, hydropower development in India is facing major opposition from environmental safeguards groups who have highlighted the high cost to the ecosystems and natural riverine system [14].

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Fig. 3 Total primary energy demand in India (Source IEA (2021), India Energy Outlook 2021) [15]

India should adopt hydrogen economy because it will boost her energy security and lessening GHGs and to meet its commitment towards Paris Agreement. Continuous and sustained industrialization and urbanization in India is placing enormous demand on the country’s energy industry and policymakers where the per capita consumption of energy in India is far below than the world average and significant disparities were observed in India with respect to energy consumption and service quality within states (rural and urban areas). Majority of energy demands in India are provided through coal, oil, and biomass. Since 1990, these sources have regularly supplied more than 80% of India’s overall energy needs, among which coal is serving as preferred fuel for various sectors and presently provides 44% of India’s fundamental energy needs since 2000 as shown in Fig. 3. The industrial sector of India has been the primary driver of rising energy demand since 2000 [15]. Energy consumption in transportation sector has increased by 3.5 times, while building energy demand has climbed by 40%, owing to increasing appliance ownership and improved access to contemporary cooking fuels. Oil consumption has more than doubled due to rising vehicle and road transportation use since 2000 [16]. The increased usage of electrical motors and other machinery by industries has also contributed to the rise in electricity demand. Current installed electricity generation capacity in India is 382.73 GW, which is greater than its peak demand of 182.55 GW as of April 2021, as shown in Fig. 4 [6]. But this excess majorly goes to losses and infirm capacity in terms of renewables. According to the Fig. 4, total thermal power generation (includes coal, lignite, gas, and diesel) is 234.72 GW, which is much more than peak consumption. The total installed capacity of renewable energy sources is 95.013 GW, which includes biomass gasifiers, biomass power, urban and industrial waste power, solar, and wind energy [16]. Nuclear energy accounts for around 2.4% of India’s total electricity generation. As of 30 April 2021, renewable energy accounts for 12.2% of the national annual generated units.

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Fig. 4 Total electricity generation capacity in India (Source CEA, 2021) [17]

The power consumption in various sectors is depicted in Fig. 5, which shows consumption of electricity in 2019–20 of 12, 91, 424 GWh with compound annual growth rate of 6.74%. Due to a growing population, India’s energy usage has almost doubled since 2000 and the country is on track to become the world’s largest energy economy shortly [16].

2.1 Clean Energy-Based Economy of India Knowingly that aspirational renewable energy targets of India have gained much worldwide attention, coal is still found principal source of electricity, and the total projected coal reserves were found increased by 5.37% in 2020 compared to 2019 [18]. Despite the exceedance of installed capacity with respect to demand, India requires a secure supply of 3–4 times more energy than it consumes today, to meet the energy needs of such a rapidly rising economy. Furthermore, over 300 million people in India continue to lack access to electricity [19]. Therefore, India is gradually embracing ethical renewable energy technologies, reducing carbon emissions, cleansing the air, and assuring a more sustainable future.

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Fig. 5 Power consumption at various sectors (Source CEA, 2021) [17]

India’s energy balance has shifted away from traditional energy sources towards renewables. The total installed capacity of collaborative renewable energy generation increased by 11.19% in one year (2020) from 78.31 GW in 2019, as shown in Fig. 6 [6]. Wind power accounted for approximately 43.3% of renewable energy deployed generation capacity in 2020, supported by solar power, including rooftop solar (39.8%), and bioenergy power (11.2%). However, solar energy total capacity increased by more than 23% year on year from 2019 to 2020. In 2020, Karnataka state had one of the most installed capacities of grid-connected renewable energy (15.23 GW), followed by Tamil Nadu (14.34 GW), primarily from wind and solar power [19].

Fig. 6 Total installed capacity of interactive renewable power by type (MW) (Source MNRE, Energy Statistics India, 2021) [17]

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Fig. 7 Expected renewable energy potential source-wise (Source Energy Statistics India, 2021) [17]

India, which is known as one of the world leaders in the production of renewable energy, is in a unique position to take a lead role in the development of a global hydrogen economy where there is an extensive potential for the generation of renewable energy from various sources, including solar, wind, biomass, small hydroelectric power, and biogas cogeneration as indicated in Fig. 7 [20]. Over the past seven years, India has made a commendable investment of over USD 70 billion in renewable energy, accounting for 1.89% of the total investments received across various sectors in that period [7, 8]. By 2035, the proportion of renewable energy is projected to surge from its present level of approximately 27% to an impressive 51%, with further growth expected to reach approximately 73% by the year 2050 [20]. India needs a clear national renewable energy policy as well as a legal structure to meet the strategic goals. Also, funding for renewable power projects needs to be enhanced. As a result, incorporating renewable energy into India’s power grid will demand a change in planning and governance systems. (NITI Aayog Report, 175GW by 2022). In the NITI Aayog report, members propose policy ideas for meeting future demand forecasts with renewable energy contributions (Legislative and policy framework should be modified and updated; establishment of national renewable energy targets; incorporation of green hydrogen in the energy mix; financial support aimed at lowering incremental cost of RE). India recently set an aggressive goal of 500 GW of renewables capacity, one billion tonne reduction in cumulative emissions by 2030 [10]. According to Ministry of New and Renewable Energy’s year end evaluation (2020), 167 GW of renewable power projects has been installed (completed or under construction). The energy economy of India can be reimagined and transformed with the help of renewables and clean energy products such as green hydrogen. In a recent study, the Global Hydrogen Council has suggested that considering the cheaper tariffs of renewable energy, India is poised to become a net exporter of green hydrogen and will march towards the ambitious target of 500 GW and to meet this demand the system will need to be significantly more flexible with additional storage and grid investments, a larger

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focus on demand-side activities and bids that suitably compensate for system flexible services [10]. As per NITI Aayog Report, global demand for hydrogen could grow by almost 400% by 2050 by declining prices of hydrogen and seeing the growing urgency for decarbonization, led by industry and transportation. In 2006, realizing the importance of hydrogen as a fuel, India developed its first roadmap for hydrogen, and MNRE has been undertaking a broad-based research and development programme on different aspects of hydrogen and fuel cells. Recently in Budget 2021–22, Government of India launched National Hydrogen Energy Mission 2021–22 to generate hydrogen from renewable sources. In Feb 2022, a green hydrogen policy has been framed by Govt. of India for compliance/implementation by all the concerned stakeholders [21]. Although this process led to increased R&D activities in hydrogen-related areas, the roadmap was not followed up with actual pilot/demo projects. Today, Europe and the USA are moving fast on hydrogen initiatives and projects, and Japan, Australia, and Korea are closely following those who are ahead. Hydrogen’s potential growth in the global energy mix is remarkable, with projections indicating a significant rise from 2% in 2018 to an estimated 13–24% by 2050, demonstrating a robust compound annual growth rate (~8% CAGR) at the midpoint. Additionally, a substantial investment of USD 150 billion is predicted by 2030. Hydrogen’s benefits extend beyond carbon dioxide conversion, encompassing the conversion of biomass and waste plastics into invaluable fuels and chemicals, effectively contributing to the realization of a net-zero economy [1, 22]. A hydrogen economic system also improves air quality, mitigates carbon emissions, and fulfils the Atmanirbhar Bharat vision. Notably, it is imperative that GH assumes a pivotal role in the decarbonization of India’s economy, particularly in the challenging-to-decarbonize sector. India’s GH mission aims to expedite its strategies for producing carbon-free fuel from renewable sources, aligning with the government’s objective of achieving energy self-sufficiency by 2047. It is projected that by 2050, a significant majority of hydrogen production, amounting to three-fourths, will be derived from green sources, specifically through the use of renewable electricity and electrolysis [1].

3 Production of Hydrogen This is fact towards hydrogen being able to take on the role as the most important energy carrier in linkage with renewable energy over a longer period of time. The hydrogen production technology based on raw material can be categorized as conventional or renewable. In conventional technologies, the hydrogen is generated from fossil sources like natural gas, coal, oil, etc., and includes methods of hydrocarbon reforming (viz. Steam Reforming (SR), Partial Oxidation (POX), Auto-Thermal steam Reforming (ATR)) and electrolysis (Fig. 8). In consequence, the energy source and the production process will determine whether the generated hydrogen will be labelled as grey, namely blue; green; pink; or yellow as shown in Fig. 9.

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Fig. 8 Production process and storage methods of hydrogen (Source Adapted from: Salvi, B. L., & Subramanian, K. A. (2015). Sustainable development of road transportation sector using hydrogen energy system. Renewable and Sustainable Energy Reviews, 51, 1132–1155) [23]

Fig. 9 Types of hydrogen based on energy source and production process (Sources https://3degre esinc.com/resources/hydrogen-production-exploring-various-methods-climate-impact/) [24]

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The process of steam reforming biomass, biogas, bio-oil, or natural gas results in the production of blue hydrogen in conjunction with CO2 . Blue hydrogen effectively captures around 90% of the carbon through a technique known as carbon capture utilization and storage (CCUS), thus exhibiting a relatively modest carbon intensity [1]. The execution of CCUS aims at significantly reducing the emission rate of GHG and its effect on global warming and climate change. The steam reforming of fossil fuels, which is the dominant route now, gives grey hydrogen with cogeneration of CO2 , which is no longer acceptable. Hydrogen which comes from coal gasification is “brown” hydrogen, and “pink, red and purple” are common colours referring to hydrogen, which is produced when the electricity comes from nuclear power, while yellow is a newer phrase for solar-powered electrolytic hydrogen [25].

3.1 Production of Green or Renewable Hydrogen Hydrogen produced from electrolysis of water using renewable-driven energy sources, such as solar, wind, hydro, or nuclear, called as green or renewable hydrogen which produces zero GHGs. But due to the changing nature of the source of energy (sun and wind), fossil energy systems are still required as backup. The transition of energy may go from grey through blue to green hydrogen to achieve the decarbonization of the system and contribute to regional, national, and global climate targets (Fig. 10) [8]. The electrolyser market is expected to reach gigawatt-scale in 2022 spurred by increasing installation in China. Almost 40 GW of electrolysers by 2030 are already proposed. There could be significant increase if an aggressive green hydrogen price decline allows for the replacement of blue hydrogen with green hydrogen. However, today the cost of hydrogen from electrolysis is relatively high in India between around $7/kg and $4.10/kg depending on various technology choices and the associated easy-going costs [10]. The different technologies for power-to-hydrogen production will play an important role to meet those climate targets. Government and industry need to keep looking at any potential technology enabling environmentally friendly and cost-efficient hydrogen production.

4 Hydrogen Usage and Market Sectors 4.1 Export and Storage of Hydrogen Storage of hydrogen depends on its state (solid, liquid, or gas) which will be achieved by a combination of temperature and pressure. The hydrogen will be in its solid state at temperature below −259 °C (70.6 kg/m of volumetric density: mass of hydrogen stored by volume unit of the system) while it will be in a liquid state at −253 °C

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Fig. 10 Indicative production of hydrogen from natural gas, biomass, and electrolysis using renewable power (Source Reigstad, G. A., Coussy, P., Straus, J., Bordin, C., Jaehnert, S., Størset, S. Ø., & Ruff, B. (2019). Hydrogen for Europe-Final report of the pre-study. SINTEF Rapport.) [26]

(70.8 kg/m) and gas at 0 °C (0.09 kg/m), 1 bar of pressure. Storage of hydrogen in gas or liquid form can be done physically. Methods of physical storage constitutes compressed (high-pressure), liquid (cryogenic), and cryo-compressed tanks. Alternatively, storage of hydrogen can be done by using materials also. This process consists of either chemical storage (absorption within the material) or physisorption (absorption on the material surface). Although hydrogen gas compression is the most widespread method used to store hydrogen. This method allows higher volumetric hydrogen storage density compared to gas compression, although the tank must be thermally well isolated and stay under vacuum conditions. It implies a high cost of materials among other difficulties related to long-term storage periods (boil-off issue) and the energy needed for the liquefaction of hydrogen gas. Storage of hydrogen in in materials (e.g. ammonia) provides a good volumetric density, although its gravimetric hydrogen storage density is quite poor. Currently, technology of hydrogen storage is at different levels of development. However, for making hydrogen economy viable, storage of hydrogen needs further improvements in terms of material properties, storage capacity, efficient hydrogen storage, energy density, safety, and investment cost. Transportation and distribution of hydrogen is a very significant step in the use and implementation of the hydrogen economy. Transportation of hydrogen can be done in its gas (natural gas by high-pressure tube trailers; compressed hydrogen by truck, railcar and ship) or liquid form (by truck and ships in cryogenic tanks). Use of existing natural gas infrastructure to transport and distribute hydrogen as a blend is a viable low-cost approach especially in the initial stage of hydrogen economy [22]. Transportation and distribution of hydrogen will depend on where the hydrogen is produced and its demand at the point of end use. By 2030, roughly 30% of the announced production capacity will be transported, either through ships or pipelines. Ammonia, LOHC, and liquid hydrogen are the main considered vectors for export of long-distance hydrogen [19].

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4.2 Utilization of Hydrogen in Global Market The hydrogen market (feedstock) had an estimated value of USD 115 billion in 2019 and was expected to grow by USD 45 billion by 2022 [27, 28]. It is reported that clean hydrogen could help abate seven gigatons of CO2 emissions annually by the year 2050, which is about 20% of human-driven emissions if the world remains on its current global warming trajectory. Relating other technologies (renewables and biofuels), hydrogen has the potential to decarbonize different sectors, viz. industries, long range mobility, maritime shipping and aviation, and building heating. It is also used for viable and long-term storage power grids. It is reported that industry and transportation account for most of hydrogen’s abatement potential, which has a cumulative emissions reductions upside of 80 gigatons of CO2 through 2050 [3]. Hydrogen technologies proved remarkably robust during the COVID-19 pandemic, with their momentum behind hydrogen remained strong over the past year as shown in Fig. 11. It was a record year in policy action and low-carbon hydrogen production, with ten governments around the world adopting hydrogen strategies. It is reported that on the supply side, manufacturing capacity of supplier has doubled since last year, reaching 8 GW per year and with the understanding of all the projects in the pipeline could lead to an installed electrolyser capacity of 134–240 GW by 2030, twice the expectation from last year [29]. Moreover, low-carbon hydrogen demand for new applications remains low, limited to road transport only. Therefore, more efforts are needed in demand creation and in reducing emissions associated with hydrogen production. Mostly hydrogen is produced using natural gas for use in refineries and fertilizers [30]. Limited activities has been seen in the utilization of hydrogen for the energy transition. Presently, there are very limited activities in terms of the hydrogen-producing

Fig. 11 Global hydrogen demand by sector in the net-zero scenario, 2019–2030 (Source IEA, Oct, 2022) [12]

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system’s engineering input and trials/demonstration infrastructure in large numbers. On-site hydrogen generation units (reformers) operating on commercial fuels such as LPG, methanol, or natural gas are not available in the country, restricting the technology development process [31]. The activities summary is listed in the report “India Country Status Report on Hydrogen and Fuel Cells” by the Department of Science and Technology, India, in 2020 [16]. Hydrogen mostly in India today is produced via steam methane reforming and is mainly used in the fertilizer and refinery sectors. Indian Oil Corporation (IOCL) located in India has a wealth of experience in hydrogen production in the production techniques, including hydrogen from biomass, methane reformation, electrolysis, and photolysis (photoelectric water splitting). Prototypes have been developed and demonstrated at laboratory scale, which include bio-hydrogen production using distillery wastes; proton exchange membrane-based electrolysers for hydrogen production through the splitting of water and water–methanol mixture; methanol-reformer for production of hydrogen; hydrogen catalytic combustion cookers; hydrogen-fuelled internal combustion engines for stationary power generation, etc.

4.3 Green Hydrogen: Climate-Friendly Energy Solution Hydrogen can consider to be an ideal green fuel seeing it being the universe’s most abundant element. This clean energy is extremely adaptable, as it may be utilized as a gas or a liquid, transformed into fuel, power, or heat, and produced in a variety of ways. As mentioned, hydrogen cannot only aid India in meeting its Paris Agreement emission targets, but can also reduce its dependence on fossil fuel imports. Hydrogen is a multipurpose energy carrier that may be formed from a variety of sources and offers a wide range of long-term energy storage options. Hydrogen can be compressed, liquefied, or stored in solid or liquid form if it is used for fuel cells, turbines, or internal combustion engines. Hydrogen from renewables can be formed in a variety of ways, the most well-known of which is splitting water into hydrogen and oxygen in an electrolyzer using renewable energy. It is very reliable and can produce ultrapure hydrogen in a non-polluting manner when the electrical source is renewable energy. Hydrogen is a key input in fertilizers, refineries, and cement, so green hydrogen would help these industries cut aggregate emissions. It could also be used in steel manufacturing to reduce emissions by replacing the use of coal as the energy source and as a reducing agent [32]. It is targeted to propose world’s largest electrolysis (GH generation) capacity of over 60 GW/5 million tonnes by 2030 for domestic consumption which will help India to meet the 500 GW renewables target [10]. GH can help decarbonize sectors such as shipping, residential, and transportation (trains, shipping, and aviation application), where it can be used as a fuel [32]. The most cost-efficient approach to achieve decarbonization of the container shipping by 2030 is the use of clean ammonia as fuel. By 2050, hydrogen could also be used to

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produce synfuels (obtained from syngas which is the combination of hydrogen with carbon monoxide) for aviation and maritime transport. GH can be used in manufacturing industries such as steel and chemicals, where it can constitute an important raw material as well as a fuel. It could replace fossil fuels in power generation and be used to store renewable energy. As per the updated NDC, India now stands committed to achieve about 50% cumulative electric power installed capacity from non-fossil fuelbased energy resources by 2030. In 2050, up to 15% of the electricity produced will first be transformed into hydrogen and converted back to electricity when needed. A recent report from the Hydrogen Council reveals that from a total cost ownership perspective, about twenty-two hydrogen end-use applications can be the most competitive low-carbon solutions including hydrogen production, distribution, and retail costs. Further, green hydrogen could be used in gas turbines, along with ammonia, to manage fluctuations in the demand and supply of power. Hydrogen is a zero-emission alternative for heating because it may be burned in hydrogen burners or used in fuel cells. In the present era, hydrogen is used in low grade heat applications including process heating and drying. It is aimed to generate eco-friendly ammonia for exports by 2030, supporting India’s partners in their decarbonization efforts. Achieving this goal might necessitate a capacity of up to 100 gigawatts of renewable hydrogen [8]. The sectors of steel and iron are among the world’s most polluting sectors that account for 7% of global greenhouse gas emissions. Steel which is used majorly from bridges to cars is projected to contribute 35% of India’s CO2 emissions from fossil fuel combustion and industry by 2050, as per a report by The Energy and Resources Institute, making it the industrial material with the biggest climate impact. Radical changes are needed in iron and steel production technology to make the process sustainable and carbon neutral, the International Energy Agency said in a 2020 report [32–34]. Significant reduction of its carbon footprint is imperative for the steel industry to contribute towards mitigating global warming, a target efficiently fulfilled through the adoption of green hydrogen [20]. By 2030, the ambitious goal is to achieve a staggering production capacity of 15–20 million tonnes, making it the world’s largest producer of green steel and propelling this sustainable metal into the global mainstream [8]. The collective value of the GH market in India has the potential to reach $8 billion by 2030 and $340 billion by 2050. Furthermore, the electrolyzer market is projected to grow to around $5 billion by 2030 and an impressive $31 billion by 2050 [8]. Considering the expected price decline, analysis suggests that under an optimistic projection the cost of green hydrogen has the potential to decrease to around $1.60/ kg by 2030 and $0.70/kg by 2050 [8].

4.4 Safety and Regulations GH poses a grave risk due to its highly hazardous and combustible nature, demanding rigorous safety measures to avert potential leaks and explosions. The eventual release

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of hydrogen in enclosed areas commonly accessed by motor vehicles presents a notable peril (A study on the effectiveness of a ventilation system, International Journal of Energy Research, 2021) [1]. Codes and standards defined for hydrogen are critical in current industrial-scale hydrogen technologies. As newer applications such as marine, rail, and heavy-duty vehicles emerge, additional efforts in all aspects of safety, codes, and standards are required to address the needs specific to each application. In addition to rules and regulations applying to technical solutions, regulations should also be considered for the training of personnel who will work with hydrogen or hydrogen-based solutions throughout the entire hydrogen value chain. Standards are made available for using hydrogen by global standardization bodies (ISO, IEC) or regional ones (e.g. CEN: Comité Européen de Normalisation, English: European Committee for Standardization; CENELEC: French: Comité Européen de Normalisation ÉLECtrotechnique; English: European Committee for Electrotechnical Standardization). For ISO, the Technical Committee 197 “Hydrogen Technologies” has the leading role for standards development in the field [8]. A well-implemented safety culture on operators and users must be amplified by a high focus on product safety from the designers and manufacturers, which, in turn, will substantiate that the products being supplied to the market feature a high degree of intrinsic safety. This will depend on sound Process Safety Management throughout the lifetime of hydrogen systems by using well established industrial methods for Identification of Safety Vulnerabilities (ISV), identification of hazards and risk assessment (RA) such as hazard identification (HAZID); hazard operability analysis (HAZOP), failure modes and effects analysis (FMEA), quantitative risk assessment (QRA) among others.

5 Challenges to a Hydrogen Transition The main reason why the implementation of hydrogen technology is relatively slow is that it is very costly in the early phase, where upscaling must take place at all stages of the value chain. The production cost associated with hydrogen using renewable power and scaling up including equipping with CCS are challenges to overcome. The authorities need to play along with the business community based on a clear, predictable, and long-term action plan, which embraces a comprehensive energy transformation, financing, security, and regulatory framework conditions. The IEA estimates that meeting today’s hydrogen demand through water electrolysis would require 3,600 TWh a year, or more than the EU’s entire annual electricity production [35]. Renewable energy, crucial in generating GH via electrolysis, entails higher production costs, thereby rendering hydrogen more expensive to acquire [1]. Renewables prices observed incredible declines over the past years, and economic criteria is expected to drive further decrease. As the electrolysis technology matures and volume production and deployment take place, the cost of electrolyser will decline which in turn made the green hydrogen production economical.

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Another relevant challenge is that more than 80% of the world’s energy consumption is represented by fossil energy. For this very reason, companies and nations that own 80% of energy turnover naturally see it as challenging to quickly change expertise, technology, and business models to tomorrow’s energy system. Also, there are certain sectors like industry and heavy transport that are hard to decarbonize using the current low- or zero-carbon technologies. Moreover, as discussed above, transporting and storing hydrogen remain a big challenge and will require massive investment in infrastructure upgrades. Traditionally, minimal policy support has been seen for hydrogen from governments across the globe so far. Policy push has been towards other technology options and end uses, even when hydrogen can make a much bigger impact. Lastly, standards around hydrogen use either do not occur or have not been restructured.

6 Conclusion and Key Takeaway 6.1 Conclusion Climate change is nowadays most pressing matter causing significant challenges to the environment and the society primarily occurring due to anthropogenic activities. It is necessary to take mitigation measures to reduce and avoid climate change impacts. GH can play a vital role in energy transition of India with the potential to reduce emissions and enhancing competitiveness of industries in an increasingly decarbonizing world, boosting economic development, and improving public health and quality of life. Long-term strategy is needed to strengthen the hydrogen market. Facing the high cost and lack of supporting technologies and infrastructure, government have number of challenges in paving the way for this new kind of energy. Decreasing the cost and enhancing the renewable electricity along with massive investment in infrastructure and manufacturing and technology improvements in electrolysers will bring down the cost of GH in the near future and making it viable and economic with existing technologies present. The Indian government needs to advocate policy actions, industry players, and financial institutions for fast penetration of hydrogen. It is significant to establish the framework for a long-term collaboration between the authorities, the R&D communities, and the business community. Standards and regulations around hydrogen production and use should be revisited, and implementation of new regulations and standards should be prioritized to enable a quick transition to a hydrogen economy. India has a unique opportunity to become a global leader in the hydrogen energy ecosystem. With proper policy support, industry action, market generation and acceptance, and increased investor interest, India can position itself as a low-cost, zero-carbon manufacturing hub, at the same time fulfilling its goal of economic development, job creation, and improved public health.

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6.2 Proposed Initiatives to Make India Global Hub of GH The study and discussions presented in the above chapters highlighted India’s opportunities to use GH for decarbonization, manufacturing, and exports. Further actionable recommendations which may lead to a National Action Plan on GH to enhance National Hydrogen Mission are as follows: 1. Development of policy direction in the form of a national roadmap focussing on all aspects of GH which will improve confidence of investors and meet the entire value chain and various associated agencies towards a singular vision. 2. India should aim to build manufacturing support of electrolyzers of capacity 25 GW by 2030 and investing $1 billion in R&D to catalyze the development of viable green hydrogen technologies across the value chain. 3. Reduction in cost of GH via waiver of interstate transmission charges, grant of open access for GH, reduction in taxes and surcharges, preferential dollarbased electricity tariff, revenue recycling of any carbon tax, low-emission power purchase agreements (PPAs), and avenues for firming electricity supply including discounted grid electricity to complement variable renewable energy (VRE) generation. 4. Provision of GH production linked incentives for new applications and clear mandates around hydrogen blending in existing and potentially future consumption sectors to achieve GH production capacity of 160 GW. 5. Development of GH standards and a labelling programme keeping in mind the widespread use of GH across sectors. 6. Exploring integration of green hydrogen and green hydrogen rooted products (green steel and green ammonia) into existing energy and industrial partnerships globally. The government should explore specific near-term incentives around green ammonia and green steel production. 7. The government can provide financial certainty to early adopters through investment facilitation measures like demand aggregation, ensuring availability of long-tenor and low interest finance and initiation of a functioning carbon market. 8. States should be encouraged to launch their own green hydrogen-based policies in order to complement efforts at the national level. 9. Initiate appropriate and rapid skills development across the ecosystem including government, industry, and academia addressing technologies, business models, policies, and geopolitics. 10. The government should develop an inter-ministerial governance structure with globally trained experts to effectively implement the mission.

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The Net Zero Goal and Sustainability: Significance of Green Hydrogen Economy in Valorization of CO2 , Biomass and Plastic Waste into Chemicals and Materials Ganapati D. Yadav

Abstract Net zero is a massive plan to constrain the global temperature rise to less than 1.5 °C whereby annual GHG emissions must be reduced from ~36.6 Gt to less than 10 Gt by using non-carbon renewable energy sources. Green hydrogen will play a huge role in transforming C1 off gases like CO2 into valuable chemicals and materials. Both blue and green hydrogen will contribute about 24% in the renewables totaling to about 539 to 820 MMTA in 2050. (Waste) Biomass will be transformed into fuels, chemicals and materials using hydrogen and oxygen derived from water splitting. Waste plastic can be chemically recycled into several hydrocarbons and depolymerized into monomers using different techniques, and hydrogenation will be very effective in tackling plastic pollution. Hydrogen is a key component in converting waste to wealth. Green hydrogen is poised to be a savior of the world. The concept of CO2 refinery is discussed, and use of biomass and plastic waste toward hydrogen economy is described. Learning objectives: • • • • •

Significance of green hydrogen economy in achieving net zero Green ammonia and CO2 as future fuels for sustainability Chemical recycling approaches of producing fuel from waste and plastics Cost-effective green hydrogen production at the ICT, Mumbai, India

Keywords Net zero · Green hydrogen · Carbon dioxide valorization · Biomass transformation · Plastic chemical recycling · Waste to wealth

G. D. Yadav (B) Emeritus Professor of Eminence and National Science Chair (SERB/DST/GOI), Institute of Chemical Technology, Mumbai 400019, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Goel and G. Sen (eds.), Climate Action and Hydrogen Economy, Green Energy and Technology, https://doi.org/10.1007/978-981-99-6237-2_4

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Abbreviations BNEF CCCUS CCUS CCU CCS CO2 DME EG FT GI HFCO HMF HDPE HDC HDO HDS HDM HDN HTP ICT LDPE MDC MSW MI OEC PVC PET PUs PS PE PP RNG SNG SOEC SUP SSE WEC

Bloomberg New Energy Fund CO2 utilization as Carbon Capture Utilization and Storage Carbon Capture and Utilization and Storage Carbon capture, and utilization Carbon Capture And Storage Carbon Dioxide Dimethyl Ether Ethylene Glycol Fischer–Tropsch Glycemic Index Hydrogen and Fuel Cell Technologies Office Hydroxymethylfuran High-Density Polyethylene Hydrodechlorination Hydrodeoxygenation Hydrodesulfurization Hydrodemetallation Hydrodenitrogenation Hydrothermal Processing Institute of Chemical Technology, Mumbai, India Low-Density Polyethylene Methylene Chloride Municipal Solid Waste Mission Innovation ONGC Energy Centre Polyvinyl Chloride Polyethylene Terephthalate Polyurethanes Polystyrene Polyethylene Polypropylene Renewable Natural Gas Sustainable Natural Gas Solid-Oxide Electrolysis Cell Single Use Plastic Selective Solvent Extraction World Energy Council

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1 Introduction The world is running out of fossil energy and materials at an alarming rate which was not anticipated a few years ago. It is a result of excessive use and wastes. The concepts of circular economy and sustainable development were endorsed by all nations of the world, and collective efforts and policies were launched. The focus of this article is on how the waste can be converted into wealth be that GHG carbon dioxide, (waste) biomass not used as food and waste plastic of all kinds by using green hydrogen. The overuse of fossil carbon including crude oil, coal and natural gas during the past few decades is primarily responsible for the unprecedented emissions of carbon dioxide leading to climate change, global warming, floods and famines. The fossil carbon will all be exhausted in the foreseeable future bringing into picture the hunt for alternate sustainable resources for energy and materials. Global GHG emissions from fossil fuels and change in land use were responsible for emissions of 40 Gt CO2 equivalent 2021. Since the industrial revolution, and particularly after the discovery of petroleum reserves, several billion tons of carbon dioxide have been released into the atmosphere, and the concentration stands at 421 ppm (October 2022) with the USA being the topmost and China as the second largest emitters. India is way behind at the seventh position [1]. However, this will change in the near future as population rises, and demand for energy and materials increases disproportionately. The Paris Agreement of 2015 pledged that the nations of the world should restrict the global temperature rise to less than 2 °C and preferably below 1.5 °C by adoption of new technologies, energy efficiency and alternate sources, and thus, the plan for the net (carbon) zero emissions by 2050 was mooted [2]. In the COP26 held in Glasgow in November 2021, India committed to achieve the net zero goal by 2070 [3]. What is required is to promote carbon-negative energy supply to attain the net zero goal at a faster pace. It would be relevant to mention the Mission Innovation (MI), a global initiative of 23 countries, including the USA, China, Japan, the EU and Saudi Arabia, which is meant to fast-track the global clean energy innovation to provide an opportunity for CO2 utilization as Carbon Capture Utilization and Storage (CCUS). The annual rate of rise in atmospheric CO2 concentration over the past 60 years is about 100 times faster than previous natural increases [4]. Modern societies are all accustomed to the fossil carbon-based economy—luxury, comfort, longevity—which have revolutionized our lifestyle for more than a hundred and fifty years; however, alas, it has and will bring miseries too if we do not tackle the carbon dioxide emissions through technological interventions and innovations. The energy needs of the world are increasing day by day, and the use of carbon-based fuels will continue to rise. To follow the requirements of international treaties, the use of renewable resources is advanced. The European Union revised its 2030 targets of reducing carbon dioxide emissions from 40 to 55% below 1990 level to achieve the net zero-carbon goal by 2050. Whether the carbon is coming from fossil fuels, waste biomass, or biofuels,

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there is a dire need to convert carbon dioxide into fuels, chemicals and materials to make a net zero economy [5]. The world’s economies are heavily dependent on carbon [6]. It is predicted that by the middle of the twenty-first century, there may not be worthwhile petroleum reservoirs to be exploited economically by using the current methods of production, and hence alternate sources must be tapped for chemicals and materials, let alone energy [7, 8]. In the realms of renewable sources in 2050, 73% energy will come renewables: solar, wind, geothermal, hydro, nuclear and hydrogen [9, 10]. I believe in the carbon-negative scientific trinity: Solar, wind and hydrogen as green energy sources, among which hydrogen will be the savior of the environment and provide of chemicals and materials from waste carbon [10]. Both blue and green H2 will be part of the energy mix which will be about 25% by then [11]. Blue hydrogen is carbon neutral and not carbon-negative. The green hydrogen and green ammonia policy declared by the Power Ministry of Govt. of India in February 2022 has envisioned that 50% of India’s energy needs will be met by renewable sources. As regards carbon-based chemicals and materials, CO2 and (waste) biomass will be valuable sources if the hydrogen economy is adopted [12]. Not many realize that waste plastic is also an important source of energy, chemicals and materials and green technologies should be adopted and policies be in place to reduce the burden on the environment as well as to augment energy and material supply. Whether it fossil fuel or renewable carbon source the fate of the carbon is ultimately carbon dioxide which must be taken dealt with to reduce global warming (Fig. 1).

Fig. 1 Carbon conversion processes to manufacture useful products. Carbon has been solely responsible for advancement in life style, comfort, luxury, transport, instant communication and longevity [5] (Open access, copy right with author of this article)

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2 Hydrogen Production Technologies Hydrogen can be employed as a fuel in many applications, including fuel cell power generation and fuel cell vehicles. It combusts cleanly, producing only water. It is predicated that we will run out of oil by the mid-2050s and new renewable sources of energy and materials are required. As stated earlier, the renewable energy share will rise to ~73% by 2050 in total of 49,000 TWh [10, 11]; however, coal will still play a role meaning thereby the need to hydrogenate CO2 . Thus, hydrogen share could grow from 2% of the global energy mix in 2018 to 13–24% by 2050, at ~8% CAGR at the mid-point. An investment of USD 150 billion by 2030 is predicted by the Hydrogen Council [13] and the European Union [14]. In the net-(carbon)-zero economy, green hydrogen will not only achieve the objective of converting CO2 into fuels and chemicals, but also transforming (waste) biomass and waste plastics into fuels and chemicals. Thus, CO2 and hydrogen are connected in more than one way for protection of environment and provision of future stocks of chemicals and energy. Hydrogen can be produced by water splitting or from any carbon source, fossil or renewable using steam reforming or pyrolysis. Steam reforming is accompanied by CO2 emissions (Fig. 2). Hydrogen production technologies are generally categorized into three types (sometimes five) such as grey hydrogen, blue hydrogen and green hydrogen. Depending on the energy source and method, additional two categories are also mentioned in the literature such as turquoise and brown hydrogen. The major difference among the grey, blue and green hydrogen is that the hydrogen is produced using fossil fuels, non-renewable energy and renewable energy, respectively [10]. Electrolysis of water using clean electricity from wind, solar, hydro or nuclear energy sources or thermochemical inorganic water splitting cycles such as copper-chlorine or sulfur-iodine will produce green hydrogen with zero-carbon dioxide emissions. Steam reforming of virgin and waste biomass, biogas, bio-oil or natural gas also gives hydrogen called blue hydrogen utilizing the other carbon portion in the feedstock as carbon dioxide which must be captured, stored and used (the so-called CCUS). It is estimated that blue hydrogen process captures up to 90% of the carbon having low to moderate carbon intensity as given in Table 1 [10]. The currently practiced grey H2 is the steam reforming of fossil coupled with co-generation of carbon dioxide; this method is the most common technology which is increasingly unpalatable because of the emissions of carbon dioxide. In the turquoise method, methane pyrolysis is done to get hydrogen with the carbon produced as carbon and not CO2 . Brown H2 is produced from coal without CCUS. Table 1 presents a comparison and approximate cost of production for 100 TPD of hydrogen production. The green hydrogen production by using electrolysis of water is currently not economical but hotly pursued by major players and governments. Based on the information provided by the Hydrogen Council [13], the International Energy Agency (IEA) [15] and Bloomberg New Energy Fund (BNEF) [16], the following statistics should give an idea of the hydrogen economy.

Hydrogen Storage & Utilization

Water Splitting

Solar PV

Biomass

Geothermal

Wind

Fig. 2 Hydrogen production methods from different sources

Direct Solar

Renewable

Coal

Oil

Fossil Fuel

Hydrogen Storage & Utilization

C sequestration

Steam Reforming

Energy Input

Cracking

Natural Gas

Fossil

Radioactive waste

Hydrogen Storage & Utilization

Electricity for electrolysis

Nuclear

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Table 1 Merits and demerits of different hydrogen production processes Type of hydrogen

Brown

Grey

Torquise

Source

Coal

Natural gas

Natural gas Natural gas

Process

Steam reforming

Steam reforming

Pyrolysis

Steam Electrolyzer Cu-CI water reforming water splitting closed splitting loop

Products

No carbon capture and storage

No carbon capture and storage

Hydrogen and carbon as coproducts

Most carbon capture and storage

Ton of CO2 emitted per ton H2

19

11

O (solid C 0.2 as product)

0

0

Cost per kg H2 US$

1.2–2.1

1–2.1

1

3–7.5

0.95 (credit of 0.9 for O2 not considered)

Blue

1.5–2.9

Green

Green (ICT-OEC Process)

Renewable electricity

Themo-chemical

NoGHG O2 NoGHG. O2 as as coproduct coproduct

1. Electrolyzer costs: 1100 US$/kW (2020) to 550 USD/kW (2030), 220 USD/kW (2040). 2. The Institute of Chemical Technology (ICT)-ONGC Energy Centre (OEC) CuCl thermochemical process is predicted to produce hydrogen at less than a dollar per kilo for 100 TPD capacity (author’s own work on pilot scale). 3. Costs of CCS increases the costs of steam reforming of natural gas from 990 USD/kWh to 1850/kWh. 4. Low-carbon fossil-based hydrogen: Cost in 2030 from 2.5–3.0 USD in the EU. 5. Green hydrogen: USD 1.3–2.9/kg (Fig. 3). 6. Target for solar electricity is to be cost competitive with the current fossil-fueled system. 7. If the cost of installed PV power can be reduced from the present cost of about USD 5/W installed to about USD 1/W installed, the cost of solar electricity is predicted to reach USD 0.10/kWh.

2.1 ICT-OEC Green Hydrogen Production Process The ICT-OEC thermochemical Cu-Cl developed in this author’s lab is a closed loop process with energy supply from solar energy stored in molten salts [5, 10, 12]. On the contrary, the steam reforming of fossil carbon likewise gives grey hydrogen coupled with co-generation of carbon dioxide; this method is the most common

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Fig. 3 Hydrogen cost prediction of US department of energy [17]

technology used by many industries and it is cheap. However, it is gradually becoming unpalatable because of the CO2 emissions. All refineries use grey hydrogen in eight of their conversion processes releasing huge quantities of CO2 . Hydrogen and ammonia (which on catalytic splitting gives green hydrogen and nitrogen) are envisioned as the future green fuels to substitute fossil fuels such as crude oil, coal and natural gas. Hydrogen economy will be reality if the green hydrogen becomes as cheap as the grey hydrogen (Fig. 3). Currently the clean hydrogen cost is in the range of ~$2.50–$6.80/kg. The overall challenge to green hydrogen manufacture is its cost. US DOE’s Hydrogen and Fuel Cell Technologies Office (HFCO) is working on developing technologies that will produce green H2 at $2/kg by 2025 and $1/kg by 2030 via net zero-carbon routes, in support of the Hydrogen Energy Earthshot goal of reducing the cost of green hydrogen by 80% to $1 per 1 kg in 1 decade (“111”) [17]. The various applications of green hydrogen are presented in Fig. 4. It is claimed by Haldor Topsoe that their high-temperature solid-oxide electrolysis cell (SOEC) permits to generate carbon-free hydrogen or carbon monoxide using renewable electricity [18].

3 Green Ammonia While hydrogen has the benefit of high energy density on a mass basis, huge storage volumes needed, and limited existing infrastructure are viewed as a deterrent in the hydrogen economy. Therefore, ammonia was found to be a viable solution for transportation and storage of the fuel and crack it back to hydrogen at the user end. Industrial production of ammonia is done usually by the so-called Haber–Bosch process, in which nitrogen from the atmosphere is catalytically coxed with hydrogen under high temperatures and pressures. Ammonia manufacture across the world produces ~420 MMTA of CO2 , which together with hydrogen production, which accounts for 830 MMTA of CO2 ; thus it is totally about 2% of GHG emissions per

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Fig. 4 Applications of green hydrogen in energy sector, CO2 and biomass conversion

year. Green ammonia could make a substantial contribution to the decarburization of agriculture through additional sustainable production of fertilizers. It can also assist in power generation or as a clean fuel for transportation, largely to power ships. Because of the much higher density of ammonia and its higher energy content, green ammonia lends itself to all applications of green hydrogen (Fig. 5). The mass energy density of hydrogen is 120 MJ/kg vis-à-vis 18.6 MJ/kg for ammonia, hence its popularity as an alternative fuel. Although hydrogen is an energy carrier, the benefits of green ammonia might overwhelm those of hydrogen because ammonia are denser than hydrogen and needs to be compressed only to 10 atm or cooled to −33 °C to store energy. On the contrary, hydrogen must be compressed to 350– 700 atm or cryogenically cooled to −253 °C as a liquid. Since NH3 can be stored at lower temperatures, it is an ideal energy carrier. It is also suitable for storing and transporting energy from renewable energy sources [19]. Because ammonia is extensively used for fertilizers, there is already existing distribution network where ammonia is stored in large, refrigerated tanks and then transported by various means,

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Fig. 5 Synthesis and applications of green ammonia. Both water and air will be the feed stocks for green hydrogen and green ammonia

such as pipelines and water which is also an advantage and could be used for green ammonia in the fertilizers sector, or if extended also in other ways (Fig. 5).

4 Pitfalls of Fossil Carbon-Based Energy Economy Among all GHGs, carbon dioxide and methane are the principal constituents which contribute the most to the man-made GHG effect and climate change. Future processes or concepts that undertake this CO2 reduction must consider the life cycle to assure that additional CO2 is not released beyond what is already being removed from or going into the atmosphere. CO2 sequestration is widely documented as an important choice to reduce increasing levels of its concentrations. CCUS technologies are viewed as a practical solution that involves recycling of CO2 to various important industrial compounds, fuels and feedstock materials bringing to the core the synergism and innovations of catalytic chemistry, chemical engineering and technology, material science and biological sciences to alleviate climate change. However, CCUS technologies are criticized for permitting the continued use of fossil fuels. In addition to the coal-based power plants, steel industry releases more than 3 billion metric tons of CO2 each year, having the biggest climate impact. China is number one producer of steel, and India is second; one ton of steel emits 2.3 tons of CO2 . To restrict the global warming, the steel industry must reduce its carbon footprint totally and make use of green hydrogen to produce green steel. The same argument holds for other metal industries. Much attention has fixated on CO2 , but methane is a dominant and dangerous GHG. At the COP 26, over 100 countries signed up to the Global Methane Pledge to reduce global methane emissions by 30% by 2030. This includes six of the world’s topmost 10 methane emitting nations like the USA, Brazil, EU, Indonesia, Pakistan and Argentina and would account

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to a potential of 46% of global methane emissions and over 70% of global GDP, playing a critical role in keeping the goal of 1.5 °C rise within scope [3]. Among all the anthropogenic GHG, CO2 is largely responsible for global warming and climate change. The sustainability of extravagant lifestyle of modern society requires gigantic quantities of energy which is primarily satisfied by the fossil resources. The concentration of carbon dioxide in the atmosphere increased from 280 ppm before the industrial revolution to 421 ppm in October 2022 [1]. The increased atmospheric CO2 concentration is arguably one of the primary causes of accelerated climate change and global warming. This supply chain from fossil feedstock cannot sustain forever as all these energy sources will diminish within three centuries. From the economic point of view importing fossil fuel from foreign countries worth of billion dollars is a waste of foreign exchange for the marginal and developing economies having no oil reservoirs or coal deposits. For instance, a fast growing Indian economy imported 228.6 trillion tons of crude oil at US$ 130 B in 2020, and the government wants to reduce import of oil by developing new technologies including renewable resources such as solar, wind, hydro, coal to fuels and chemicals, 2G ethanol, and biodiesel. India accounts for more than a quarter of the net global primary energy demand between 2017–2040 according to BP Energy [6]; 42% of this new energy demand is met through coal, meaning CO2 emissions will roughly double by 2040. The Paris Agreement 2015 is meant to reduce the risk and impact of global warming by adopting two long-term temperature goals, i.e., to check the global average temperature rise well below 2 °C above pre-industrial level, and to take more deliberate actions to limit the rise in temperature to 1.5 °C above pre-industrial levels. To achieve this goal a 20/20/20 strategy was adopted, meaning thereby, 20% decrease in CO2 emission, rise in renewable energy market share by 20%, and 20% increase in efficiency of current technology which calls for research and innovation. The share of the renewable energy will increase from current ~27% to ~51% by 2035 to ~73% by 2050 totaling 49,000 TWh in which both green and blue hydrogen will have a substantial role [20].

5 Carbon Dioxide as the Future ‘New Oil’ Carbon dioxide is non-toxic, non-flammable and highly stable. Since it is produced by a number of power plants, refineries, fermenters and other industrial processes, which are all contributors to the GHG-related problems, CO2 should not be treated as a liability but a great feedstock for preparing commodity chemicals, fuels, and materials by using innovative cost-effective catalytic processes. Since CO2 is very stable, its activation is difficult requiring highly active catalysts. Carbon dioxide can be valorized while meeting the net zero goal and it will be the ‘new oil’. The future refiners will use carbon dioxide as a raw material for making fuels, chemicals and polymers/materials, where green hydrogen will be the most important reactant.

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As an economical, safe and renewable carbon source, CO2 turns out to be an attractive C1 chemical building block for making organic chemicals, materials and carbohydrates (e.g., foods). The utilization of CO2 as a feedstock for producing chemicals not only contributes to alleviating global climate changes caused by the increasing CO2 emissions, but also provides a grand challenge in exploring new concepts and opportunities for catalytic and industrial development. Decreasing CO2 concentration in the atmosphere while meeting the energy demands of an ever increasing population is a formidable task and requires long-term planning and implementation of CO2 mitigation strategies. Reduction of CO2 production by shifting from fossil to renewable fuels, CO2 capture and storage (CCS) and CO2 capture and utilization (CCU) are the possible areas for systematic control and reduction of atmospheric CO2. Carbon capture and utilization and storage (CCUS) is one of the key areas that can achieve CO2 emission targets while simultaneously contributing to the production of energy, fuels and chemicals to sustain the increasing demands. In CCU concept, CO2 is captured and separated from emission gases and then converted into valuable products. It is used to produce chemicals such as urea (75 million tons), salicylic acid, cyclic carbonates and polycarbonates [21–24]. As of now, numerous CO2 capture technologies related to physisorption, chemisorption carbamation, amine physical absorption, amine dry scrubbing, membrane separation and mineral carbonation have been practiced. Therefore, CO2 may turn out to be the future ‘new oil’ by catalytically converting it into synthetic fuels starting from the mixtures of carbon dioxide and hydrogen with specific multiphase reactors. In that way CO2 appears as one of the possibilities for high-level energy storage, including the network regulation from renewable energy production. But, in each case, novel catalytic processes and plants are needed to develop this future industry. Flue gases from fossil fuel-based power plants are the main concentrated CO2 sources. If CO2 is to be separated, as much as 100 MW of a typical 500-MW coal-fired power plant would be necessary for today’s CCUS based on the alkanolamines absorption technologies [25, 26]. Therefore, it would be highly desirable if the flue gas mixtures are used for vehicle CO2 conversion but without its pre-separation. CO2 conversion and utilization should be an integral part of CO2 management, though the amount of CO2 that can be utilized for making industrial chemicals is small vis-à-vis the amount of flue gas. Bulk chemicals routinely manufactured from CO2 include urea to make nitrogen fertilizers, salicylic acid as a pharmaceutical ingredient and polycarbonate-based plastics (Fig. 6). However, carbon dioxide can be catalytically converted into methane and higher hydrocarbons, methanol, dimethyl ether (DME), formic acid and other formates as proved in the author’s laboratory using hydrogen among researchers (Fig. 7). It forms a part of the hydrogen economy. CO2 also could be employed more widely as a solvent; for instance, the use of supercritical CO2 provides benefits in terms of stereo-chemical control, product purification and environmental factors for making fine chemicals and pharmaceuticals, for tertiary oil and gas recovery by CO2 flooding, enhanced agricultural production and ponds of genetically modified algae that can convert power-plant CO2 into

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Fig. 6 Carbon dioxide refinery: CO2 as a feedstock for making a variety of products

biodiesel [21, 22, 27]. The extraction of CO2 on gigantic scale including that from the atmosphere is a phenomenal task but it can be achieved by using novel catalytic technologies, process intensification and multiphase reactor design.

5.1 Flue Gas as Source of CO2 On the basis of the economic and environmental viewpoints, there seems to be a unique benefit of using flue gases directly, rather than the pre-separated and purified CO2 . Typical flue gas composition from natural gas-fired power plants could be around: 8–10 CO2 , 18–20 water, 2–3 oxygen and 67–72 nitrogen v/v %. Whereas a flue gas from coal-fired plants may contain 12–14 CO2 , 8–10 water, 3–5 oxygen

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Fig. 7 Carbon dioxide conversion to valuable commodity fuels and chemicals using green hydrogen developed in author’s lab by ICT-OEC technology [5, 12]

and 72–77 nitrogen v/v %. The furnace outlet temperature of flue gases is normally ~1200 °C which will fall gradually along the pathway of heat transfer, while the temperature of the flue gases exiting to the stack is ~150 °C. Pollution control technologies can eliminate SOx , NOx and particulate matter effectively, but CO2 and water as well as oxygen remain largely unaffected [28]. Some important chemistries using CO2 are given in Fig. 8. CO2 conversion into gaseous or liquid hydrocarbon requires high temperature (523–723 K) and pressure (20–40 atm), but the conversion is low due to problems in the activation of CO2 . Therefore, currently available technologies are not economically suitable for industrial application. Efficient heterogeneous catalysts can minimize the energy needed for reactions by reducing the activation energy. A lot of literature exists on the utilization of pure CO2 by different ways such as using plasma, photocatalytic system, electrochemical reduction and heterogeneous catalysis. [30–34]. A few attempts have been made to develop continuous processes for converting carbon dioxide from flue gas to value-added products that are economical and have the potential to meet energy and material needs of the future. However, hydrogen plays an important part in CO2 valorization and carbon sequestration. The reduction of CO2 emissions of ~40 Gt in 2021 to ~10 gigatons will contain the global temperature to within 1.5 °C by 2050 [11]. For hydrogen to contribute to mitigate climate change and climate neutrality, it must attain much larger scale of production, totally derived from water splitting using green technologies. The hydrogen economy must overcome many challenges including large-scale infrastructure for refilling stations of hydrogen, akin to those of petrol, diesel and natural gas, and the cost of hydrogen production, transport and storage must be low. These challenges can be surmounted collectively by multiple partnerships among companies, nations and research across institutions, and above all local government policies [13]. Green

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Fig. 8 Schematic representation of possible usage of CO2 for fuel and chemicals [21, 22, 29]

hydrogen must cost below 1.5–2 USD/kg to make the hydrogen economy a reality. Incidentally, the cost of hydrogen production by Institute of Chemical TechnologyONGC Energy Centre (ICT-OEC) hydrogen production technology, developed by this author using water splitting in conjunction with solar energy, is less than USD 1/kg [12]. One of the issues of using carbon-based technology, whether renewable or fossil, is the emission of CO2 which can be valorized by using hydrogen into a few chemical products such as methane and higher hydrocarbons, methanol, dimethyl ether (DME), formic acid, formates, carbonates, ammonia and urea. DME is the cleanest, colorless, non-toxic, non-corrosive, non-carcinogenic and environmentally friendly replacing CFC. DME can be effectively used in diesel engines. Like methanol, it is a cleanburning fuel and produces no soot and black smoke. DME is the best substitute for LPG as a cooking fuel, and the well-established LPG industry infrastructure can be used for DME [35–37]. Hydrogen can serve as a vector for renewable energy storage in conjunction with batteries, guaranteeing as a backup for season variation. Steelmaking releases more than 3 billion metric tons of CO2 each year, having the

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biggest climate impact. To help limit global warming, the steel industry will need to shrink its carbon footprint significantly. Thus, hydrogen can substitute fossil fuels in some carbon intensive industrial processes, such as steel, chemical and allied industries. It can present solutions for difficult to abate parts of the transport system, in addition to what can be accomplished through electrification and other renewable and low-carbon fuels.

6 Biogas as Source of CO2 Biogas, typically containing 50–75% methane and 25–50% carbon dioxide, is produced by anaerobic fermentation from almost all types of biomass, including wet biomass, (which is not usable for most other biofuels), vegetable and animal livestock waste, manure, harvest surplus, oil residues, municipal solid waste (MSW), etc. It is gaining significant industrial attention as a renewable source of carbon. Conventionally, after purification, biogas can be directly combusted for heat and electricity generation yet, and the heat value of such combustion processes is low due to the high concentration of CO2 in the feed gas. From an efficiency point of view, syngas production by biogas reforming with a H2 /CO ratio close to one is an appropriate option for the full utilization of both CH4 and CO2 in biogas for several industrial applications. Depending on the molar H2 :CO ratio in the reformed bio-syngas, it can be directly applied as a feedstock for the production of methanol, dimethyl ether (DME), long hydrocarbon chains via Fischer–Tropsch (FT) process or NH3 synthesis by the Haber route. Another incentive for using gaseous biofuels for transport applications is the prospect to diversify feedstock sources. Biomethane, also called renewable natural gas (RNG), or sustainable natural gas (SNG), which is separated from biogas, is the most efficient and clean-burning biofuel available today. Biomethane is upgraded to a quality like fossil natural gas, having a methane concentration of 90% or greater, by which it becomes possible to distribute the gas to customers via the existing gas grid within existing appliances. Furthermore, it is very promising to use biogas containing carbon dioxide as the co-reactant for methane conversion in the so-called dry reforming process [38], since carbon dioxide can provide extra carbon atoms for methane conversion, while carbon dioxide also serves as a better oxidant, compared to oxygen or air. The co-feed of carbon dioxide will also increase the methane conversion and the yield of objective product. However, the introduction of carbon dioxide into the feed will lead to a complex product. In addition to syngas, gaseous hydrocarbons (C2 to C4 ), liquid hydrocarbons (C5 to C11+ ) and oxygenates can be produced in methane conversion with the co-feed of carbon dioxide. The liquid hydrocarbons are highly branched, representing a high-octane number, while oxygenates mainly consist of series of alcohols and acids. The development of a production technology for direct conversion of methane and carbon dioxide to higher hydrocarbon and oxygenates using novel catalytic system will probably be more economically desired [39]. It is also important to note that carbon should not be used as a source of fuel but

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chemicals and materials and all non-carbon sources of energy such as solar, wind, geothermal, tidal, nuclear and above all hydrogen from water splitting will meet the requirements of the Paris Agreement [5].

7 Biomass Waste as Precursor for Chemicals and Materials Biomass is a renewable energy source having sufficient energy value per unit mass, but which is lower than that of fossil fuels. Hence, biomass must be valorized to produce biofuels (in solid, liquid and gas forms such as methane and hydrogen) for sustainable development, and green hydrogen from water splitting will play the most important role. Worldwide attention is focusing on the use of lignocellulosic biomasses for the sustainable production of biofuels and bio-derived chemicals. The key components of biomasses (cellulose, hemicellulose and lignin) have the potential for the sustainable production of several building block intermediates for modern bio-refineries. Cellulose and hemicellulose are mainly formed of C6- and C5-sugars, respectively, while lignin is mainly composed by phenolic units. Such a wealth of chemical functionalities represents, at present, the most promising alternative to petroleum resources. A variety of chemicals can be derived from lignocellulosic biomass, whether waste or purposely grown, the structures of cellulose, hemicellulose and lignin suggest several catalytic processes can be used to depolymerize and make fuels and chemicals (Figs. 9, 10 and 11). The importance of green hydrogen is clear since hydrogenation/ hydrogenolysis, dehyrogenation and oxidation are needed to make bio-based highly valuable chemicals [5]. Other important chemicals can be derived through condensation, hydrolysis, hydration, isomerization, dehydration, esterification, alkylation, dealkylation, oligomerization and demethoxylation [40, 41]. The 14 top platform chemicals derived from biomass are listed in Table 2. Many agricultural waste are being produced in all countries that could be converted into biofuels [42] using various treatment and production methods like thermochemical conversion (combustion, gasification, pyrolysis and hydrothermal liquefaction), biochemical conversion (anaerobic digestion, microbial fermentation and enzymatic hydrolysis) and chemical treatment (biodiesel production and transesterification). Pyrolysis of biomass produces hydrocarbon gases, liquid bio-oils and porous biochar. Biochar could be employed in farms to hold nutrients and water. Biochar can also be used as a green binder to bind urea together to make a fertilizer. Steam reforming of bioethanol will give blue hydrogen. Other biomass derived chemicals like methanol, butanol, ethylene glycol and glycerol (from biodiesel) are important sources of blue hydrogen. Hydrogen production from biomass is a promising bioenergy with carbon capture and storage which is a blue hydrogen that could produce low-carbon hydrogen and generate the carbon dioxide removal envisioned to be required to offset hard-to-abate emissions.

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Fig. 9 Basic structure of biomass as precursors of different chemicals which can be manipulated through catalytic processes such as hydrogenation/hydrogenolysis, dehydrogenation, oxidation, condensation, hydrolysis, hydration, isomerization, dehydration, esterification, alkylation, dealkylation, oligomerization and demethoxylation

Sustainable biomass feedstocks, namely agricultural residues and waste, will have negligible bearing on food security and biodiversity. The blue hydrogen manufacture from (waste) biomass or bio-derived alcohols represents a neglected near-term opportunity to generate CO2 removal and low-carbon hydrogen. Hydrogen can aid to decarbonize difficult-to-electrify areas, store energy from irregular renewable power and be implemented as a chemical feedstock. However, the grey hydrogen is made from fossil natural gas (methane) through steam reforming which responsible for about 2% of global GHG emissions. Hydrogen production from biomass generates a high purity stream of carbon dioxide well suited for CCUS. Bio-hydrogen is the only hydrogen production route that will lead to the net-negative CO2 emissions when coupled with CCUS.

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Fig. 10 Common C5 and C6 sugars found in hemicellulose which are precursors to a number of chemicals

Fig. 11 Lignin based valuable products

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Table 2 Most important platform chemicals derived from biomass [5, 37] BPM Fumaric acid

Structure

BPM (S,R,R)-Xylitol

Glycerol

3-Hydroxypropionic acid

L-Glutamic acid

3-Hydroxybutyrolactone

Itaconic acid

2,5-Furandicarboxylic acid

Glucaric acid

Sorbitol

l-Malic acid

Succinic acid

Levulinic acid

L-Aspartic

Structure

acid

Biomass feedstocks for bio-energy are often cultivated in countries like Brazil, India and others in South East Asia in large-scale monoculture plantations like sugarcane that have numerous socio-environmental bearings, including compromising food security, harming biodiversity, increasing competition for natural and agricultural land, manipulating food prices and aggravating water scarcity. With a rising demand for food production due to ever increasing population and unprecedented biodiversity loss, biomass feedstocks for blue hydrogen manufacture should have minimal influences on food production, biodiversity and the natural capital. Thus, purpose-grown bio-energy crops are becoming less appealing, and crop residues, household food waste and livestock manure are considered the most suitable for biogas production through anaerobic fermentation. These feedstocks do not necessitate purpose-grown bio-energy crops; their use does not compete with productive agricultural land and does not harm biodiversity through agricultural enlargement. In our seminal paper [5] on comparison of crude oil versus bio-refinery, we proved that it makes more environmental and economic sense in using bioethanol as a feedstock than as biofuel. One kg of crude oil gives 32 MJ of energy and 0.2 kg of chemicals, whereas 1 kg of biomass gives either 6 MJ energy or 0.8 kg of chemicals. So it is better to convert into chemicals than to refine. Indeed biomass should never

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Bioethanol

Ethylene

Polyethylene (60%)

Ethylene oxide (7%)

Ethylene glycol (7%)

Polyester

Styrene monomer (7%)

Polymers & rubbers

Ethylene dichloride (12%)

PVC

Others (7%)

Alpha-Olefins

PVA

Fig. 12 Biethanol to value-added industrial products. Carbon should not be used as a fuel to achieve the net zero goal in an effective and faster pace [6]

be used as a source of fuel but to make value-added chemicals and materials; for instance, bioethanol (Fig. 12). Both green and blue hydrogen can be utilized in hard-to-electrify segments, namely cement, steel, refining, ammonia and glass industries. Biomass needs to be separated into cellulose, hemicellulose and lignin fractions. Cellulose and hemicellulose are the sources for various platform chemicals like levulinic acid, 5-hydroxymethylfuran (HMF) and furfural. Lignin is a source of hydrocarbon compounds like olefins or aromatic derivatives, jet fuel and ethylene. The catalytic hydrogenation of (hemi) cellulose, hexose, furans, organic acid, lignin and other bio-derivatives will contribute to the income of agriculturists. Hydrogenation is an efficient method for selective synthesis of combustible fuels and high value-added chemicals. Cellulose can be converted into combustible gases by hydrogenation, and methane is one such gas among them. The sugars, hexoses and pentoses can be dehydrogenated into furfural and HMF which are important chemical platform intermediates for tetrahydrofurfuryl alcohol, levulinic acid and its esters, furfuryl alcohol, HMF, γ-valerolactone, etc. The conversion of lignin to benzene, toluene and xylene which are the major petrochemicals for chemical industry and produce 60% of all aromatic compounds is possible through hydrogenation/hydrogenolysis. Lignin depolymerization is required to produce platform chemicals, upgradation of bio-oils by hydrogenation and biochar. Polyols are definitely among the most appropriate substrates for the production of H2 or syngas that can be further used as building blocks for the manufacture of methanol and other chemicals, including liquid hydrocarbons through the Fischer–Tropsch synthesis. After cellulose and hemicellulose are broken by acid or reductive catalyzed hydrolysis, glucose and xylose can be straightforwardly hydrogenated into the corresponding C6 and C5 polyols, sorbitol and xylitol, respectively. C6–C2 polyols, including 1,4-butanediol (1,4-BDO), 1,2- and 1,3-propylene glycol (1,2-PDO and 1,3-PDO) and ethylene glycol (EG), are extensively used as ingredient or additives

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in food, pharmaceutical and cosmetic industry as well as cheap monomers for the manufacturing of polymers, coatings, adhesives, etc. Xylitol is the most widely used sweetener characterized by a lower calorie-content and reduced glycemic index (GI) with respect to sucrose. Sorbitol has been successfully used for over the years for making polyurethanes. Ethylene glycol is an antifreeze agent which is a main component in the production of bio-PET while other bio-based diols, besides their direct uses, are now used as co-monomers in bio-elastomeric polymers. New catalytic technologies require a cost-effective reduction of the oxygen content in bio-polyols permitting the production of H2 , fuels and other valuable chemicals. Glycerol is the co-product of biodiesel, typically 10% by weight, can be used to make more than two dozen chemicals. Unless glycerol is valorized, biodiesel production cannot compete with petro-diesel. Thus, farmers should recognize that there are marvelous opportunities to valorize agricultural waste using green and blue hydrogen to increase their income. Only the growth of grain or fruit production will not enhance their income, but making sensible use of all parts of plants and waste thrown or burnt as waste will be part of a circular economy.

8 Plastic Refining: Chemical Recycling Plastics refining is a GHG intensive process. Carbon dioxide emissions from ethylene production are projected to increase by ~34% over the period 2015–30. For instance, PVC is an extensively used thermoplastic due to its excellent properties such as stability, being cheap and workability. It is a multipurpose general plastic commonly used in construction, piping and many other consumer goods. PVC is highly polar and possesses a good insulation property, but it is inferior to other non-polar polymers like polypropylene (PP) and polyethylene (PE). PVC, PE and PP are usually used in piping, water sanity and medical industries, etc., whereas PP is extremely thermally resistant and it can withstand much higher temperatures than PVC. All these polymers including PET, nylon and PU contribute to carbon footprint and global warming. PVC is demonstrated to have higher energy consumption and CO2 gas emissions which that show its high potential in global warming than other plastics. Likewise, the recycling of PVC has shown substantial contributions in lowering the effect on climate change [43]. About 40% of plastics are used in packaging globally. Typically, packaging is meant for a single use (SUP), and therefore so there is a reckless turnaround for disposal at all places. SUPs are used in many applications such as tires, fabrics and coatings. Consumers need choices to avoid plastic waste such as legal means to encourage plastic collection through a refundable deposit scheme on SUPs, collection at regular intervals and avoiding plastic waste going as a mixture in municipal solid waste (MSW). The packaging can be dealt with in three different ways including landfill, incineration or recycling. Waste incineration leads to the largest climate impact of these three options. According to the As per the World Energy Council (WEC), based on the current trend in plastics production and incineration upsurge as

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anticipated, GHG will rise to 49 MMTA by 2030 and 91 MMTA by 2050. Landfilling has a much lesser impact on climate than incineration. But the landfill sites can be related with similar environmental issues. Recycling is a much better option. With regard to the little costs of virgin plastics, recycled plastics are high cost with low commercial value. It makes recycling lucrative only seldom, and so it calls for substantial subsidies by the government authorities. On the contrary the chemical recycling of polymers including depolymerization and hydrogenation are excellent choices. Plastic products are an integral part of modern civilization and can be categorized broadly into the following types [43]: Type 1: polyethylene terephthalate (PET) used in plastic beverage bottles. Type 2: high-density polyethylene (HDPE), used for milk pouches. Type 3: polyvinyl chloride (PVC), used pipes used in plumbing, vinyl tubing, and wire insulation. Type 4: low-density polyethylene (LDPE), used in plastic sheets or packaging. Type 5: polypropylene (PP), used in bottle caps, packaging and plastic furniture. Type 6: polystyrene (PS), used in styrofoam, beverage lids and straws. Type 7: other non-recyclable plastics and all thermoset plastics (acrylics, nylons, polycarbonates, acrylonitrile butadiene styrene, ABS and polylactic acid). Type 8: Polyurethanes (PUs): extremely versatile elastomer used in countless such as furniture, bedding and seating; thermal insulation; elastomers; footware; straps; coatings. According to the survey by the Ellen MacArthur Foundation survey [44] only ~2% of plastics are recycled through chemical conversions into products with the similar functionality. Around 8% are ‘downcycled’ to chemicals of lower quality, whereas the remaining is landfilled, goes into the environment or incinerated. Therefore, cutting down emissions associated with plastics would need the following approaches: reducing waste, retaining materials by restoring or remanufacturing and recycling. Chemical recycling encompasses three mechanisms by which the polymer is purified from plastics without changing its molecular structure, is depolymerized into the monomer building blocks, which in turn can be repolymerized [45]. It is converted into chemical building blocks that can thus be used to produce new polymers. Polymer upcycling such as SUP conversion into new products is all now worthy of practice. If government-established recycling targets are to be attained, the relationships between consumers, municipalities and petrochemical production must be enhanced. After all, public opinion is moved by media images of an endangered planet and eco system. Only through the collaboration of people, municipalities and industry—supported by improved technology along the recycled plastics supply chain, a solution for this global problem can be achieved. The concept of circular economy for plastics will require many innovative ideas since plastics offer significant benefits to global sustainability, predominantly in transportation, and there are no substitutes readily available for immediate disposition at global scales. Therefore, plastics will be an integral part of in our activities for the foreseeable future. Design of plastic products for circularity involves reuse, recycle and remanufacturing principles. SUP must be the exemption rather than the rule.

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The recycling of plastic is met with additional problems because different additives are used to enhance the performance, functionality and aging properties of the base polymer. Additives are functional additives (plasticizers, lubricants, slip agents, stabilizers, antistatic agents, flame retardants, curing agents, nucleators, biocides, foaming agents, catalyst deactivators, etc.), colorants (pigments), fillers (calcium carbonate, barium sulfate, mica, talc, kaolin and clay,) and reinforcements (carbon fibers and glass fibers,). Identification, separation and disposal of additives are a big hindrance to recycling into the virgin resin [43]. Mixed plastics can be incinerated for energy recovery, but it frequently creates carcinogenous pollutants. Therefore, only 12% of waste is incinerated in the USA, and incineration underestimates the potential that these polymers hold. Plastic gasification, pyrolysis and hydrothermal processing (HTP) are all thermolysis processes used to depolymerize plastics using heat. Pyrolysis of plastics into fuel oil is relatively mature technology. HTP takes place in an autoclave using water as a solvent, catalyst or reactant requiring moderate temperatures (280–450 °C) and pressures (70–300 bar). Supercritical water is used to liquefy polyolefins into oil or gas products (Fig. 13) [39, 40]. In solvolysis, xylene and toluene seem to be good solvents, whereas hexane and methanol work well as anti-solvents to recover the common polymers like HDPE, LDPE and PS in high yields. On the contrary, methylene chloride (MDC) and benzyl alcohol are good solvents to dissolve PVC and PET. Chemolysis is meant to initiate a reverse reaction of the condensation reactions and uses chemicals to depolymerize polymers which only works for condensation polymers like PET and PU. Condensation polymers are equilibrium materials, and hence, addition of condensation product like ethylene glycol and heat reverses the polymerization. Thus, chemolysis cannot depolymerize additive polymers like polyethylene (PE) and PP. Chemolysis reactions

Fig. 13 Opportunities abound for technological advancement in the field of chemical recycling; adopted from [43]

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include aminolysis, glycolysis and methanolysis. Selective solvent extraction (SSE) and chemolysis are good for sorted plastics and condensation polymers, respectively, which cannot be used to treat mixed plastic [43]. Similar to pyrolysis, HTP favors polyolefins, but it can handle higher quantities of non-polyolefins plastics, including PVC and PET. HTP is used to convert PP into PET, PP, PS and polycarbonate into fuels and naphtha [46, 47] and wax [48].

9 Hydrogenation of Plastic Waste to Valuable Fuels, Monomers and Chemicals Hydrocracking using metal catalysts over solid acid supports leads to cracking of heavy hydrocarbon molecules into lighter unsaturated hydrocarbons and the saturation of these newly formed hydrocarbons with hydrogen is a well-established refinery technology. It can be used for plastic waste. The advantages of hydrogenation over other methods including incinerations are conversion of waste plastic to high value products while simultaneously handling troublesome atoms (Cl, N, O and S) by hydrodechlorination (HDC), hydrodenitrogenation (HDN), hydrodesulfurization (HDS) and hydrodeoxygenation (HDO) in the hydrotreating processes. The technologies for absorption of HCl, NH3 , H2 O and H2 S are already well established. Dioxin neither survives the hydrogenation process nor does produce super toxic products. The metal impurities remain in present state during the process due to hydrodemetallation (HDM). A catalytic cascade process where hydropyrolysis was coupled with downstream vapor-phase hydrotreatment to upcycle mixed plastic waste into fuels. This tandem vapor-phase hydrotreatment technology is feedstock-agnostic and therefore capable of upcycling different kinds of personal protective equipment (PPE) waste [49]. Thus, hydratreating can be used as a favorable chemical upcycling technology for accomplishing a sustainable plastic circular economy.

10 Future Direction Many challenges exist in producing green hydrogen and to meet the so-called ‘111’ objective as well as using or reusing carbon dioxide in an economical manner. A foremost challenge encompasses determining how best to tap energy sources, since converting carbon dioxide into fuels and chemicals would require large energy input. Another task is to find new reaction routes, including novel heterogeneous chemical and enzyme catalysts, and design and operation of multiphase reactors where process intensification is achieved economically. Utilization of pure CO2 by different ways such as using plasma, photocatalytic system, electrochemical reduction and heterogeneous catalysis has been reported in

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the literature, most of which is on lab scale. However, scarce attempts have been made to develop continuous processes for converting carbon dioxide from flue gas to value-added products that are economical and have the potential to meet energy and material needs of the future on commercial scale. Over the next two decades, capturing CO2 from different sectors such as fossil fuel-based power plants, natural gas processing plants, bioethanol plants and cement plants could become an important method for mitigating climate change. Most of the captured CO2 would probably be injected deep into depleted wells and stored, which is known as carbon capture and storage (CCS). One proposed means of reducing the cost of CCS is to trade some of the CO2 for subsequent use. Thus, CO2 is now considered not just a pollutant but a valuable commodity which can be used to produce fuels, chemicals and materials. In the chemical industry, the greatest use of CO2 (~110–120 MMTA) is to produce urea. However, considering that global CO2 emissions are around 10 billion MTA, converting it to useful chemicals is not expected to make a big difference in the GHG emissions problem. However, researchers are making progress in developing efficient methods for converting CO2 into chemicals, so its potential use could be significant. Decarbonization of the transportation industry is needed most urgently. The new setting trend of the mode of transportation is electric cars and hydrogen-driven vehicles, but the question is still unresolved as most of the power plants are still using coal and petroleum as the primary source of energy which releases a huge amount of COX, SOX and NOX into the environment. However, the current refineries could use green hydrogen in their eight different processes needing catalytic hydrogenation which will reduce CO2 emissions from steam reforming of natural gas. It is predicted that by mid-2050s we may not have a viable means of extracting oil from the mother earth using current technologies. These problems along with GHG emissions, commitment to the Paris Agreement of 2015, aiming at net zero carbon by 2050, and containing global temperature rise to below 1.5 °C, have all propelled the development of a new clean energy alternative, which has to be renewable and can be utilized in the industry without any major modification of present infrastructure. For any alternate source, building new infrastructure in a short period and that too economically will be horrific. The three main characteristics of the energy supply chain which are essential for any type of energy infrastructure are the energy generation, storage and distribution and utilization. There are a very few options available which can fulfill all the these criteria.

11 Conclusions Net (carbon) zero is a grand plan to restrict the global temperature rise to less than 1.5 °C whereby CO2 emissions must be reduced from ~40 Gt today to less than 10 Gigatons by using non-carbon renewable energy sources. Green hydrogen will play a massive role in transforming C1 off gases like CO2 into valuable chemicals and materials. By 2050, almost 49,000 TWh of energy will be required among which 73%

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will be from renewable resources in which solar energy, wind energy and hydrogen will contribute significantly along with hydro and nuclear. Both blue and green hydrogen will contribute about 24% in the renewables totaling to about 539 MMTA. Hydrogen production will be cheaper than the grey hydrogen cost by then. The CO2 conversion into gaseous or liquid hydrocarbons needs reaction conditions of high temperature (250–450 °C) and high pressure (20–40 bar), but the conversion is low due to difficulty in the activation of CO2 . Therefore, currently available technologies are not economically suitable for industrial implementation. Efficient heterogeneous catalysts can reduce the energy needed for reactions by reducing the activation energy. Various catalysts need to be actively investigated to enhance CO2 conversion and to control selectivity toward the specific desired products. In fact, hydrogen will play an important role in all these chemicals. Hydrogen is regarded as energy carrier, and it is only be produced by using energy from other source. Sustainable methanol economy refers to the combination of captured CO2 from various waste sources and cheap hydrogen by using renewable energy to produce methanol. It is also referred to as ‘liquid sunshine’ and has a great potential to resolve the energy crises and mitigate climate change. Throughout the last few decades, there is an advanced and viable development of technologies in catalytic hydrogenation of CO2 for methanol synthesis, leading to a carbon–neutral energy sources by scavenging massive CO2 released into the environment from various industries. Most of the hydrogen is produced from hydrocarbon processing in the petrochemical industry, usually by gasification of coal or natural gas reform, which typically costs around at < 2 USD/kg. The cost of hydrogen production mainly comes from the energy (heat and electricity) consumed during the process. Renewable energy is the cheapest option for hydrogen production, including geothermal, wind, hydropower and solar energy. Therefore, the best approach to consider is to produce hydrogen by renewable energy, preferably solar or wind and use that hydrogen for CO2 hydrogenation to methanol, DME and ammonia synthesis. For sustainable hydrogen production for ammonia synthesis, water electrolysis using wind and solar power is used, which provides a clue for methanol synthesis. In the future, thermochemical water splitting cycles such as Cu–Cl could compete for cheap production of green hydrogen if they are coupled with solar energy as proved in the Institute of Chemical Technology-ONGC Energy Centre (ICT-OEC) hydrogen production technology. DME is viewed as a ‘2G fuel/biofuel’ and is a powerful, empowering fuel that can range from being ultra-low carbon to carbon-negative. It can significantly reduce the carbon footprint of the transportation sector and beyond (a) as an energy-dense, cost-effective means to move toward renewable hydrogen, (b) as a blending agent for propane, and (c) as a diesel replacement. DME can also be a clean fuel produced from emitted CO2 captured from flue gases or directly from power plants. Carbon dioxide refineries are not far away to be seen and to be believed. Thus, hydrogen can substitute fossil fuels in some carbon intensive industrial processes, such as steel, chemical and allied industries. It can present solutions for difficult to abate parts of the transport system, in addition to what can be accomplished through electrification and other renewable and low-carbon fuels. Net zero should happen much before 2050 during the lifetime of many readers. Biomass including waste and

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plastic waste will be major sources of chemicals and materials where hydrogenation/ hydrogenolysis and oxidation will lead too protection of environment, provision of fuels, materials and energy. Although bioethanol and other biomass derived chemicals can be used to make blue H2 , it should not be burnt as a fuel if we want to achieve the net zero goal before 2050. Carbon should be used as a source of chemicals and materials. Bioethanol is more valuable as a feedstock for bio-refinery than a fuel as our analysis showed [6]. It makes more economic sense in addition to the net zero target. Chemical recycling of waste plastics will have great benefit. Huge quantities of plastic waste can be converted into fuels and chemicals, and hydrogenation will play a significant role in treating all sorts of polymers and their mixtures. Circular economy must be made mandatory in all sectors and future societies should be taught that material recycling through physical, chemical and biological means, and use of green energy will save us from climate change and GHG emissions. Hydrogen will be a true savior in these sectors.

References 1. The Intergovernmental Panel on Climate Change (IPCC). https://www.ipcc.ch/ 2. The Paris Agreement 2015. https://www.un.org/en/climatechange/paris-agreement 3. COP26 achievements at a glance. https://ukcop26.org/wp-content/uploads/2021/11/COP26Presidency-Outcomes-The-Climate-Pact.pdf. 4. https://www.climate.gov/news-features/understanding-climate/climate-changeatmosphericcarbon-dioxide 5. Yadav VG, Yadav GD, Patankar SC (2020) The production of fuels and chemicals in the new world: critical analysis of the choice between crude oil and biomass vis-à-vis sustainability and the environment. Clean Tech Environ. Policy 22:1757–1774 6. https://www.indianchemicalnews.com/opinion/carbon-dioxide-refineries-of-future-and-netzero-goal-prof-ganpati-d-yadav-emeritus-professor-of-eminence-and-former-vice-chance llor-ict-mumbai-14261 7. https://www.millenniumpost.in/business/the-case-for-hydrogen-economy-431824 8. https://ceenergynews.com/hydrogen/can-green-ammonia-overtake-green-hydrogen-in-theenergy-transition/ 9. https://energy.economictimes.indiatimes.com/news/renewable/opinion-climate-change-hyd rogen-economy-and-net-zero-emissions/89671296 10. Yadav GD (2023) In pursuit of the net zero goal and sustainability: hydrogen economy, carbon dioxide refineries, and valorization of biomass & waste plastic. AsiaChem (3):110–123 11. BP Energy Outlook, 2022, https://www.bp.com/en/global/corporate/energy-economics/ene rgy-outlook.html 12. Yadav GD (2021) The case for hydrogen economy. Curr Sci 120:971–972 13. Hydrogen Council. https://hydrogencouncil.com/en/ 14. Hydrogen Roadmap Europe: A sustainable pathway for the European Energy Transition (2019). https://www.clean-hydrogen.europa.eu/media/publications/hydrogen-roadmapeurope-sustainable-pathway-european-energy-transition/en 15. International Energy Agency (IEA). https://www.iea.org/ 16. Bloomberg New Energy Fund (BNEF). https://about.bnef.com/ 17. US Department of Energy. https://www.energy.gov/eere/fuelcells/hydrogen-production

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Managing Energy Transition and Challenges of New Energy Gautam Sen

Abstract Global warming and its devastating effects on the climate have awakened the world to the reality that using fossil fuels as a source of energy is not sustainable. Natural processes of hydrocarbon generation and accumulation, which take millions of years, cannot be undone in decades without paying a heavy price. Renewables and hydrogen could be the alternative to fossil fuel, but the transition process can only be bumpy, for it is only in the recent past that this change is being initiated. This paper gives a perspective on the state of development of the alternate sources of energy including investments, the technological and policy challenges. Decarbonisation methods, essential to keep carbon dioxide levels in the atmosphere within limits, in the intermittent period have also been discussed. Geopolitics and economics have played a significant role in ensuring supply of fossil fuel during the last few decades, which resulted in the economic development of the Middle East. All this is also likely to change and countries, which have a rich endowment of rare earth metals, essential for production of alternate energy and their processing facilities, will reap the benefits. Monopoly in the resources required for development of alternate energy can create issues of energy security and this needs to be checked for a sustainable global development. Absence of cheap fossil fuel energy can enhance development cost which the non-OECD (organisation for economic cooperation and development) countries will have to bear, besides devastations due to global warming. Whether OECD countries will compensate poorer countries against this devastation is anyone’s guess. Managing a smooth transition from fossil fuel to hydrogen and renewables before irreversible climate change occurs is the challenge mankind is facing today. Human beings, today are confronted with two alternatives i.e. to transform energy sector to renewable based or perish. Learning objectives: • Need for energy transition to reach Net zero • Decarbonisation methods in the energy sector G. Sen (B) Former Executive Director, Oil and Natural Gas Corporation, Senior Vice President RIL (E and P), C-498 Defence Colony, New Delhi 110024, India e-mail: [email protected]

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Goel and G. Sen (eds.), Climate Action and Hydrogen Economy, Green Energy and Technology, https://doi.org/10.1007/978-981-99-6237-2_5

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• Hydrogen production and feasible options of storing hydrogen • Challenges in using hydrogen as a fuel and managing energy transition Keywords Greenhouse gas · Adsorption · Absorption · Net zero carbon · Physisorption · Chemisorption

Abbreviations CCS DRC FCEV IMF MOFs OECD

Carbon Capture and Storage Democratic Republic of Congo Fuel Cell Electric Vehicle International Monetary Fund Metal–Organic Frameworks Organisation for Economic Cooperation and Development

1 Introduction Renewables are the only path to real energy security, stable power prices and sustainable employment opportunities. — Secretary General of the United Nations [1]

There is a famous video clip made by the American film director Steven Spielberg and produced by the United Nations in 2021 [2], wherein a Dinosaur cautions human beings against a possible extinction, as a climate disaster is looming. A recent World Bank report [3] has also stated that parts of India will soon experience heat waves beyond the limits of human survival. Burning of fossil fuels, since the mid-eighteenth century, has caused an enormous rise in greenhouse gas emissions. Carbon dioxide and Methane are the chief sources of greenhouse gas. Methane molecules dissipate over time and therefore are relatively less harmful, while carbon dioxide is stable and its effects are cumulative over time. Carbon dioxide levels in the atmosphere have gone up from 280 parts per million at the beginning of the industrial era to over 425 parts per million today. Global temperatures have already crossed 1 degree and with today s rate of global emissions of carbon dioxide, (37 giga tonnes per annum); global temperatures are bound to cross 1.5°. Mathematical models have predicted that unless aggressive methods are adopted to reduce carbon emissions in the atmosphere, global temperatures could increase as much as 2.2° above pre industrial levels by the end of the century [4]. Higher global temperatures can melt glaciers deposited at and near the poles, as well as within different mountain ranges, causing a sea level rise and making presentday coastal areas, out-of-bounds for habitation. In addition, a large part of tropical

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areas could be subjected to extremes of weather variation like intense heat, forest fires, tornadoes, cyclones, very high rains, floods and desertification, causing shortage of agricultural products. Floods in Pakistan, the United States and the unusual summer in Europe are recent testimony to the fact that climate change is real and is happening. According to the World Meteorology Report [5] published in 2021, weather, climate and water hazards accounted for 50% of all disasters and 45% of all reported deaths causing 74% of reported economic losses, from 1970 to 2019. More than 91% of these deaths have occurred in developing countries, as defined by the United Nations classification. It is abundantly clear, that for sustenance of life on Earth, further emissions of carbon dioxide and other greenhouse gases have to be stopped. However, alternate energy industry is still in infancy. Zero carbon emissions therefore cannot be achieved before the end of this century in the most likely scenario. It is therefore decided that each country will cut down their emission and also use carbon capture and storage methods to reduce Net zero carbon emissions. The 2022 United Nations Climate Change conference referred to as the COP 27, held from 6 to 20 November 2022, in Egypt has recognised the necessity of creating a “Loss and Damage” fund for the poorer nations who are likely to suffer a permanent erosion of their land and infrastructure. However, details are still to be finalised. Developing nations maintain that developed nations have used cheap fossil fuel like coal, gas and oil in order to improve the quality of life of their people while circumstances today are such that this luxury of cheap fuels are not available for them without creating a havoc in global climate. As a result, rich countries had pledged 100 billion US dollars, but only a fraction has been so far paid. It is therefore anyone’s guess whether such a “Loss and Damage” corpus will be created and money disbursed. Developing and poorer nations are finding it difficult to address the dual challenge of the need to improve the wellbeing of their citizens, which invariably needs investments on infrastructure, on one hand and on the other the necessity to curb carbon emissions. Resources and technology required to switch to alternate energy, at least partially, and maximise energy intensity while creating new infrastructure is often not available with them. In addition, some of these countries will be exposed to extremes of weather which will make their situation still more difficult.

2 World Energy Outlook Report 2022 Key Points Russia’s invasion of Ukraine has turned an economic recovery from the pandemic, into a full-blown energy crisis with disruptions in supply chain of oil and gas. Oil prices have been volatile, fluctuating between USD 100 per barrel in mid-2022 before falling back to around USD 70, with threat of recession. Gas and coal prices also went up in this period leading to an upward pressure on electricity costs globally and increasing food insecurity in many developing economies. There is a growing

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realisation that energy security is essential and changing geopolitics can jeopardise the entire economy by supply chain disruptions. World Energy Outlook report 2022 [6] has deliberated on the geopolitical effects on energy supply. The main takeaways of the report are as follows; European countries are striving to move away from fossil fuel to nuclear and renewables with the disruption in supply of Russian oil and gas. However, these countries had to fall back on coal for immediate fuel requirements. Global investment per annum in green energy is set to go up to 2 trillion US dollars by 2030, which is double of today’s investment, and further to 4 trillion US dollars by 2050. The major contributors are Europe’s spurt in investment in renewables, China’s massive clean energy built, Korea’s thrust on nuclear and green energy and India’s domestic renewable target of 500 GW. However, in the transition period, the report has acknowledged that investment in finding and extracting fossil fuel needs to continue. There will be a reduction in Russian clout in the supply of oil and gas. Though China and India have stepped up the import of Russian oil, yet, there could be as much as 1 trillion US dollar loss to Russia in fossil fuel export by 2030, and it is very unlikely that Russian exports of fossil fuel will be close to the 2021 numbers. Targets for Global carbon emissions peak now have been preponed to 2025 from 2030. Europe will face long winters, probably a more severe winter in 2023–24, which could even be a strain on European Union solidarity. Even if all the investment related pledges are met, including reduction of global carbon dioxide emission to 23 Gt by 2030, yet, it is very unlikely that global temperatures will not exceed 1.5° by 2030.

3 Challenges to Reach Net Zero Governments across the world have to ensure that the supply of energy is secured affordable and is sustainable. This has become a major challenge. 35% of the World’s population lives in China and India, and both are poised for economic growth and consequently, energy demand will be high. They may, therefore, find it difficult to be a Net zero carbon emission country by 2060 and 2070 as they have promised. In order to meet their shortfalls, OECD countries may have to become net carbon neutral by 2040 or earlier. Will this be possible? Sub Saharan Africa may not reach carbon neutrality even by the turn of the century. Total contribution of renewables, today, globally, in the world’s energy basket is shown graphically below, adapted from British Petroleum s Statistical Report 2022 [7]. This report is based on 2021 data and does not incorporate changes due to the Russian invasion. The dip in the year 2020 is due to the effects of lockdown during COVID-19 pandemic. As per this report, while consumption of coal and oil has decreased, the increase in energy demand is being met by increase in renewables mainly solar and wind, and today share of renewables in energy basket is around 20%. It is still a while before we are past the age of fossil fuels and a quantum jump

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in production of alternate energy in order to replace fossil fuel is the biggest challenge facing mankind. At the same time, it is important to ensure that energy from fossil fuel is available during the entire transition period to make up for the shortfalls.

Source BP Statistical review of World energy 2022

4 Decarbonisation Fossil fuel will continue to be in use during this entire transition period. In order to attain a Net zero emission, therefore, it is essential to capture carbon dioxide from the atmosphere and store it underground. Carbon dioxide can be captured at the source of generation at power plants, and in industries like cement, iron and steel where carbon dioxide emissions are high. Agriculture, land use and forestry also contribute to a significant amount of carbon dioxide emissions Power plants which are based on post combustion of fossil fuels, can be retrofitted with machines to capture carbon dioxide without any major alteration. Absorbents like liquid hydroxides of potassium and sodium or amine-based solvents have great affinity for carbon dioxide and capture carbon dioxide when air is passed through it. Carbonates formed need to be heated to very high degree to regenerate concentrated carbon dioxide. Adsorbents, in contrast, are solid solvents and use physisorption and chemisorption to adsorb carbon dioxide. Metal organic framework increases the area of contact between the solid adsorbent and air. The solid adsorbent reacts chemically with the adsorbate and new bonds are formed, which when heated and in low pressure, release a gaseous stream of carbon dioxide. Adding ecologically inert biocarbon to the soil and living biomes can act as biological scrubber for capturing carbon dioxide, especially in areas where

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agricultural activities emit carbon dioxide. Soil acts as carbon sink. Bio sequestration also can directly capture carbon dioxide from ambient air. Carbon dioxide can also be captured and stored in sea beds using planktons. The total amount of carbon in the oceans is around 50 times that in the atmosphere. Plankton produces organic carbon through photosynthesis, within the euphotic zone. Some of the carbon is consumed by sea life and the remaining is broken down chemically and carried to deep waters as the living organisms die. Methods to enhance growth of phytoplankton can enhance the rate of carbon capture. Direct air capture methods from ambient air can also reduce the effects of carbon dioxide emitted by vehicles in cities but are expensive. An interesting consequence of sea ice melting in the polar regions is that natural absorption of carbon dioxide by oceans increases. This, may not undo the damage caused by glaciers and sea ice melting, which in turn reduces the reflectivity of solar rays, thereby heating the planet more. Carbon dioxide is usually stored in old oil and gas fields, within coal seams, in saline aquifers and the recent trend is to store them within basalts where they solidify as carbonates and there is no necessity of monitoring of leakage back to the atmosphere. Iceland is one such area where it is being experimented. If successful then India could adopt this technique and store carbon dioxide within Deccan traps and Raajmahal traps and the two together cover a large part of Indian subsurface. Technology for carbon capture and storage is by and large known; [8] the issue is financing of large-scale projects worldwide. Unless there are major policy changes like implementation of carbon tax as well as incentives for carbon capture and developing a fullfledged carbon market which can generate financial resources, decarbonisation will not become a commercial activity. This is however not to say that mankind has the last word on carbon capture and storage. Further research to reduce costs and designing new methods to capture and store carbon will help in making this a commercial success. Captured carbon dioxide can also be reused in enhancing oil recovery in old fields as well as in aerated soft drink industry and in food and drug industry. The more the delay in implementation of carbon capture and storage in a concerted manner, more will be the carbon accumulation in the atmosphere and greater will be the economic losses due to climate disasters. Can inter-governmental bodies like International Energy Association or United Nations enforce carbon capture and storage across the world or at least in the major polluting countries? That is the big question.

5 Solar and Wind Energy The Paris Agreement is a legally binding international treaty on climate change adopted by 196 countries at COP21 in December 2015, to limit global warming to well below 2° and preferably to 1.5° above pre industrialisation level. It set the ball rolling for the gradual phasing out of fossil fuels and their replacement with renewables. It was decided to fix targets for peak global carbon emission by 2030, which has now been preponed to 2025, and to reach carbon neutrality by 2050.

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Whether this will be feasible or not is another matter but at least there is a greater urgency for switching to renewables as soon as possible. There has been a quantum jump in global renewable power capacity from 800 GW in 2004 to around 3000 GW in 2022. China led the global transition to renewable energy during this period, accounting for around 40% of its total installed power capacity, while India possessed around 160 GW of power by November 2022. Yet, achieving a Net zero carbon world is a tall order, as it entails renewables contributing around 88% of the global electricity generation and 61% of global transportation as per International Energy Agency, estimates [9]. Solar energy is used for solar water heaters and house heating. The heat from solar panels enables production of chemicals, food, textiles and warm greenhouses, swimming pools and livestock buildings. Wind energy, similarly, can be used for milling grain and pumping water. Both Solar and wind energy can be converted into electrical energy and can be connected to the electrical grid system. Both can also be stored in Lithium and Sodium ion batteries which can power electric vehicles. They have proved to be more energy efficient and are cheaper as compared to hydrogen fuel cell (FCV). Eight per cent of the energy is lost before the electricity is stored in the vehicle’s batteries and another 18% is lost in driving the electric motor. Depending on the model, the battery-powered e-car thus achieves an efficiency of between 70 and 80%. However, only light vehicles can be driven by electrical battery and it also needs long charging time. Yet, electrical vehicles driven by solar batteries are suitable for city transport. Solar and wind energy powered battery driven vehicles cannot meet the energy requirement for heavy vehicles, for ships, aircrafts, etc. and therefore have a limited usage in transport and other heavy industry. The good news, however, is the rapid decrease in the cost of solar and wind energy with increasing research, and today, the cost of renewables is at par with fossil fuels and thus one component of energy trilemma i.e. affordability is met. China controls about 70% of the world’s lithium production, most of the world’s lithium-processing facilities and dominates lithium-ion battery production, producing around 73% of the 316 gigawatt-hours of global lithium cell manufacturing capacity [10]. Cobalt is found in Democratic Republic of Congo (DRC), Russia, Australia, Canada, Cuba, the Philippines, Madagascar, Papua New Guinea and Zambia with DRC, accounting for roughly 58% of global production and possessing 50% of the known global reserves of cobalt. Graphite are the dominant active anode material and Cobalt acts as the Cathode in lithium-ion batteries. China, India, Brazil, Canada, Mozambique, Russia, Ukraine, Pakistan and Norway remain the highest producers of graphite globally. China accounted for 65% of world graphite mining in 2018, and 35% of the total global consumption. Rare earth minerals like indium, dysprosium, praseodymium, neodymium and terbium are used in manufacture of solar panels and wind turbines. The global deposit reserves of these minerals are estimated at 120 MT, with the United States and China possessing a large share of them. China possesses around 85% of the global processing capacity for rare earth minerals. The monopolisation of the production and supply chains of the critical minerals is integral to China’s energy security strategy.

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Disruption to production chains originating from China can lead to a situation that puts in jeopardy the manufacturing of solar photovoltaics, batteries and electric vehicles around the world, thus seriously challenging the global energy transition efforts. The ongoing geopolitical competition between the United States and China could only add to the concerns of energy security. A sustainable development warrants reduction in consumerism. Reusing, recycling and reimaging waste products from both solar and wind farms is essential. China, India and the United States have already become dumping grounds for dead gadgets and further dumping will only be disastrous ecologically. Over 300 new mines for Graphite, Lithium, Cobalt and Nickel will be required to meet the demand of electric vehicle by 2035 [10] and there is no definite answer to, whether such a major increase in mining requirement can be met. Sustainability in using renewables can only be attained through scientific innovations with higher energy efficiency and major policy changes to provide incentives for recycled materials. Scramble for resources can also lead to deforestation, ecological imbalances, corruption and human right violation.

6 Hydrogen as a Fuel for the Future Hydrogen is fast emerging as the energy for future. Hydrogen burnt with air produces water and energy. Thus, hydrogen does not emit any greenhouse gases if it is ensured that it is produced with minimal carbon footprints. Hydrogen is not an efficient fuel and a hydrogen fuel cell requires 2–3 times more energy to drive the same distance as a battery-powered vehicle, as the overall Well-to-Wheel efficiency is only from 25 to 35%. However, hydrogen is suitable for the entire transport industry and can drive all kinds of vehicles, trains, ships and aeroplanes. The various industrial applications where hydrogen can be used are summarised below [11].

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Source International renewable energy agency Priority areas where hydrogen can be more effectively used are shown below [12].

Source International renewable energy agency

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It covers the entire gamut of applications where fossil fuels are being currently used, namely in industry, in transport, in power generation as well as heating, and this is why hydrogen is hailed as the future fuel.

7 Hydrogen Production Various methods for production of hydrogen [13] are shown below in a tabular form. Methodology and the source required to generate hydrocarbon decide the colour of hydrogen. The various methods are tabulated below.

Grey hydrogen is generated from natural gas, or methane, through “steam reforming”, which produces Syngas, a mixture of hydrogen and carbon monoxide. Carbon monoxide and steam further react to generate more hydrogen and some carbon dioxide. Blue hydrogen is also generated by steam reforming as above, and CO2 generated is captured and stored underground through carbon capture and storage (CSS). The entire carbon dioxide generated can however never be fully captured. Green hydrogen is the cleanest hydrogen and is produced by electrolysis of water using renewable energy sources, to generate electricity required for electrolysis. Three types of electrolysers are commonly used. Polymer electrolyte membrane electrolyser: The electrolyte is a solid plastic material. Water reacts at the anode to form oxygen and hydrogen ion. The ions move across the membrane to the cathode and combine with electrons which flow through an external circuit to form hydrogen. Alkaline electrolyser: Hydroxide ions are generated by electrolysis of liquid alkaline solutions and move toward the anode which in turn generates hydrogen on the cathode. Solid oxide electrolyser: It uses a solid ceramic material as the electrolyte that conducts negatively charged oxygen ions at elevated temperature of 700 to 800°. Steam at the cathode combines with electrons from external circuit to form hydrogen

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gas and oxygen ions. Oxygen ions move toward the anode, release electrons and form oxygen. Green hydrogen production is still within the realm of research with the thrust on reduction of high cost. In order to reach Net zero carbon, annual green hydrogen production has to be around 500 million Tonnes, roughly around 22% of total energy demand, by 2050, as per different estimates [12].

Source International renewable energy agency

8 Hydrogen Storage The energy per unit mass of hydrogen is substantially greater than most other fuels; however, its energy by volume is much less than liquid fuels like gasoline. A fuel cell driven electric vehicle needs about 5 kg of hydrogen for a 50 km drive and this will occupy a storage system of about 200 L, even at 700 bar (~10,000 psi), which is three to four times the volume of gasoline tanks, typically found in cars. A key challenge, therefore, is to store sufficient quantities of hydrogen onboard without sacrificing passenger and cargo space. This is why most of the research on hydrogen storage is focused on developing cost-effective technologies, especially in solid state, using materials-based storage technologies rather than on gaseous state which needs high pressure or liquid state which needs low temperature. Storage tanks using materialbased storage can store hydrogen at higher volumetric densities and then compress and liquefy hydrogen at ambient temperatures and pressure, using processes known as Physisorption and Chemisorption. Safety risks associated with storing hydrogen at high pressures are also reduced. During Physisorption, hydrogen molecules are adsorbed in the pores of metallic organic framework or in pores of activated carbon through Van der Walls molecular attraction and can be released with slight heating. It

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Table 1 Comparison of physisorption and chemisorption for hydrogen storage Physisorption

Chemisorptions

It is due to the formation of van der Waals forces

It is due to the formation of chemical bonds

It is reversible in nature

It is irreversible in nature

Physisorption is not specific in nature

It is very specific in nature

It has low adsorption enthalpy nearly 20 to 40 kJ/mol

Chemisorption has high adsorption enthalpy nearly to 240 kJ/ mol

It favours low temperature

It favours high temperature

Physisorption decreases with increase in temperature

Chemisorption increases with increase in temperature

It results in a multimolecular layer

It results in an unimolecular layer

Activation energy is less in physisorption

Activation energy is high in chemisorption

Source compiled by author

is still not a very efficient method of storage. During Chemisorption, atomic hydrogen binds with other elements to form compounds or solid solutions through a chemical reaction. Hydrogen can later be released through heating at a high temperature. A comparison of the two processes is tabulated Table 1.

9 Physisorption Hydrogen sorbents are micro-porous solids (e.g. activated carbons or metal–organic frameworks (MOFs)) with high surface area, where the hydrogen molecule adsorbs onto the surface through Van der Waals interactions. Hydrogen is thus stored with high gravimetric and volumetric hydrogen density at significantly lower pressures. Storage materials also need to be capable of fast charge/discharge rates within the temperature and pressure ranges of fuel cell operation and should sustain charge/ discharge cycles to last the lifetime of the fuel cell electric vehicle (FCEV). Physisorption on super activated carbon with slit-like micro-pores (raising ambition, 2022 2. United Nations Development Programme, Do not choose extinction, a Spielberg Video, Oct 2021 3. World Bank Report, Climate investment opportunities in India s cooling sector, Dec 2021 4. United Nations Environmental Programme, Emission gap report, Oct 2022 5. World Meteorological Report, State of global climate, 2021 6. World Energy Outlook report, 2022 7. British Petroleum s Statistical Report, 2022 8. Sen G (2021) Research and development pathways in direct air capture, climate change and green chemistry of CO2 sequestration, pp 181–194, Malti Goel et all edited, Springer Publication 9. International Renewable Energy Agency Report, Net zero by 2050-A roadmap for the Global Energy Sector, March 2021 10. Tagotra N (2022) The geopolitics of renewable energy. Nat Bureau Asian Res 11. International Renewable Energy Agency Report, Green hydrogen policies and technology costs, MAKING THE BREAKTHROUGH, 2021 12. International Renewable Energy Agency Report, Geopolitics of energy transformation, the hydrogen Factor, 2022 13. Dincer I, Acar C (2015) Review and evaluation of hydrogen production methods for better sustainability. Int J Hydrogen Energy 40:11094–11111 14. Sakintunaa B, Lamari-Darkrimb F, Hirscherc M (2007) Metal hydride materials for solid hydrogen storage: a review. Int J Hydrogen Energy 32:1121–1140 15. International Renewable Energy Agency Report, World energy transition outlook report; 1.5 deg pathway 2022

STI Policy Push Towards Hydrogen Economy in India Vandana Maurya, Paramita Ghosh, and Anshuman Gunawat

Abstract From the year 2019 to 2021, solar power generation increased by 47%, wind by 31% worldwide and it is interesting to note that to meet the growing demands of power and limit to 1.5° warming, the share of renewable energy of the world needs to be increased to 75% by 2030. Although COP 27 has outlined that limiting the warming to 1.5° would be difficult if countries keep shifting their targets. For India, transition to Net zero emission future may require an investment of $3 trillion over three decades and we need to phase down the usage of coal and revamp the use of renewable energy production along with hydrogen production. Green hydrogen will prove to be a milestone to achieve Net zero targets. This chapter gives a review of the energy transition in India and highlights the need of Science, Technology and Innovation Policies that provide a push towards turning India into a hydrogen economy. Lastly, the chapter emphasizes the need for financing and improved technology for increasing hydrogen with a major emphasis on green hydrogen. The Hydrogen Energy transition in India is a long process that needs technology, R&D, funding and policy support from the government, private players and academia alike. Learning objectives • Review of energy transition in India • Hydrogen energy leading the transition • Policy pathways to accelerate transition towards green hydrogen in India Keywords Hydrogen energy · Net zero · Energy transition · STI policies · Sustainable finance

V. Maurya (B) · P. Ghosh · A. Gunawat Motilal Nehru College, University of Delhi, New Delhi 110021, India e-mail: [email protected]

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Goel and G. Sen (eds.), Climate Action and Hydrogen Economy, Green Energy and Technology, https://doi.org/10.1007/978-981-99-6237-2_6

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Abbreviations ECB IPCC IEA ISTC NGFS PPAC RBI STI TPS TFSF TOE UNFCCC

External Commercial Borrowing Intergovernmental Panel on Climate Change International Energy Agency Inter-State Transmission Charge Network for Greening the Financial System Petroleum Planning and Analysis Cell Reserve Bank of India Science, Technology and Innovation Technology Policy Statement Task Force on Sustainable Finance Tons of Oil Equivalent United Nations Framework Convention for Climate Change

1 Introduction Various economies have reached the zenith of success and power due to availability, accessibility and affordability of various energy sources which fueled their development process as the energy use allows natural resources to be socially configured and allocated in a way that enhances and limits the growth evolution [23]. Energy has undisputed authority over the humans and societies. It has shaped the world in its present form [16] in his book “Energy and Society” delves into intricacies of relationships of energy use and evolution of human societies. He recognizes “energy as the part of cost of achieving all values” [15] in his book “The Energy Question” sees human activities as energy consuming processes which are dependent on undisrupted availability of energy from different sources [29] identified energy as the foundation of evolution of societies and base of all social change and progress. The Hydrogen energy can be used as high energy efficiency fuel, which could be a zero carbon fuel burnt with oxygen. Hydrogen usage varies according to output required. It can be used as chemical feedstock in various industrial processes, fuel cell for electricity generation or can be used directly through direct combustion. The main uses of hydrogen produced by industries are oil refining, ammonia production, methanol production, and steel Production via direct reduction of iron ore. Need for sustainability drives the transitions from the present fossil fuel-based economy to a renewable and sustainable circular economy, which could be the highly efficient engineering and the energy technological choices of the twenty-first century. This chapter is an attempt to review the role of policies in transitioning towards hydrogen economy. It explains the interlinkage of policies and growth of hydrogen energy using co-evolution framework. It also provides recommendations for smoothening the transition. In the circles of Science, Technology and policies scholars, it is well discussed and put forward that policy intervention can result in diffusion of technology. They emphasize that large number of actors, networks and institutions within

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Fig. 1 Historical perspective of world energy transition1

a socio-technical system can result in successful development, diffusion and use of technology [11]. This transition towards cleaner and decarbonized economies will require dedicated research and innovations along with positive policy push.

2 Energy Transition: Historical Perspective Our society has evolved from pre-industrialized low energy consuming society to high energy consuming society. Globally, energy demand is estimated to increase by over one-third till 2035, and power sector related CO2 emissions are expected to rise from an estimated 13 GT in 2011 to 15.2 GT in 2035 [32]. Looking at the history gives us a glimpse of energy transition that world has witnessed from coal to hydro to renewable energy. It is interesting to note that towards the end of the nineteenth century, electricity was discovered. The first power plants for electricity generation used steam engines which were replaced by steam turbines in 1884 and then finally to coal (Fig. 1). As coal started to gain dominance in every sector, oil was also used at that time but usually for illumination only. Whale oil was the finest quality source for illumination during the nineteenth century. Oil was preferred over coal due to its easiness for transportation, high energy density and well adaptability. As combustion engine was developed in 1876, steam engine was considered inferior and uneconomic. By the late nineteenth century, oil’s main market i.e., illumination was affected by development of electric bulb.2 In the twentieth century, coal share of primary energy supply increased to 50%. During this time, oil and natural gas consumption also started to 1

Retrieved from https://www.e-education.psu.edu/eme803/node/502 on 4th July 2022. The bulb, an invention of Thomas Alva Edison, revolutionized the illumination. It would have been a moment of miracle when first bulb was lighted.

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gear up. In 1908, Henry Ford introduced the first model-T automobile which used internal combustion engine. In the same year, Persia (later Iran) found oil. This changed the landscape of automobile ownership and personal mobility landscape of world. The automobile was fueled by gasoline which became a highly precious product. Car ownership increased and strengthened the oil’s place in energy mix. In 1938, oil was discovered in Saudi Arabia and Kuwait and it again changed the geo-political environment of the world. During this time, Hydro-power also emerged as one of the reliable source of electricity. It is estimated that around 500 small hydropower stations were generating electricity worldwide by 1910. Large hydro stations were built in the United States and USSR in 1930s. Nuclear power for electricity generation gained attention in 1950s and developed nations increased their electricity production to attain sufficiency. In 1973, oil embargo took place and oil price from middle-east quadrupled which shook the world economy and development process. After learning about oil embargo, policies related to oil prices were formulated. “Energy conservation”, “energy efficiency” and “energy diversification” were the most favored words and different sources of continued supply of energy were sought. Increased research on air pollution, global warming and Ozone layer depletion along with formation of Intergovernmental Panel on Climate Change (IPCC) and United Nations Framework Convention for Climate Change (UNFCCC) tried to push for transition of energy sources from conventional to non-conventional ones. The concept of sustainability gained attention across the nations and developed countries adopted renewable energy for electricity production to make their clean and green. From Wind to Solar, and now shift towards hydrogen is seen as a way to attain Net zero targets and achieve the energy transition towards clean and green future [13]. Global energy demand increased 10 times from 1.4 billion tons of oil equivalent (toe) to 14.4 billion toe from 1925 to 2019. Since 2010, global energy technology change has changed significantly with the decreased cost of photovoltaic power generation, wind power, etc. Since then, photovoltaic power generation will increase from 32 billion kwh to 699 billion kwh, an annual increase of 240%, wind power generation increased from 342 billion kwh to 1404 billion kwh (annual increase of 45%) [20]. At present, wind energy has reached its zenith and solar is growing manifolds but due to their intermittency issue and huge storage cost, hydrogen is seen as the fuel of tomorrow. Air pollution, increasing fuel price and import dependence are other important pushes for India to move towards hydrogen economy. These push factors are discussed below:

2.1

Air Pollution

Deteriorating air quality is driving the transition towards cleaner and greener fuels. Studies have noted that 18% of primary energy use and 17% of global CO2 emissions are contributed by transport sector especially road transport. Transportation sector is also responsible for 20% of projected increase in both global energy demand and GHGs emissions till 2030 [4]. A recent study based in India provides a critical

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assessment of hydrogen use in Indian transportation sector and highlights the need of national hydrogen energy road map to achieve the cost target of 0.5$/kg of hydrogen as fuel. Hydrogen energy is emerging as reliable, clean and efficient energy carrier which can ensure energy security [1, 14]. For this reason, many nations are shifting towards hydrogen specifically for transportation sector. Japan, Germany and the United States have the highest number of hydrogen stations. Europe is estimated to have 3,700 refueling stations and a fleet of 3.7 million passenger fuel cell vehicles [9]. Hydrogen helps to avoid negative impact of air pollution and has potential to reduce global warming [2] and ozone layer depletion [8].3 Even wheel to tank studies and evaluations [7] have shown hydrogen emits less emission as compared to other fuels.

2.2 Increasing Fuel Prices and Economic Burden From all the stocks of fossil fuels, crude oil remains the most consumed and globally traded [22] and this dependence on crude oil consumption is leading to environmental changes which in turn is putting pressure on governments across the nations to shift towards the cleaner fuels [33]. India is one of the top importers of crude oil after China and the United States. Economic Survey of India [12] estimated rise in GDP at 8.0–8.5% in 2022–23, if the oil prices remain in range of US$70–75/bbl. Crude petroleum oil import is one of the highest imported commodities in India, which has doubled to US$ 73.3 billion in April-November 2021. Figure 2 gives a clear picture of current scenario of crude oil and petroleum product imports by India. The data has shown steady increase in oil import till 2019. Affected by COVID-19 pandemic for some time, oil import has again observed a rise in 2021–22. In monetary terms, India’s bill for oil import has increased from USD 62.2 billion (2020–21) to USD 119.2 billion (2021–22) (data from PPAC). To reduce this dependency on oil import, there is a critical need for India to shift towards sustainable and local fuels, and Hydrogen demands to be one of the most promising among those fuels. There is an urgent and actionable recommendation to governments and industries to scale up technologies and bring down costs to allow hydrogen to become widely used.

3 Hydrogen Energy: Leading the Transition Hydrogen usage varies according to output required. It can be used as chemical feedstock in various industrial processes, fuel cell [27] for electricity generation or can be used directly through direct combustion. The main uses of hydrogen produced by industries are oil refining (33%), ammonia production (27%), methanol production 3

Bicer, Y., & Dincer, I. (2017). Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel. International Journal of Hydrogen Energy, 42(6), 3767–3777.

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Import of crude oil and petroluem products ('000 metric tonnes) 3,00,000 2,50,000 2,00,000 1,50,000 1,00,000 50,000 0

Crude oil

Total import

Fig. 2 Import of crude oil and petroleum products (in ‘000MT). Source data retrieved from [26]

(11%) and steel Production via direct reduction of iron ore (3%). Hydrogen is mainly produced from conversion of natural gas (approx. 75%) and coal (approx. 20%) and 2% from electrolysis [17]. Hydrogen is produced by many ways and according to its production mechanisms, it is categorized into various shades (i.e., blue, green and grey). Green hydrogen uses renewable energy like solar or wind in electrolysis of water for the hydrogen production and thus cleanest of all. Using renewable energy for hydrogen production may increase the interconversion of electricity Grey hydrogen uses fossil fuel i.e., natural gas, coal and methane, for hydrogen production which leads carbon dioxide emissions in the atmosphere, and blue hydrogen is produced using natural gas using steam reforming method. During this method, hydrogen and carbon dioxide are produced. This carbon dioxide is captured and stored for further use. Other not-so-prominent shades of hydrogen include, pink, turquoise, brown, yellow and white. Pink hydrogen is produced by electrolysis powered by nuclear energy. Turquoise hydrogen uses methane pyrolysis process using natural gas. Brown hydrogen uses steam methane reforming process powered by coal which produces carbon dioxide emissions. Yellow hydrogen uses solar energy for electrolysis [24]. So far in the industrial scale, large quantities of Hydrogen (∼95%) are being produced from fossil fuels by Steam-methane reforming process, or partial oxidation of methane and coal gasification. As of 2020, this process is considered as current leading technology for Hydrogen production, whereas only a small quantity of Hydrogen is produced by other routes such as biomass gasification or electrolysis of water [25, 30]. Electrolysis method may use wind, solar, geothermal, hydro, fossil fuels, biomass, nuclear and many other energy sources for hydrogen production, and this method is being studied as a viable way to produce hydrogen domestically at a low cost. The hydrogen energy can be used for all practical needs with high energy efficiency, overwhelming with environmental and social benefits and also economic competitiveness [10]. Presently, hydrogen is already used as fuel and feedstock in various sectors, but to remain in race to reach Net zero targets major shift towards hydrogen in refining petroleum, ammonia industry, power sector, feedstock

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for methanol production, steel industry, long haul freight and heavy-duty vehicles. International Energy Agency (IEA) projects an increase in hydrogen demand from 287 mt (sustainable development scenario) to 528 mt (Net zero Scenario) which can result in mitigation of 1.6–3.5 mt of GHGs emissions annually by 2050 (IEA, 2021). For a smoother transition towards hydrogen economy especially the green hydrogen, a shift or overhaul of complete system is required to ensure it is well accepted by all stakeholders. At present, R&D on applicability of Hydrogen as substituted fuel has just begun. There are various challenges which need to be catered for smooth energy transitions [3]. Lack of policies, under developed financial mechanism, slow market readiness and inadequate infrastructural developments are identified as impediments in road of hydrogen economy [18]. For smoother transition, the abovementioned challenges need to be catered. The transition will include setting up of institutions, developing supply chains, formation of physical infrastructure, R&D and favorable policies. Public participation and engagement in policymaking around hydrogen energy are equally important to ensure its diffusion especially in transportation sector. The acceptance of hydrogen among the social system will depend on how hydrogen is made relatively advantageous when compared to other energy source. Therefore, science-policy interface needs to be dealt swiftly to smoothen the adoption of hydrogen and mission-oriented approach which combines bottom-up and top-down perspectives needs to be considered [14]. India has taken multiple initiatives to attain Net zero carbon emissions by 2070. The National Hydrogen Mission as has been announced by Prime Minister Mr. Narendra Modi on the 75th Independence Day Celebrations in August 2021 is considered to be the country’s first major step to achieve the climate targets and green hydrogen adoption. Figure 3 describes that the policy has the several important targets to fulfill to convert India to a zero-carbon hub.

4 Co-evolution of Science, Technology and Innovation Policies and Hydrogen Energy in India In the pursuit of transition towards hydrogen economy, India will be heavily dependent on new technologies for hydrogen production. This technological change can be considered as an evolutionary process. In this, new technological alternatives will compete with each other and also with already existing practices for survival. Renowned STS scholar [5] has also argued that the development of technology is best understood as an evolutionary process. Adoption of technology is dependent on quality and relevance i.e., best technology is more adopted as compared to inferior ones . Other STS scholars like Bijker, Hughes and Pinch (1987) emphasize that political and economic power of particular groups determine the adoption and persistence of technology. Rogers [28] defined technology diffusion as “the process in which an innovation is communicated through certain channels over time among the members of a social system (p. 5)”. He recognized four elements which make the diffusion

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Fig. 3 The 25-year road map for Green hydrogen Adoption in India. It depicts that different sectors have been emerged as a priority to combat the global warming. Source NITI Aayog

process possible i.e., an innovation, communication through communication channels, at given time and the social systems. The various characteristics of innovation which determine the rate of adoption are (pp. 15–16): 1. Relative advantage: It is the degree to which new technology is better than older one (which will be replaced). It can be in terms of money, convenience, satisfaction and prestige. A new technology or innovation will be adopted only if it is advantageous over existing technology. 2. Compatibility: It is identified as the degree to which an innovation is perceived as consistent with existing values, past experiences and needs of potential adopters. 3. Complexity: It is the degree to which a new technology/innovation is different and complex to use. If a technology is user friendly and simple then it will be more adopted. 4. Trialability: It is degree to which an innovation or new technology can be tried on installments or safe to use. 5. Observability: It is extent to which results of an innovation can be observed by others. If positive effects of energy efficient technology in the form of reduced electricity bills, reduced emissions, etc. can be easily observed by the population,

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it will be more adopted. Therefore feedback becomes highly important to ensure better diffusion. It is important to note that Hydrogen technology is not new but as its use has renewed and that is why it is relevant to understand the path of adoption of hydrogen technology. Taking a cue from co-evolutionary theory of technology, authors propose that hydrogen energy technology adoption will not only depend on its technical efficiencies rather social, political and economic criteria as well. It is quite early to predict the path of diffusion of hydrogen technology in India but given the present policy push by government of India, its adoption scenarios are good. For hydrogen energy technology, co-evolutionary perspective is relevant to understand as various environmental issues i.e., climate change, global warming and extreme weather conditions are leading to change policies across the world, and countries are making emissionreducing goals which in turn are pushing towards adoption of newer and cleaner technologies. As also discussed by Norgaard (1994), co-evolutionary theory depends on the interaction between knowledge, values, organization, technology and environment. Although co-evolutionary change could be path-dependent, leading to historical lock-in of technologies, institutions and environments (natural and human), it should not be confused as being synonymous to positive feedback, dynamic change, mutual adaptation or path dependency [19]. Stagl (2007) explores three layers of co-evolutionary processes in terms of sustainable development i.e., “co-evolution of the environment and governance, co-evolution of technology and governance, and co-evolution of human behaviour and culture”. It also involves relationships between entities which in turn affect the evolution of entities and ongoing positive feedbacks between components of evolving systems [19]. It needs to be noted that trajectory of technological change is not influenced as much by newer inventions, but by social change [6] therefore, changes in technological systems require paradigm shifts, which are made possible through changes in the social behaviors. Along with technologies, right policies at the right time are also important for better adoption of hydrogen technology and smoother transition towards hydrogen economy. Policies especially Innovation policies have become an integral and legitimate part of economic policy since 1980s in India. These policies are relevant for human capital, social capital, economic development and creation, management and flow of knowledge in a country. It has become relevant for all the countries alike as now a days international agenda concerns knowledge economy and sustainable development. Science, Technology and Innovation (STI) policies lead to development of concept of whole innovation system i.e., institution, organization and learning mechanisms. STI policy scholars emphasize that STI policy will play crucial role in sustainability transitions and therefore they should be developed for strategic management of transitions [21]. Indian policymaking for science and technology started taking shape only after year 2000. India introduced its first Science and Technology Policy in 2003 followed by Science, Technology and Innovation Policy in 2013 and 2020. The first Science Policy however was introduced in 1958 as a “Scientific Policy Resolution” which laid down foundation of scientific enterprise and scientific temper in India. Investment

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in science and technology was realized as a mechanism for growth and development and an instrument of socio-economic transformation. Later in 1983, Technology Policy Statement (TPS) was presented by government for technological self-reliance through promotion and development of indigenous technologies. Technology development in information, electronics and biotechnology sector was given emphasis for betterment of society. TPS 1983 underlined the need of technology forecasting and assessment studies of emerging and current technologies. Science and Technology Policy 2003 brought science and technology together and highlighted the need of R&D investment. It highlighted the need of integrating socio-economic sectors with national R&D system for national innovation system creation. Science, Technology and Innovation Policy (2013) introduced the term “innovation” in its policy document as an instrument of policy. It focused on prioritizing the R&D in field of agriculture, energy, water management, telecommunications, health and drug discovery and climate change. Establishing national innovations systems through funding, knowledge management and training. The hydrogen policy (2022) of India provides for purchase of renewable power from power exchange by green hydrogen/ ammonia manufacturers and these manufacturers can keep its unconsumed renewable power for 30 days with distribution company and also take it back when required. Inter-state transmission charges are allowed to be waived off to the manufacturers of green hydrogen and green ammonia for 25 years. National hydrogen mission of India focuses on blending hydrogen with CNG as transportation fuel and industrial input to refineries.

5 Financing Mechanism Towards Hydrogen Energy Transitions As per IPCC sixth Assessment Report, a global carbon budget of 400 GtCO2 is required to limit the temperature rise to 1.5 °C with a 67% likelihood by 2050. Hydrogen projects are capital intensive and highly sensitive to borrowing interest rates and income tax rates and other finance costs [31]. India is gradually developing a robust sustainable finance mechanism to finance the clean and green energy projects. In 2021, a Task Force on Sustainable Finance (TFSF) was set up to define the framework for sustainable finance, identifying and establishing the pillars for sustainable finance roadmap. It also aims to suggest the draft taxonomy of sustainable activities and a framework of risk assessment by financial sector. The Reserve Bank of India (RBI) has joined the Central Banks and Supervisors Network for Greening the Financial System (NGFS) on April 2021. The liberalized External Commercial Borrowings (ECBs) norms of RBI have enabled the renewable energy companies and other firms to take the ECB route for raising finance through green bonds and sustainable bonds. For Hydrogen sector, green hydrogen policy has highlighted the need of financial support to hydrogen manufacturers by exempting the payment of Inter-state transmission charge (ISTC) on renewable energy bought by

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projects which are commissioned by June 2025. The investment in green hydrogen production is set to cross $1 billion per year by 2023 and also the investment in electrolysis is booming around the world. These initiated a fall by 40% in the Green hydrogen production cost since 2015 and is expected to fall by a further 40% through 2025.

6 Conclusion Hydrogen Energy transition in India is a long process which needs technology, R&D, funding and policies support from government. Whereas at receiver’s end, public needs to be more aware and participate in policymaking, they would be required to change the behavior in order to accept the technology. Therefore, in a concluding remarks, it can be said that Hydrogen being a leading and most promising source of energy should be considered in various key sectors as a major source of energy. In this regard, the establishment of policies to stimulate commercial demand of clean Hydrogen to reduce the production of Green House Gases plays a key factor. Over the next few decades, R&D should establish criteria to lower the cost for Green hydrogen production. Also focus has to be made to enhance the infrastructure development, investor’s confidence and establishment of shipping routes for international hydrogen trade.

References 1. Apostolou D, Xydis G (2019) A literature review on hydrogen refuelling stations and infrastructure. Current status and future prospects. Renew Sustain Energy Rev 113:109292 2. Apostolou D, Welcher SN (2021) Prospects of the hydrogen-based mobility in the private vehicle market. A social perspective in Denmark. Int J Hydrogen Energy 46(9):6885–6900 3. Bellaby P, Flynn R, Ricci M (2006) Major change, its risks and the part ‘trust’ might play in managing them: comparing the current pensions crisis and the impending energy crisis. UKSHEC Social Science Working Paper No. 17. ICSPR, University of Salford. Available from: www.psi.org.uk/ukshec/publications.htm#workingpapers 4. Ball M, Wietschel M (2009) The future of hydrogen–opportunities and challenges. Int J Hydrogen Energy 34(2):615–627 5. Basalla G (1988) The evolution of technology. Cambridge University Press 6. Beder S (2000) Costing the earth: equity, sustainable development and enivronmental economics. NZJ Envtl. L. 4:227 7. Bethoux O (2020) Hydrogen fuel cell road vehicles and their infrastructure: an option towards an environmentally friendly energy transition. Energies 13(22):6132 8. Bicer Y, Dincer I (2017) Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel. Int J Hydrogen Energy 42(6):3767–3777 9. Dash SK, Chakraborty S, Roccotelli M, Sahu UK (2022) Hydrogen fuel for future mobility: challenges and future aspects. Sustainability 14(14):8285 10. Dixon RK (2007) Advancing towards a hydrogen energy economy: Status, opportunities and barriers. Mitig Adapt Strat Glob Change 12:325–333

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11. Edquist C (2011) Design of innovation policy through diagnostic analysis: identification of systemic problems (or failures). Ind Corp Chang 20(6):1725–1753 12. Economic Survey of India (2022) 13. Edwards PP, Kuznetsov VL, David WI (2007) Hydrogen energy. Philosophical transactions of the royal society a: mathematical. Phys Eng Sci 365(1853):1043–1056 14. Falcone PM, Hiete M, Sapio A (2021) Hydrogen economy and sustainable development goals: review and policy insights. Curr Opinion Green Sustain Chem 31:100506 15. Foley G (1976) With Charlotte Nassim and Gerald leach (1976) The Energy Question, Penguin books ltd., England 16. Fred Cortell in his book “Energy and Society” emphasized on relation of energy, its consumption with society. For details refer to Cortell F (1970) Energy and society, Green word Press, Connecticut 17. French S (2020) The role of zero and low carbon hydrogen in enabling the energy transition and the path to net zero greenhouse gas emissions: with global policies and demonstration projects hydrogen can play a role in a net zero future. Johnson Matthey Technol Rev 64(3):357–370 18. Kar SK, Sinha ASK, Harichandan S, Bansal R, Balathanigaimani MS (2022) Hydrogen economy in India: a status review. Wiley interdisciplinary reviews: energy and environment, e459 19. Kallis G (2007) When is it co-evolution? Ecol Econ 62(1):1–6 20. Kong F (2022) A better understanding of the role of new energy and green finance to help achieve carbon neutrality goals, with special reference to China. Sci Prog 105(1):00368504221086361 21. Kemp R, Schot J, Hoogma R (1998) Regime shifts to sustainability through processes of niche formation: the approach of strategic niche management. Technol Anal Strat Manag 10(2):175–198 22. Khan SAR, Ponce P, Thomas G, Yu Z, Al-Ahmadi MS, Tanveer M (2021) Digital technologies, circular economy practices and environmental policies in the era of COVID-19. Sustainability 13(22):12790 23. Lutzenhiser LC (1994) Sociology, energy and interdisciplinary environmental science. Amer Sociologist, spring, pp 58–70 24. Maurya V (2022) India’s Transition towards a hydrogen economy. The Statesman. https://www. thestatesman.com/opinion/indias-transition-towards-hydrogen-economy-1503094363.html 25. Ogden JM (1999) Prospects for building a hydrogen energy infrastructure. Annu Rev Energy Env 24:227–279. https://doi.org/10.1146/annurev.energy.24.1.227 26. Petroluem, planning and Analysis Cell (PPAC) website accessed from https://www.ppac.gov.in/ on 28th September 2022 27. Ponnusamy P, Panthalingal MK, Pullithadathil B (2022) Technological risks and durability issues for the proton exchange membrane fuel cell technology. PEM Fuel Cells, pp 279–314 28. Rogers EM (2003) Diffusion of innovations. The Free Press 29. Rosa et al (1988) Energy and society. Ann Rev Sociol 14:149–172 30. Roberts D (2018) This company may have solved one of the hardest problems in clean energy. Vox. Retrieved 2019-10-30. 31. Taghizadeh-Hesary F, Li Y, Rasoulinezhad E, Mortha A, Long Y, Lan Y, ... Wang Y (2022) Green finance and the economic feasibility of hydrogen projects. Int J Hydrogen Energy 32. World Energy Outlook (2012) Factsheet: How will global energy markets evolve to 2035, World energy outlook, OECD/Paris 33. Wang KH, Su CW, Umar M (2021) Geopolitical risk and crude oil security: a Chinese perspective. Energy 219:119555

Sustainability: An Imperative Gauri Jauhar

Abstract In the language of design and systems design, we are confronted with a “wicked” problem of sustainability, with a capital S. The path out of addressing the effects of climate change, appears non-linear, uncertain, and material. Energy and economic choices may well collide with climate constraints. Firmly rooted in the complexities of the inter-related energy and economic systems, sustainability has over the last year reached the boiling point of a Net zero future articulated by countries and companies. Approximately 90% of global greenhouse gas (GHG) emissions are covered by Net zero pledges, but with different strength and timing. In the quest for the planetary balance that is central to Net zero ambitions, India and India Inc are no exceptions. The classic dilemma of development and its associated carbon footprint, that are foundational to our energy mix and choices, exists. Learning objectives: • Development and environment sustainability • Net zero and technology choices • Energy transition and economic linkages Keywords Climate change · Planetary balance · Sustainability · Energy transition · Net zero

Abbreviations CCUS GHG IPCC SEC

Carbon Capture, Utilization and Storage Greenhouse Gas Intergovernmental Panel on Climate Change Securities and Exchange Commission

G. Jauhar (B) Energy Transitions and Clean Tech Consulting, S&P Global, Plot 3, Ambience Corporate, Tower-2, Ambience Island, Gurugram 122002, India e-mail: [email protected]; [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Goel and G. Sen (eds.), Climate Action and Hydrogen Economy, Green Energy and Technology, https://doi.org/10.1007/978-981-99-6237-2_7

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Fig. 1 Development and sustainability (Source www.unsplash.com)

1 Context of Sustainability: An Evolving View In the language of design and systems design, we are confronted with a “wicked” problem of sustainability, with a capital S. In the 1970s, two design theorists, Rittel and Weber [1], characterized problems such as sustainability as “wicked”, being difficult to solve, with trying timelines and the challenge of coordinated action across stakeholders. Solutions and sources of emissions causing climate change impacts are often on the same side of the equation, and the tendency to prioritize the present over the future (hyperbolic discounting) exists. Hence the path out of addressing the effects of climate change, appears non-linear, uncertain, and material. Energy and economic choices may well collide with climate constraints (Fig. 1).

2 “To Be, or not to Be, that is the Question…” Shakespeare, Hamlet Since the late 1980s with the setting up of the Intergovernmental Panel on Climate Change (IPCC) and then the Kyoto Protocol of the early 1990s, sustainability has been coming into sharper focus. The very existence of our species, to be or not to be, in the evergreen words of the great bard has acquired dimensions of greater breadth and depth. In the mid-2000s, as the impact of the US shale revolution was gaining strength for energy supplies, the focus on sustainability was growing sharper. Just about then, there were 3 things that left a mark on the young energy professional in me that was making the shift from roughly a decade in the energy sector in North America to the one in Southeast Asia. It was in the mid-2000s also, an online calculator on carbon footprint was launched by bp, Al Gore’s Inconvenient Truth [2] casts a strong light on climate, and I interacted with a wider professional community

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at a young leader’s program in Germany, organized by the Bucerius Summer School. I started thinking about sustainability beyond the sustainability of an energy company’s financial strategy during the booms and busts of commodity and economic cycles. The latter was where bulk of my training and experience resided, so far. So, this was new. I knew now there was something far wider that had to be factored in. The word “sustainability” had acquired a meaning greater than jargon, and one that needed the swift attention of companies and countries as it linked to growing climate realities. Climate change, with each passing decade, has gained the attention of a wider spectrum of stakeholders, in a bid to prevent a market failure in addressing its challenge to sustainability. The Paris Climate Agreement of 2015 was a watershed event, which increased pressure for climate-related financial risk disclosure. Post Paris, the Task Force on Climate Disclosures was established by the Financial Stability Board, has 31 members and has been adopted by a broad range of sectors, with a total market capitalization of $26 trillion and financial institutions responsible for assets of $220 trillion. The next stage to this push for disclosures has been the focus on climate-related financial risk reporting with the Securities and Exchange Commission (SEC) 2022 proposal that seeks standardization in companies’ mandated emissions reporting.

3 Sustainability and Net Zero: A Framework of Ambitions and Choices Firmly rooted in the complexities of the inter-related energy and economic systems, sustainability has over the last year reached the boiling point of a Net zero future articulated by countries and companies. Approximately 90% of global greenhouse gas (GHG) emissions are covered by Net zero pledges, but with different strength and timing. Energy companies are increasingly announcing a range of Net zero targets on the nature of emission reductions (scope 1, 2, 3) and are under increasing pressure from investors to demonstrate a Paris climate aligned path of reduction in emissions. In the quest for the planetary balance that is central to Net zero ambitions, India and India Inc are no exceptions. The classic dilemma of development and its associated carbon footprint, that are foundational to our energy mix and choices, exists. In this, India Inc as shown by the Net zero ambition of more than two dozen companies is noteworthy. These companies [3] include Indian Oil Corporation, Reliance Industries, HDFC Bank, Tata Consultancy Services, Wipro, Infosys, Indian Railways, ITC, ACC, Dalmia Cement, Ambuja Cements, Arcelor Mittal, Nippon Steel, Essar Oil & Gas, Sun Pharma, Vedanta Ltd, Piramal, Nayara Energy, ReNew Power, SRRungta Group, DR. Reddy’s, Hindustan Power, JSW Steel, Suzlon, AM/NS India, SRF, Tata Chemicals, Adani Transmission, Tata Motors, Tech Mahindra, Mahindra Rise. While India Inc can accelerate on the Net zero path by the right portfolio choices, India as a country with its 2070 target reflects the balance of climate ambition and climate justice.

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4 Sustainability and Energy Transition: Economic Linkages and Technology Choices As this seeming dichotomy of the path to Net zero of India Inc and the Indian economy plays out, these are areas for consideration for the boardroom and the policy maker, alike. 1. Understanding energy transitions and their linkage to economic transitions: For the global energy system to achieve Net zero, large Asian emitters like India are key due to the size of the population, high sustained economic growth rates and associated development goals. Understanding the energy transition of the world’s 5th largest economy, on the pathway to being its 3rd largest economy, requires a keen economic lens to frame the Indian energy transition. The economic transition of India will transform where people live, how people move, how reliable people’s lives become in an increasingly market-led and market-based framework. These economic transitions are a mobility transition, an urbanization transition, a reliability transition held together with the inevitable march towards markets. The story of each of these transitions is the story of the unfolding energy transition in India. India’s mobility transition is one of a move on the S-curve of four-wheeler concentration as the reliance on two wheelers and three wheelers moderates with increasing economic prosperity. India’s urbanization transition is one of a move of a population from rural India to urban India and the closing gap in access to energy, as urbanization proceeds. India’s reliability transition relates to the growing cross-sectoral demand for and supply of reliable, 24/7 power. These transitions will impact the demand trajectory of fuels and bring about a greater inter-fuel competition at the energy product level of gasoline, diesel, gas, hydrogen, LPG, Jet fuel, bitumen, kerosene, and the infusion of technologies such as batteries for storage and Carbon capture, utilization, and storage (CCUS). There will also be a growing role for support from energy efficiency and circular economy technologies, which will largely rely on better consumption options and choices, which bring in micro-level energy savings, even as energy demand grows with population and economic transitions (Fig. 2). 2. For the Indian economy, a Net zero future will require putting a value on clean air by enacting a sufficient carbon price mechanism that can alter fuel choices and phase-down the high-carbon lock-in of the Indian energy mix. Putting a value on clean air, and carbon in the context of development needs will enable optimizing the value-price–cost equation, key to be solved for sustainability to be actionable. The coal cess mechanism, a de facto carbon price, has not been sufficient to alter the use of coal and incentivize cleaner fuels. For India Inc’s boardroom, this will imply carbon pricing entering project stage gates of approval and decision-making. The Indian government’s recent launch of the initiative to create a framework for a national carbon market is a step in the right direction. India being a leader in the location of carbon offsets, also provides a physical underpinning for the creation of a national carbon market.

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Fig. 2 Four key economic transitions (Source Author’s conceptual framework)

3. Technologically, India has an opportunity to leapfrog in the next generation of material-impact low carbon technologies like Hydrogen and CCUS. As a world leader in refining and petrochemical capacity, India Inc can accelerate the hydrogen economy across the value chain. In carbon capture, there are case studies of innovation by companies with local engineering talent such as Carbon Clean [4] that are deploying technology globally and in India. India’s talent advantage of world class engineers can meet the needs of accelerating and innovating on low carbon technologies.

5 Sustainability: Need for an Energy Systems Approach Senge [5], a key proponent of systems thinking and author of the book The Fifth Discipline: The Art & Practice of The Learning Organization states, “Reality is made up of circles, but we see straight lines”. The need of the hour is to adopt that circular, systemic approach to Sustainability in the board room, and in policy making. Ultimately, an energy systems approach would have to be pervasive where several global, national, sub-national points of influence and optimization of carbon pricing, energy choices, economic choices, cost of capital will resemble a large non-linear programming problem where the impacts of climate change and local air quality will manifest in cross-sectoral pathways.

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6 Conclusions Sustainability and energy transitions will require a holistic, systems-thinking approach of how the energy transition will be a function of economic transitions and related technology adoption options and choices. A value on carbon and establishing carbon markets will be critical to triangulating prices, costs, and value on the path to Net zero and sustainability. Solving for several global, national, sub-national points of influence and optimizing carbon pricing, energy choices, economic choices, cost of capital will resemble a large non-linear programming problem where the impacts of climate change and local air quality will manifest in cross-sectoral pathways.

References 1. Rittel HWJ, Webber MM, Dilemmas in a general theory of planning 2. Al Gore: An inconvenient truth: the planetary emergence of global warming and what we can do about it 3. Corporate net zero announcements 4. Carbon Clean. www.carbonclean.com 5. Senge PM, The fifth discipline: the art & practice of the learning organization

Hydrogen Production Technologies

Solar Light-Triggered Hybrid Approaches for Green Hydrogen Girivyankatesh Hippargi and Sadhana Rayalu

Abstract In COP26 summit-2021 in Glasgow, India made commitment to replace 50% of its fossil fuel/coal technology with green fuel by 2030. The process for the conversion of water into hydrogen using full spectrum of natural sunlight needs longterm strategy. This chapter provides glimpses of approaches pursued by our group being pursued to address the ongoing technical issues and shortfalls for hydrogen generation technology. This is being pursued by implementing different strategies such as newer design of hybrid materials and systems, increased solar to hydrogen conversion efficiency and scaling and piloting technology. Plasmonic bimetallic AuPt, Cu-Pt and Ag-Pt titania composites have been developed and tested for photocatalytic water splitting in photovoltaic (PV) panel coupled 30 Ltr capacity photoreactor system showing hydrogen evolution rate (HER) ranging from 12 mmol/h/400 mL to 17 mmol/h/400 mL which is exemplary by considering the uses of solar generated energy. Functional PV-based facilitated Water Electrolyzer (WE) system is showing promising leads of HER of 1.12 L/min. Learning objectives: • Production of green hydrogen using solar light • Hybrid approaches to increase hydrogen conversion efficiency • Integration of solar hydrogen in the fuel cells and research achievements at NEERI, Nagpur Keywords Photocatalytic water splitting · Photothermal · Hybrid processes · Hydrogen evolution rate

Abbreviations CA

Carbonic Anhydrase

G. Hippargi · S. Rayalu (B) Environmental Materials Division, CSIR-National Environmental Engineering Research Institute, Nagpur 440020, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Goel and G. Sen (eds.), Climate Action and Hydrogen Economy, Green Energy and Technology, https://doi.org/10.1007/978-981-99-6237-2_8

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DST FPV HER IR Ni2P PV PEM SUN WE

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Department of Science and Technology Functional PV panel Hydrogen Evolution Rate Infrared Nickel Phosphide Photovoltaic Proton Exchange Membrane Solar Energy Utilization Water Electrolysis

1 Introduction Global energy demands together with their probable environmental impact are projected to continue rise in the coming years and shall remain in central scenario. Global primary energy consumption is predicted to be double by 2050 [1]. The incessant growth of population and industrial sector are two leading factors responsible for this higher energy requirement. These issues will result in an upsurge in the cost of energy and renewed anxieties about the security of the energy supply and climate change. The issue of climate change with consequent continuous threat of global warming is leading to devastating impacts including rising sea levels, flooding and severe droughts, widespread food and water shortages and more destructive storms. The global scientific community has reached a strong consensus that the threat of climate change and the connection between fossil fuel utilization and the greenhouse effect are substantial enough to rationalize massive efforts to shift from conventional energy resources in the coming years. To find a solution together, in December, 2015 global level representatives of 195 countries participated in the United Nations Climate Change Summit at Paris and passed the agreement to reduce carbon output by cutting down the greenhouse gas emissions to keep global warming temperature below 2 ºC. To fulfill the agreement passed at Paris, countries need to establish concrete steps for reducing their emissions and focusing on an alternative energy system to replace fossil fuels. A number of recent studies suggested that the direct use of hydrogen as a fuel may deliver a much cleaner and far less expensive fuel substitute [2]. Engines that burn hydrogen produce almost no pollution. It has potential to provide both clean and renewable energy with simultaneous environmental protection from greenhouse gases. Currently, hydrogen is being produced for commercial and industrial purposes in large quantities using fossil fuels like petroleum feedstocks, natural gas, coal and nuclear energy [2, 3]. Thus, challenge is to produce hydrogen from renewable resources. In this context, solar energy is emerging as the largest source of all energy sources and has untapped capability well beyond its present usage for centralized and decentralized applications. By using the renewable energy source such as solar radiation/energy, we can generate clean energy source such as hydrogen. The

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recent reports suggest that, hydrogen production has significant opportunities in the following areas—(i) photocatalytic water splitting hydrogen [4, 5] (ii) electrochemical or photoelectrochemical water splitting hydrogen [6] and (iii) Photothermal or photothermocatalytic water splitting hydrogen. Although, these techniques are successful at laboratory scale, the major challenge is to operate the system on natural sunlight. Photocatalysis is still facing issues of poor yield, technical glitches and purity of hydrogen. Contrary, electrochemical is successful and scaled for commercial operation, however, the way for operating the system on renewable energy and other factors such as higher cost, efficiency, durability are still the major challenges. Photothermal has potential to utilize the abundant heat available in solar spectrum, however, the challenge is to deliver the technology and system for effectively harvesting solar heat. Another major challenge is the operation at fluctuated and higher temperature and pressure. Hence, photothermal system can be used only by coupling with other system. In this context, alternative or hybrid approach of solar energy conversion systems is appearing to be potential future technology. These hybrid approaches include (i) PV-based systems for conversion of solar energy into electricity, which in turn, drives water electrolysis to split water into hydrogen and oxygen; (ii) design of PEC or photocatalytic systems wherein water splitting reactions are driven directly by light, without the need to separately generate electricity and (iii) photothermal systems to provide heat and photons to mixture of water and donor to facilitate photothermal reforming of donor or chemical reactions such as oxidative hydrolysis of zinc etc. The photocatalytic, PEC and photothermal approaches, hold potential for accomplishing simplified systems and/or high-energy conversion efficiencies, however, they require considerable development for translation from lab-scale prototype to pilot scale and commercially viable systems. The issues and challenges addressed and initiatives undertaken by our group to reduce the large gap between present laboratory demonstrations and deployable technology include a. Photocatalytic (i) Design of broadband absorption material [7], (ii) Utilization of low-cost donors (preferably waste like sulphides, urea, glycerol or bio-ethanol) with comparable properties to alcohol for enhancing the net energy recovery [8]; (iii) Increasing the solar to light efficiency for photocatalytic pure and donor-assisted water splitting reaction; (iv) Enhancing photocatalyst stability. b. PV-based water electrolysis (i) Reducing cost of the catalyst by replacing or minimizing Pt content; (ii) Extending device lifetimes; (iii) Reducing costs of electrolyzers; (iv) Design of broadband absorption novel reactors for maximizing energy efficiency and minimizing efficiency loss in scale-up systems. c. Photothermal photocatalytic and photothermal hybrid technology to utilize the neglected IR spectrum of sunlight

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This chapter provides glimpses of shortfall issues and approaches being pursued and work undertaken by our group on future technologies for the artificial production of solar hydrogen.

2 Photocatalytic Water Splitting The concept of photocatalytic water splitting is inspired by the photosynthesis process. It works in the same manner as in plant photosynthesis process [9] (Fig. 1) and therefore recognized as a perfect system capable to provide clean and renewable energy source in single step. It utilizes cheap and abundant input energy source/raw materials such as sunlight and water and photocatalytic material in suspended form to deliver green hydrogen. It is a heterogeneous photocatalytic reaction in which photons are incident on artificial light absorbers, resulting in the generation of electronically excited states that are immediately used to drive thermodynamically uphill chemical reactions. This process converts electrical energy into chemical energy to produce hydrogen. This makes the whole process cyclic and non-polluting. Therefore, for the large-scale hydrogen production, water splitting photocatalyst systems are considered to be advantageous over more complex multilayer or tandem structure devices [10–12]. However, the energy conversion efficiency has remained much lower compared to that of photovoltaics. Thus, the improvement of efficiency trusts upon novel materials for efficient solar energy harvesting for hydrogen evolutions. In recent years, several new materials and approaches with increased water splitting efficiency emerged on global platform [13]. Heterogeneous photocatalytic process involves following three major steps, 1. adsorption of molecule on the photocatalyst surface, 2. chemical transformation of molecule while visiting several reaction sites at the surface by diffusion and 3. subsequent desorption of the intermediate or product molecule to the liquid/gas phase. The critical challenge of this artificial photosynthesis is that it has not been demonstrated in an effective, robust and commercially feasible form particularly, due to lower hydrogen output and technical glitches. Although continuous efforts are on radar to resolve the issue by materials tailoring, noble metal loading, metal/non-metal doping, dye sensitization, composite semiconductor, addition of sacrificial organic or inorganic donor, the way for the commercially acceptable single-step photocatalytic water splitting is still far from the reality. To overcome the issue and to meet the urgency clean energy goal at this juncture, the current trends are shifting toward hybrid system by coupling the photocatalytic water splitting system with photovoltaic or photoelectrochemical cell. Baniasadi et al., reported the hybridization of photocatalytic process with multi-catalysts and electric potential bias to improve the output of the reactor and reaction rate. This

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Fig. 1 Difference between a natural photosynthesis [9] and b artificial water splitting photocatalytic process

work reports HER of 0.41 mmol/h with 0.75(v/v) ZnS under one sun in a hybrid reactor. This rate is twice as high as that achieved with 0.2% v/v CdS, indicating the superior performance of cadmium sulfide and zinc sulfide photocatalyst [14]. Temblay et al. presented the Nonmetallic abiotic-biological hybrid photocatalyst for visible water splitting by coupling C3 N4 with H2 O2 degrading bovine catalase which improved the solar to hydrogen efficiency by 3.4% with hydrogen evolution rate up to 55.72 μmol h−1 [15]. Guo et al. reported the TiO2 /β-Cyclodextrin hybrid structure of organic–inorganic nanomaterials with efficient photocatalytic water splitting prepared with single-step strategy. This hybrid material demonstrated excellent HER of 5800 μmol h−1 after 8 h without involving noble metal and recyclability with almost same yield for three successive runs. The alveolate structure of the hybrid catalyst acts as a channel to trap more light and electrons, it also provides large surface area for photocatalytic reaction [16]. Yang el al. invented a photocatalysis system that generated electricity from atmospheric water by using Cu2 O @BaTiO3 hybrid nanoparticles. A hydrogel form of this hybrid catalyst splits 36.5 mg of water by 150 mg hydrogel and generates photocurrent of 224.3 μA cm−2 under 10 mW cm−2 illumination [17]. Su et al. investigated separate hydrogen and oxygen evolution technology using wireless and redox mediator-free Z-scheme twin reactor separated by Nafion membrane. The performance of the system was accessed with CuFeO2 and Bi2 TiO3 which acts as hydrogen and oxygen evolution photocatalyst respectively. Reduced graphene oxide was used for water splitting under light irradiation and copper wire to improve the electron collection from rGO. The work is claimed

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to be significant as it evades explosion potential, hydrogen separation cost, and minimized the resistance loss from wiring and mediator cost [18]. Though these literatures evidenced the effort toward future hybrid system, more focused efforts are required to increase the rate of hydrogen generation and to reduce the higher input energy cost and engineered solution to uplift the successful laboratory-scale system to pilot scale and making the application of solar fuels more meaningful. In this pursuit, approaches for solar hydrogen generation developed/investigated by our group are as follows: Development of photocatalytic materials Catalysts that are durable, efficient and perform under the harsh conditions of sunlight are the prime requirement to make solar fuels a reality. In this context, the field of plasmonic materials in solar energy utilization (SUN) is expected to lead to significant improvements in conventional systems and also in unique applications. Thus, development of highly performing selective photocatalysts and plasmonic materials would facilitate development of more efficient devices and system for solar fuels (in specific hydrogen) in all types of photo hydrogen generation system viz. photothermal, photothermoelectric, photovoltaic and photocatalytic platforms. In pursuit of this, our group has developed bimetallic Au-Pt, Cu-Pt and Ag-Pt titania composites that are tested for photocatalytic water splitting reaction showing exemplary HER ranging from 12 mmol/h/400 mL to 17 mmol/h/400 mL in presence of donor including methanol, ethanol, glycerol and acetic acid in laboratory—a unique mechanism of in-situ generated low-cost Cl– -based donor postulated [19]. Donor-assisted pilot-scale photocatalytic hydrogen generation system Technical glitches in scale up and higher energy input cost are the two major hurdles suppressed the growth of conventional laboratory-scale photocatalytic hydrogen system. Illumination lamp requires higher input energy. To overcome the issue, our group has developed 30 Ltr capacity pilot-scale photocatalytic reactor which is the first of its kind of unique facility capable to produce hydrogen at very high rate. The issue of higher input energy/electricity is resolved by operating the whole system on renewable energy generated through PV panels installed on the rooftop of the housing of photocatalytic reactor system. By considering all crucial parameters, this photocatalytic reactor system operated successfully for hydrogen production using Au-Pt photocatalyst and methanol as donor which delivered the promising HER of 380 mmol/h in UV–Visible illumination. Another factor contributing to a significant enhancement in HER is attributed to the presence of donors and the in-situ generation of Cl ion [19]. Efforts are being made to harvest the UV and IR of the PV panels to generate hydrogen and also the heat of the UV lamp is being exploited for water splitting through use of pyro electricity.

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3 Electrochemical or Photoelectrochemical Water Splitting Water electrolysis, also referred as electrochemical, is a promising method, where an external electric current is applied to decompose the water into hydrogen and oxygen. In the process, current passes through an electrochemical cell leaving H+ ion flowing to the −ve electrode (cathode) and OH− ion to the +ve electrode (anode), and producing hydrogen and oxygen on these electrodes respectively. These two half cells or electrodes can be separated by proton exchange membrane (PEM), to permeate only the newly formed proton to cathode electrode thus higher proton conductivity, lower gas exchange and compact design to operate under higher pressure. The process of a photoelectrochemical cell is almost similar to that of an electrochemical cell, with the key difference being that it uses light energy to convert into electricity within a cell involving two electrodes, immersed in an aqueous electrolytic solution, of which at least one is made of semiconducting material to absorb the light. This electricity then used for splitting of water into hydrogen and oxygen, which may reduce external energy consumption partially or fully depending on the efficiency and nature of semiconducting materials. Due to slower kinetics and higher thermodynamic requirement, the conventional water splitting electrolyte generally requires higher input voltage from 1.8 to 2.5 V. Although PEC technology is at very good transition phase with several improvement in terms of coupling with conventional solar cell, perovskite solar cells and dye sensitized solar cell [20], there is still scope to improve the issues of lower efficiency, durability and higher cost to make product market viable and for large-scale commercial operation. In particular, contemporary and synergistic efforts with focus on hybrid technologies are required for the development of low-cost and high-throughput nanomaterials. It includes (i) enhancement in sunlight absorption (ii) tailoring the potential material singly or in mixed oxide form (iii) surface catalysis engineering (iv) improvement in stability, durability and lifetimes of the materials (v) reduced consumption of materials and processing costs (vi) exploring the hybrid technologies to provide instant renewable energy solution (vii) band gap energy (viii) electrolyte temperature. To address this issue, researchers across different continent have taken keen interests and published several literatures on the topic. Wang et al., investigated the two complexes [Co(bpy)2 (SCN)2 ]1 and [Ni(bpy)2 (SCN)2 ]2 with bipyridine ligands that exhibit good catalytic activity for both electrochemical and photoelectro chemical hydrogen evolution [21]. Li et al. presented the decoupled water electrolyzer design for water splitting hydrogen generation with great flexibility and safety to restrict the mixing of hydrogen and oxygen. Two inexpensive iron complexes are introduced for this purpose as protonindependent electron reservoirs to restrict the corrosive environment and to improve the efficiency of electrocatalyst for oxygen evolution reaction. The process requires comparatively smaller voltage than direct water splitting and provides pure hydrogen. The work has achieved 100% Faradic efficiency and remarkable cycling stability for electron reservoir [22] (Fig. 2).

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Fig. 2 Photoelectrochemical cell operated on sunlight

However, among all in-vogue approaches, only photovoltaic (PV)-based or coupled water electrolysis is reasonably mature and has the potential to significantly make a mark in the current energy needs and scenario considering the scale of infrastructure already installed for the promising solar to hydrogen pathways. In this context, our group has conducted research on solar PV-based water electrolysis essentially including solar PV for electricity and water electrolyzer for generating hydrogen. Solar PV-based water electrolysis (PV-WE) Efforts are being made to reduce the cost of hydrogen by reducing the CAPEX and OPEX of solar PV-based water electrolysis. Design and patent protected functional PV panel (FPV) has been developed (patent and design registration grant pending) for skillful photons, thermal and biofilm management which prevent voltage decay & improve shelf life with overall enhancement efficiency of FPV to 22% vis-à-vis 18% for Commercial PV. Similarly facilitated water electrolyzer (patent grant pending) has been developed in our laboratory with emphasis to reduce investment/operation cost and provide high throughput. The initiatives undertaken for this purpose include—(i) development of low-cost Pt-free electrodes (ii) development of high-throughput new sacrificial and non-sacrificial donor-assisted system for spatial separation of HER and OER and for reducing electricity requirement in conventional WE. The FPV has been coupled with facilitated water electrolysis system for designing compact and modular integrated FPV-based PV-WE system with promising HER to retrofit it with 300 W fuel cell.

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4 Photothermal Water Splitting The solar cell-driven water splitting is typically energy-driven water splitting strategy. The conventional semiconductor-based solar energy conversion technology and material is not tailored for the capturing infrared (IR) light; thus, utilization of full solar spectrum using established material is relatively low. Most of the existing photocatalytic materials and solar cell are effective only in the ultraviolet and visible light range. Since IR constitutes 50% of solar spectrum, there is ample scope to develop catalytic material active in entire solar spectrum. However, the concept requires lot of research to find or fabricate the correct material singly or in combination. At this juncture, the synergized thermoelectric device and infrared active materials supplies are only choice to enhance the utilization of full solar energy. The process has wide array of scope in industrial boilers and power plants where wasted hightemperature water is an inevitable, that can be used for photothermal catalytic water splitting to produce solar fuel and high-temperature heat to achieve solar energy cascade utilization [23]. The thermal catalytic system has also wide scope to couple with the existing photocatalytic and photoelectrochemical infrastructure. Several researchers reported thermal-driven water splitting hydrogen. Thus, water splitting driven by thermoelectric is extensively conducted by our group. Recently Zhang et al., studied the Cu-modified TiO2 for overall photothermal catalytic water splitting, the yield is reported ten times higher than the gas–solid interface at same reaction temperature due to reduced energy barrier of rate determining step and reduced charge-transfer resistance, that also explain the positive correlation between the hydrogen yield and temperature [23]. Ai et al. presented the photothermally boosted electrocatalytic water splitting by using broadband solar harvesting with nickel phosphide (Ni2P) within a quasi-Ni-BDC-MOF. The use of thermal energy reduces the activation energy barriers and accelerates kinetics to provide higher rate to electrocatalytic water splitting. Moreover, the photothermally active material pushes the much-needed surface heat localization to satisfy the integration of in-situ heating to supply an excess energy to promote electrocatalytic reaction. By using above catalyst, it demonstrates ultralow overpotential of 246 and 218 mV to deliver 100 mA cm−2 current density for HER and MER [24]. Zhao et al. constructed PANI/ BiVO4 composite photoanodes for photothermal effect-enhanced photoelectrochemical water splitting. Bulk charge separation was improved due to formation of p-n heterojunction. PANI is incorporated to enhance the dual function of whole transport and photothermal conversion. Further, the addition of co-catalyst cobalt phosphate accelerated the surface oxidation reaction to promote the photothermal effect of PANI. In presence of NIR light, this catalyst Co-Pi/PANI/BiVO4 photoanode achieves significant water oxidation photocurrent 4.05 mA cm−2 at 1.23 VRHE , over 300% higher than that of pristine BiVO4 photoanode [25]. The work paved way to improve the performance of other photoelectrodes viz. Fe2 O3 , TiO2 and WO3 . Guo et al., developed multi-functional Pt/ZnIn2 S4 catalyst for photothermocatalytic water splitting hydrogen production under full solar spectrum. The enhanced photothermal effect due to IR radiations and plasmon thermal effect increased temperature to 45 °C

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and generated photothermal effect, accelerated charge separation, transfer and redox reactions. The work is so significant that reporting HER 19.4 mmol/g/h over this catalyst which is almost double than conventional photocatalytic process [26]. All of these reports, obviously proved the benefit of photothermal effect. In this context, the following approaches are undertaken in our laboratory which include Hybrid photothermal pure WS and donor-assisted hydrogen generation Although several literatures reported the benefit of hybrid system, conducting the experiments in real sun is still challenging attributed to the several factors viz. weather uncertainty, poor efficiency, fluctuated solar intensity, higher temperature and pressure in packed system, lack of technology to control the illumination, probable leakages. To address some of the issue, experiments were conducted in donor-assisted 3 Ltr capacity photothermal cum photocatalytic flat reactor system in natural sunlight of 10 sun conditions. The temperature measured was 80–90 °C. This flat reactor system using Au-Pt-TiO2 composites catalyst and ethanol as donor delivered HER in the range of 250 to 800 ml/h which is exemplary and not reported so far. Oxidative hydrolysis of nano zinc showed HER of 1145 μmol/h compared to 300 μmol/h for micron-sized zinc (recovery through electro deposition shows promising results) [27]. The glimpses of this work and information will pave way to carry such kind of work in natural sunlight. Enzyme-triggered photocatalytic hydrogen generation Carbonic Anhydrase (CA) Enzyme-based photocatalytic hydrogen has attempted in our lab and very encouraging results have been obtained and published with HER of 1238 μmol/h in presence of CO2 as donor [28].

5 Conclusion Most promising approaches for green hydrogen rely on solar light-triggered processes for the conversion of water into hydrogen. Although solar to hydrogen technologies including thermal, photothermal, photocatalytic, photoelectrochemical and electrochemical are showing promising leads for hydrogen generation, concerted efforts are still being made across the globe to make green hydrogen based on solar energy system commercially viable. This challenging task may be addressed by deploying combination of approaches like electrochemical and photoelectrochemical, photocatalysis and enzymatic etc. to address issues of spatial separation of hydrogen and oxygen, kinetics etc. Efforts are also required to find a material singly or in combination to cover the entire natural solar spectrum. In this context, glimpses of our work on hybrid approaches for solar hydrogen generation have been provided.

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Acknowledgements Financial support from Department of Science and Technology (DST), India under the grant GAP-2536 and Chemsolar project of TAPSUN programme of CSIR is acknowledged.

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Potential for H2 Generation Using 2D-g-C3N4 Nano-Photocatalysts A. Nazeer, F. Ahmad, and S. Ahmad

Abstract The discovery of graphene nanosheets (NSs) opened a flood gate of activities for studying graphene and graphene like hexagonal lattices. Particularly, the photoelectronic properties of these 2D-layered materials are of significance as they can be modified by changing their atomic arrangements. The zero-band gap of graphene did not in principle favour for switching applications against silicon. In contrast, graphitic carbon nitride (GCN), closely resembling graphene, exhibits semiconducting behaviour with excellent photoelectronic properties. GCN could photocatalytically produce H2 by water splitting in the presence of solar radiation. Extensive theoretical and experimental studies are currently going on to convert it not only into quantum dots (QDs) and nanotubes (NTs), but also to conjugate with other 2D-NSs. The introduction of lattice defects during doping and heterojunction formation in combination with other 2D nanomaterials turned out useful in influencing photogenerated charge carrier recombination and subsequent transport properties enabling them to participate in redox reaction at the surface. This entire process of photocatalytic effect in ideal monolayer of GCN-NS involving intermediate steps like photogeneration of electrons and holes, exciton formation, charge carrier separation, and subsequent participation in redox reaction, to generate hydrogen from splitting water, has theoretically been simulated using DFT models to understand the details at different timescales and spatial resolutions. The experimental side of developing GCN-NSs based photocatalysts has not been without challenges. This chapter describes about the salient progress made in preparing GCN-NS-based photocatalyst for H2 generation available from the current publications. It is still too early to say that these photocatalysts would be crossing the viability barrier of 10% for their large-scale applications in meeting the global green energy alternative in place of fossil fuels and reaching the zero pollution.

A. Nazeer · F. Ahmad · S. Ahmad (B) 508, BWT, Eros Garden, Charm wood Village, Faridabad, Haryana 121009, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Goel and G. Sen (eds.), Climate Action and Hydrogen Economy, Green Energy and Technology, https://doi.org/10.1007/978-981-99-6237-2_9

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Learning objectives: • • • •

GCN as a photocatalyst Redox reaction on the surface of two-dimensional (2D) nanostructures Photocatalytic H2 generation from water Molecular engineering for novel syntheses of 2D materials

Keywords Graphitic carbon nitride · Photocatalysis · Water splitting · Solar photovoltaic cells · Redox reaction · Hydrogen as green energy

Abbreviations GCN b-GCN GCN-NSs CB CDs C6 N7 C3 N3 DFT HOMO GCN-QDs GCN LUMO MCS NMs NH4 Cl PCE TiO2 TD-DFT

G-C3 N4 Bulk g-C3 N4 G-C3 N4 Nanosheets Conduction Band Carbon Dots Tri-s-triazine S-triazine Density Functional Theory Highest Occupied Molecular Orbital Graphitic Carbon Nitride Quantum Dots Graphitic Carbon Nitride Lowest Unoccupied Molecular Orbital Mesoporous Carbon Spheres Nanomaterials Ammonium Chloride Power Conversion Efficiency Titanium Dioxide Time-Dependent Density Functional Theory

1 Introduction GCN-NSs with tunable optoelectronic properties are finding growing applications in different fields including photocatalysis, sensing, and photovoltaics with green environmental impacts. GCN-based photocatalytic degradation offers the feasibility of environmental pollution remediations using optical radiation and photocatalytic interactions. Similarly, in photovoltaics, ~2.7 eV of energy band gap facilitates

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absorption over a wider spectrum of solar radiation resulting in increased photogeneration of electrons and holes. With higher sensitivity and selectivity, higher surface to volume ratios, and chemical stability, GCN-based materials have advantages in realizing nanosensors. These salient features of GCN have been discussed at length in the cited references. A brief description of physicochemical properties of GCN-NSs compared to those of the other C-based nanostructured materials reveals the clear differences in their optoelectronic properties and hydrophilicity. For instance, GCN is more hydrophilic and photoactive in visible light, whereas others are hydrophobic and non-reactive as reviewed elsewhere. GCN-NS family of nanomaterials (NMs) employ either triazine or heptazine-based C-rings. The synthesis of GCN primarily deploys the pyrolysis of its precursors in chemical vapour deposition, templating, and doping, as used in the synthesis of the other CNMs [16]. Despite using different synthesis protocols of GCN-NSs, the bulk-GCN (b-GCN) is invariably pyrolyzed using several N-containing precursors. However, b-GCN exhibits poor electronic conduction due to shorter lifetime of the photogenerated charge carriers. Structural defects not only lower the quantum yield but also affect the photogenerated charge carrier recombination adversely. However, employing different techniques of exfoliation to prepare single/multiple NSs possessing larger specific surface areas (SSA) for surface reactions causing reduced recombination and diffusion length of photogenerated charge carriers—all add up to improve the electronic conduction as discussed in the cited references [12, 16, 18, 40, 53]. Exfoliation techniques employing liquid, thermal etching, ultrasonic agitations, and chemical blowing produce few-layered GCN-NSs. However, it has been reported that for efficiently exfoliating the b-GCN into NSs, there are still several issues to resolve before realizing better yield of controlled morphology, for which it still needs deeper understanding. Once b-GCN is transformed into lamellar NSs, it is possible to transform them into different morphologies, such as quantum dots (QDs), and nanorods/nanotubes (NRs/ NTs) possessing better features. GCN-NTs have been synthesized using hard-, soft, and self-templating methods. QDs are synthesized by hydrothermal processing. Recently, honeycomb structure of GCN-NSs was reported using a salt-template technique discussed elsewhere. Alternate method of enhancing the optoelectronic properties of GCN-NSs employs heterojunctions in combination with other CNMs and introducing structural defects. GCN-NSs have also been used in preparing 0/2D, 1D/2D, and 2D/2D heterojunctions. The current trend is to prepare 0D/2D composites with enhanced photocatalytic properties besides preparing other 2D/2D interfaces comprising GCNNSs with other 2D-NMs for controlling their electronic properties. Over time, the realization of heterojunctions such as type II, Schottky, and Z-schemes has been recognized for its ability to enhance photo-driven reactions. This enhancement stems from the reduction in the diffusion length of charge carriers and their recombination rates. Heat treatment of intrinsic b-GCN generates structural defects that are known to amplify its photocatalytic activity. Using this concept, the hetero-atom doping using elements like N, B, Bi, and P has been observed to exert a significant influence

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on the photoelectronic properties of GCN. This phenomenon has been extensively discussed in many cited publications [2, 4, 13, 14, 15, 17, 20, 22, 35, 38, 47]. Most of the investigations conducted thus far have revolved around assessing the photocatalytic characteristics of GCN, after its initial deployment as a visible light photocatalyst for water splitting to produce H2 . Furthermore, the incorporation of GCN-NPs within the active layer of bulk heterojunction polymer solar cells yielded promising outcomes, notably augmenting the power conversion efficiency (PCE) of said solar cells. It is noteworthy that while GCN exhibits restricted electronic conductivity, its utilization within polymer solar cells has yet to reach its full potential. The prospect of introducing tailored modifications to the polymeric matrix remains open for future exploration, thereby offering avenues to enhance GCN’s performance in this domain. GCN, with unable energy band gap, offers promising applications including photovoltaics, sensors, and photocatalysts. An effort has been made here to highlight the salient progress made in synthesizing and modifying the basic GCN-NM described below in section A. Besides, the study of the photocatalytic features of GCN has also been studied via numerous computational schemes as described in section B. Part A

2 Experimentally Measured Physicochemical Properties Experimentally observed photocatalytic properties of GCN-NSs are already reported in the current research publications. A brief overview of these findings is summarized below to highlight their emerging applications explored by various research groups.

2.1 Atomic Arrangements The polymerization of N-containing precursors like melamine producing the polymeric-GCN (p-GCN) was first reported in the early nineteenth century, and since then, much progress has been made in developing different protocols to control the relevant structure-specific reactivity features. The internal structure of p-GCN involves C6 N7 and C3 N3 rings in which C3 N3 − based lattice is more stable under ambient conditions. Theoretically, SSA of a monolayer of GCN could as be high as 2500 m2 /g. The GCN-NSs, closely resembling to graphene, have π -conjugated planes comprising sp2 -hybridized carbon and nitrogen atoms. The structure of as-prepared GCN exhibits a configuration with two successive misaligned C3 N3 -based layers of A-B type. This misalignment takes care of the repulsive forces of π -electrons in adjacent layers as discussed in the cited references [48, 49, 55, 56].

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The interaction of the lone-pair electron state of nitrogen (N) and the π-bonding facilitate stabilizing the resultant position of the lone-pair electron. This, in turn, governs the electronic configuration of n-type GCN. Computational simulations illustrate the formation of the valence and conduction bands using Pz orbitals from nitrogen and carbon atoms. Therefore, both C and N atoms serve as active sites for redox reactions. The GCN photocatalyst additionally facilitates the effective separation of photogenerated electrons and holes. With a band gap measuring 2.7 eV, GCN exhibits broad sunlight absorption and makes it suitable for applications in water purification, hydrogen (H2 ) generation, and solar cell technology, as reported [39].

2.2 Chemical Syntheses The pyrolysis of N-rich precursors like melamine, dicyandiamide, thiourea, and urea produces a b-GCN with energy band gap of 2.7 eV. However, it suffers from low SSA due to stacking of the individual lamellar sheets produced during polycondensation. GCN also suffers from poor QE due to limited or no electronic transition and faster recombination of photogenerated electrons and holes. To circumvent these drawbacks, attempts have been made to exfoliate the b-GCN into individual single and multiple NSs that have been used in preparing nanotubes (NTs) and quantum dots (QDs). Moreover, hetero-atom doping with other elements or combining GCN with other 2D-NMs provides better opportunity to form nanocomposites as discussed by several groups in the recent past [6, 10, 32]. Planar layers of N and C atoms in GCN-NSs are held together by strong in-plane covalent bonds and out of plane inter-layer weak bond formed by van der Waals forces holding the monolayers together in b-GCN. These layers can be separated into 2DNSs when adequate energy is applied to break the inter-layer forces of attraction in a suitable solvent. Liquid phase exfoliated GCN-NSs from b-GCN exhibit 2.65 eV energy band gap. Thermally exfoliated GCN-NSs of b-GCN exhibit a larger band gap of ~2.9 eV. Higher SSA of ~306 m2 /g and improved electron transport properties as compared to those in the b-GCN due to better quantum confinement [40]. The exfoliation of individual/few-layered NSs has been feasible using chemical, thermal, ultrasonic, and chemical blowing in separating them as reported elsewhere [8, 43, 45]. Concentrated H2 SO4 , HNO3 , and HCl acids have been used in chemical exfoliation of b-GCN into mono or few-layered NSs. Thermal decomposition of dicyandiamide at 500 ° C-based preparation of b-GCN when mixed with concentrated H2 SO4 and H2 O produces the NSs after sonication. Ideally, in the sonication process, concentrated H2 SO4 intercalates into the inter-layer spaces in b-GCN, and heat produced there breaks the inter-layer forces of attraction. Further application of ultrasonic energy helps in delaminating the b-GCN into mono/multilayer NSs. Concentrated HNO3 and HCl-based exfoliations have comparable yields (40 and 41%) and similar performance in photoreduction.

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It is found that the exfoliation process is dependent on the concentration of H2 SO4 . At low concentration, b-GCN is exfoliated to a lesser extent producing only fewlayered NSs. HNO3 added to b-GCN + H2 O and sonicated produces few-layered GCN-NSs with SSA of 179.5 m2 /g compared to 17.4 m2 /g of b-GCN. The superiority NSs over b-GCN have been evident in their enhanced performance in photodegradation and water splitting processes, as documented by Rono et al. [40]. Despite the exfoliation approach leading to NSs with enhanced SSA, it is characterized by drawbacks such as lower yield, limited controllability, time-consuming processing, and the utilization of corrosive chemicals. Consequently, these factors render this exfoliation strategy less preferred. Subjecting b-GCN to heat treatment helps in disrupting the weak inter-layer forces of attraction, thereby causing exfoliation to occur. This transformation also produces porous GCN-NSs. When b-GCN is thermally etched at 500 °C for a duration of 2 h in an air environment, the resultant samples display SSA of 216.3 in contrast to 95.5 m2 /g of the chemically etched NSs. Recently, GCN-NSs derived from the thermal etching of melamine were used to prepare a 2D nanocomposite of WO3 /GCN demonstrating enhanced photocatalytic activity in the conversion of water into hydrogen. Despite the advantages of the exfoliation protocol being cost effective, solvent-free, time efficient, and yielding a substantial number of beneficial defects, it does show some limitations. Notably, it produced lower crystallinity with a comparatively higher SSA, as highlighted in the pertinent publications [3, 9, 41]. GCN + MoS2 composites were reported involving b-GCN prepared from thermal decomposition of urea followed by dispersion in N-methyl pyrrolidone before subjecting to ultrasonication to exfoliate the NSs for photocatalytic H2 generation. The liquid exfoliation of b-GCN in water is green processes, where NSs of higher SSAs and relatively higher crystallinity are formed, which are very critical for photodriven reactions. However, the demerits of this method might include tedious operations including sonication, long preparation cycles, higher cost, and lower yields [43, 45, 53]. An alternative method involves incorporating blowing agents like NH4 Cl and MgCO3 into the process, which release gases during the heat treatment stage. The gas emitted within the layered structure of b-GCN induces exfoliation, resulting in the formation of flake-like porous GCN-NSs. This chemical blowing approach has been shown to yield GCN-NSs with improved photocatalytic activity. In this process, a combination of melamine and MgCO3 is subjected to heat treatment to decompose and generate CO2 gas, which aids in the separation of the nanosheets from the parent b-GCN structure. More recently, Z-type heterojunctions were prepared by combining BiOBr, CDs, and GCN as constituents. For this composite, the GCN-NSs were produced using a chemical blowing protocol by heating a mixture of melamine and ammonium chloride. In this process, NH4 Cl was a blowing agent, while melamine served as precursor b-GCN. This strategy offers a streamlined single-step process, which not only saves time but also mitigates the agglomeration of nanosheets. The resulting porous structures had increased number of reaction sites resulting in enhanced overall reactivity.

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Nonetheless, a significant challenge lies in this approach to choose a suitable blowing agent. The chosen agent must not adversely affect the optoelectronic properties of the ensuing nanosheets. This challenge was further examined and discussed in several pertinent publications (Zhang3 et al. 2019) [42, 50, 52, 55, 56]. GCN-NTs demonstrate distinctive attributes of higher absorption of visible light, a substantial SSA, swift electron transportation, and diminished recombination rates of photogenerated charge carriers. The fabrication of GCN-NTs employs techniques encompassing hard, soft, and self-templating methodologies. In the hard-templating approach, mesoporous GCN is synthesized utilizing CaCO3 as a template, which is subsequently dissolved in HCl. The resulting mesoporous GCN-NTs exhibit a SSA of 38.6 m2 /g and manifest a nearly fourfold increase in photocurrent compared to b-GCN (Rono et al. 2021). Conversely, the soft-templating strategy involves melamine precursor and Pluronic P123 surfactant to generate porous GCN, exhibiting SSA of 90 m2 /g, and displays augmented photocatalytic hydrogen (H2 ) production [22, 23, 33, 34]. An innovative self-templating protocol, melamine precursor, was used for the first time to craft GCN-NTs. By subjecting both unaltered and transformed components of melamine to pyrolysis, synthesis of GCN-NTs was achieved yielding specimens enriched with a higher concentration of nitrogen defects. Another scheme of thermal etching of urea was used to synthesize b-GCN for producing nanosheets, nanoribbons, and quantum dots. The initial b-GCN was subjected to heating to create GCN-NSs, which were subsequently treated with acid to produce nanoribbons (NRs). These NRs were then further subjected to hydrothermal cutting, resulting in the formation of quantum dots (QDs). These advancements were detailed in research works of Liu et al. [30] and Mo1,2 et al. [33, 34]. One dimensional rod-like GCN-structures are attracting attentions because of their high surface area to volume ratio providing more reaction sites. To improve the SSA of mesoporous carbon spheres (MCS), a composite of GCN-NWs impregnated in MPCs was reported to form a bulk composite structure with increased SSA with improved electrochemical properties than graphene, CNTs, and activated carbon materials for preparing double-layer capacitors. More recently, a composite consisting of GCN-NWs substrate for conducting poly(3,4-ethylenedioxythiophene): poly (4styrenesulfonate) (PEDOT: PSS) showed good capacitive properties with recycling flexibility as reported in the cited references [36]. GCN-QDs are being examined due to their chemical stability, bright fluorescence, large specific surface area, biocompatibility, and moderate band gap. GCN-QDs are synthesized by heating the melamine precursor at 550 ° C followed by etching in a mixture of concentrated H2 SO4 and HNO3 as reported [29]. Despite significant progress made so far in preparing GCN photocatalyst, several drawbacks including high recombination rates of charge carriers, low SSA, and poor light absorption capabilities are still there to take care. For this, a macroporous 3D-GCN was synthesized using melamine sponge followed by one-step polymerization in urea. The resultant product was cut into different 3D shapes of GCN. Basically, melamine and urea are precursors of GCN, and this method produces a macroscopic 3D-GCN with enhanced photocatalytic H2 production. A mesoporous

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3D-GCN was reported using silica template after optimizing the self-polymerization reaction conditions. The subsequent 3D-GCN was 6.5 × times superior to b-GCN when used in photocatalytic H2 evolution. This 3D architecture offers more sites for the photoreaction to take place with improved light absorption. Similarly, 3DGCN was synthesized with 30 times more efficacy of photocatalytic H2 evolution compared to pristine GCN. High-temperature treatment of acid treated and untreated b-GCN samples together produces porous GCN with enhanced SSA and improved light absorption characteristics [7, 31].

2.3 Catalytic Efficiency The phenomena of doping of layered GCN create cavities to accommodate heteroatoms that upshift the conduction band edge without affecting the optical absorption. Such alteration in the structure enhances the electronic and optical properties. For instance, thermolysis of melamine and organophosphoric acid, without any template, produced a flower-like structure with improved capability of H2 production from water split. P-doped flower-like GCN with a large SSA and many active sites improved its optoelectronic properties significantly. Another P-doped mesoporous flower-like GCN was used in photocatalytic splitting of H2 O. The presence of P atoms slows down the recombination rate of photogenerated electrons and holes and thus enhances the catalytic efficiency as reported [51]. Preparing GCN-NS-heterojunction alleviated the problems of low photoabsorption poor charge carrier separation. Different heterojunctions attempted so far include Z-type, type II, and Schottky type as described by several groups [22, 23, 25, 37]. Combining sulphur-mediated GCN-NSs and pristine ones in a type II heterojunction with appropriate band alignment facilitates better charge carrier transfer which ends up in improved photocatalytic H2 production as reported [21, 24, 26, 27, 28]. Deliberately introduced defects facilitate altering both structural and electronic properties of GCN-NS. For instance, controlled heat treatment b-GCN introduces significant number of defects that help in improving the phenomenon of photocatalytic hydrogen evolution. These defects facilitate partial break-up of inter-layer forces of attraction resulting in the formation of porous structures that changes the electronic structure and charge transfer efficiency. The porous NSs exhibit extended light absorption and enhanced photocatalytic performance, particularly in the context of H2 evolution. Another method of modifying GCN was reported using heat treatment of a mixture of dicyandiamide and NH4 Cl resulted in significant structural alterations, specially creating a greater number of active sites on the material surface for redox reactions. This process could significantly enhance the photocatalytic efficiency of H2 evolution. The changes in both electronic band structure and surface morphology contribute to improved photocatalytic properties, demonstrating the importance of a synergistic effect between structural defects and electronic structure modifications.

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Calcination of a mixture of NaCl and dicyandiamide was reported to manipulate the morphology and electronic band structure of GCN ending up in forming a honeycomb-like structure. This tailored structure exhibited enhanced photocatalytic H2 evolution. The synergy between the alterations of material’s morphology and electronic band structure could significantly improve overall photocatalytic activity as reported by Zhang et al. [54] and Guruge et al. [11].

2.4 Green Photocatalysis GCN has been used in diverse applications due to its unique characteristic properties. Electron-rich GCN material with tunable band gap is emerging as an excellent non-metallic photocatalyst particularly for water splitting to produce hydrogen or degrade the pollutants. For the enhanced properties using defect engineering and lattice modifications, it is emerging as a superior photocatalyst. H2 evolution from splitting of H2 O is an attractive way to solve the problems of energy shortages and environmental pollutions. Theoretically, the valence and conduction bands of GCN are in the proper position to photo-reduce water to produce H2 and O2 . However, the photocatalytic decomposition of water under visible light is still difficult. This is because the O-producing reaction is a four-electron process, which is more difficult than that of H2 -producing reaction. However, the photocatalytic efficacy of pure GCN is not high, so it needs to be improved, including the preparation of porous GCN, elemental and molecular doping, composite carbon materials, and so on. It should be noted that the photocatalytic H2 production using GCN requires coupling with metal catalysts like Pt, Au, Ag, and similar others as well as non-precious metal like NiS, NiS2 , MoS2 , WC, and similar others [5]. GCN’s ability to absorb light over a wide range of the solar spectrum, combined with its electron-rich nature, makes it an attractive material for photovoltaic applications by incorporating it in some hybrid or composite forms in solar cells. Water splitting for H2 generation is emerging as an alternative technology of hydrogen fuel production as discussed more in this chapter. GCN’s photocatalytic features have been deployed in environmental remediation involving degradation of organic pollutants in water and air. Unique surface properties and electronic structure of GCN-NSs can influence reaction pathways, enabling more efficient and selective catalysis. Since the successful exfoliation of black phosphorous (BP) in 2014, it is gaining importance as an attractive photocatalyst. Analogous to g-C3 N4 , the BP has a tunable band gap, high SAA, better optoelectronic properties, and is metal free. In contrast, BP has a band gap between 0.3 and 1.5 eV thus absorbing more visible light than GCN with 2.7 eV band gap. To capitalize on a synergism, efforts were made to engineer a 0D-2D (BPQD/GCN) nanocomposite, which exhibited remarkable photocatalytic hydrogen production. Similarly, C-doped ZrO2 /GCN/Ni2 P composite material also generated H2 from water splitting. Another report came using tungsten trioxide/

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graphitic and GCN nanocomposite (WO3 /GCN-NSs) that was deployed in photocatalytic production of H2 with 400 lmol/hg compared to that of pristine GCN-NSs exhibiting 27 lmol/hg. Another GCN/Ag3 PO4 nanocomposite exhibited enhanced photocatalytic splitting of water as well as degradation of pollutants possibly because of increased dispersion of NMs, improved optical properties, and low recombination rate of holes and electrons. Part B

3 Ab Initio Studies Computational simulations have been extremely useful in estimating the associated physicochemical properties of various 2D-NMs including GCN. The simulation of GCN is, however, still inadequate and asks for further research. Theoretical DFT calculations determine electronic properties like band gap energy and electron transport properties across the interfaces for given crystalline structure. Alternately, quantum simulation offers better system description but is applicable only in small systems with limited degrees of freedom and especially not in solution phases. Spectroscopic observations along with ab initio calculations of GCN have confirmed the dependence of energy band gap on the lattice constants, stacking of the lamellar sheets, and the stress generated during processing (distortions) that may impart large variations in the conduction band edge, while the valence band experiences only smaller shifts decided by the structural geometry as reported in the cited references [1, 45]. The calculated band gap of non-planar corrugated structure of triazine-based GCN falling in the range of 1.6–2.0 eV matches well with the measured band gaps. The experimentally measured optical band gap of as-prepared GCN samples matched with the band gap of most stable phase of GCN calculated as 2.87 eV. Theoretical simulations indicated that perhaps during polycondensation at different temperatures promoted dissimilar phases of GCN to coexist. Most stable phase exhibiting a direct band gap of 2.87 eV is found very close to the experimental value. Such results also confirmed the correlations between temperature and band gap as increasing temperature increases the proportion of material undergoing phase transformation. A hybrid functional-based theoretical calculation of the band gaps of GCN nanoribbons of 1.61, 2.23, and 2.84 nm widths showed the corresponding band gaps of 3.06, 2.73, and 2.71 eV, respectively. This revealed that increasing widths from 1.61 nm to 2.84 nm, the corresponding band gap energies reduce from 3.06 eV to 2.71 eV. This trend in the band gap reduction can be assigned to improving the crystallinity of GCN nanoribbons with improved degree of polymerization. This is consistent with the behaviour of p-GCN exhibiting a red shift at higher polycondensation temperatures.

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The optical properties of molecular p-GCN were found strongly dependent on the structure and processing temperature. The GCN-NSs, nanoribbons, and QDs exhibit larger SSAs resulting in shorter diffusion lengths of the charge carriers possessing enhanced photocatalytic properties. Realization of electrochemical photolysis of water at a TiO2 electrode reported in 1972 promoted the development of photocatalysts like TiO2 , CdS, ZnO, ZnS, and GCN. Unfortunately, these photocatalysts in their pristine (undecorated) forms showed poor photocatalytic performances. Further studies were therefore dedicated to developing either novel photocatalyst or modifying the existing ones via controlled synthesis, elemental doping, and formation of hybrid materials as reported [57]. DFT simulations are extremely useful in the search of optimal photocatalyst material designs out of very large number of possible options. It also provides sufficient help in interpreting the experimental by taking into the influences of atoms, molecules, and unit cells. More specifically, DFT helps to assess the effect of elemental doping in the regular lattice geometries of photocatalysts, the interaction between different components in the composites, the adsorption of molecules, and photocatalytic reaction processes onto the surface of photocatalysts. DFT investigations of the traditional photocatalysts including TiO2 , CdS, ZnO, and ZnS are quite mature, while that of GCN-NSs is in infancy. GCN-NSs are relatively nascent photocatalysts for H2 generation since 2009. Out of the two accepted crystal structures, namely tri-s-triazine- and s-triazine-based lattices, it is difficult to identify experimentally which one is there in a real GCN sample. Although, both these structures are widely used in experimental and theoretical studies reported [57]. DFT calculated band gaps are model dependent. A monolayer of GCN-NS shows a larger band gap than that of b-GCN and is due to quantum confinement. The indirect bandgap of b-GCN changes to direct in a monolayer of GCN-NS. The valence band of GCN-NS is formed out of the orbitals of N atoms, and its conduction band involves the orbitals of C and N atoms. Correspondingly, its highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are distributed on N atoms and on C and N atoms, respectively. The work function of GCN is estimated around 4.50 eV and is weakly correlated with the number of layers [57]. Numerous possibilities of modifying the energy band gap to control the nature of charge carrier recombination and transport properties leading to charge separation have been explored extensively and reported recently. Some of these observations arrived at in ab initio simulations are briefly highlighted for their experimental relevance. Co-doping involves introducing multiple dopant elements into a material to modify its electronic properties. Multi-elemental co-doping refers to incorporating two or more different dopant elements into the GCN lattice to enhance the catalytic activity for H2 production. DFT simulations are used to predict the material properties using quantum mechanical formulations. DFT simulations are therefore employed to study the effects of boron (B) and phosphorus (P) co-doping on the electronic and optical properties of GCN. The co-doping of boron (B) and phosphorus (P) atoms at carbon and interstitial sites within the GCN lattice influences the behaviour of charge carriers

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and electronic transitions within the material. The electronic and optical properties of a material that are crucial for its photocatalytic activity are significantly influenced by B and P dopants via band structure and optical properties of doped GCN. Considering the band structures of different doped GCN systems, it was noted that B-doped GCN exhibited a metallic property. P-doped GCN, in contrast, exhibited a half-filled metallic property quite different from B-doped GCN. When boron and phosphorus are co-doped into GCN, the resulting material exhibits a bandgap of 1.95 eV. This kind of band gap engineering is useful for facilitating light absorption and photocatalytic reactions. The combination of experimental findings and DFT simulations suggests that multi-elemental co-doping, specifically B and P co-doping, can significantly influence the electronic and optical properties of GCN photocatalysts. Introduction of metal atom species with much larger atomic radii compared to C and N is highly unlikely to replace C or N atoms in GCN lattice or settle as interstitials. In most of the metal modified s-triazine-based GCN systems, the metal atoms are adsorbed above the interstitial site and bond to three adjacent N atoms. This situation is better described by a term known as metal decoration. This decoration of metal atom needs adsorption or binding energy. Commonly, DFT simulation of metal-decorated GCN systems included alkali and transition metals such as Sc, Ti, V, Cr, Mn, Fe, Co, and Ni. It is quite likely that the strong reduction capability of Sc-, Ti-, and V-decorated GCN systems offers better water splitting for H2 production. The electrostatic potential profiles calculated indicated that the transition metal-decorated GCN systems possess a smaller work function than that of pristine GCN.

4 Nanocomposites Improved performances of nanocomposite photocatalysts make it important to explore various options available in GCN-based composites as discussed below. Nanocomposite photocatalysts are composed of two or more different components, often at the nanoscale, that work together to enhance their photocatalytic properties. These composites can harness the advantages of individual components, such as their light absorption properties or charge carrier separation efficiency, leading to improved overall photocatalytic activity. A 2D-GCN-NS can serve as a promising semiconducting component in a nanocomposite due to its superior photo-absorption capability to generate more charge carriers upon illumination. DFT simulations are used to predict the electronic properties as a function of chosen lattice structure. In the context of nanocomposite photocatalysts, DFT simulations facilitate analysing the interactions between different components to predict the photocatalytic behaviour of the composite. Several types of GCN composites have been studied, including GCN/metal oxide, GCN/metal chalcogenide, GCN/Bi, and GCN/Zn combinations.

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The interfaces between different components in a nanocomposite decide the overall photocatalytic activity via charge separation, transport, and recombination, all of which are vital for efficient photocatalysis. Calculating the charge density difference in a nanocomposite provides insights into the redistribution of charge carriers upon photoexcitation which helps in understanding the charge transfers occurring between different components and contributing to the overall photocatalytic activity. Larger work functions correspond to lower Fermi levels, and consequently, a difference in work functions between different materials can influence the direction of electron flow and charge transfer at the interfaces influencing the photocatalytic activity. In a junction (homo and hetero), there exists a built-in potential due to the difference in the Fermi levels of the two materials which creates an electric field that opposes the diffusion of charge carriers across the junction, leading to form a depletion region under equilibrium and create built-in potentials that influence the behaviour of charge carriers’ transport. When two different materials come into contact, alignment of their Fermi levels causes the exchange of charge carriers at the interface. This alignment influences the energy levels available for charge carriers transport in the composite material. When photons are incident on a semiconductor material, it can generate electron– hole pairs, by exciting an electron from VB to CB. The movement of these charge carriers contributes to electrical current. The direction of charge carrier transfer depends on the energy levels and potential barriers within the material as discussed. An electron in the context of charge transfer in a composite material can potentially capture photogenerated electrons. The interplay of work functions, Fermi level alignment, and relative CB positions in different materials within a composite influences the direction of photogenerated charge carrier transfers. Understanding these processes helps in designing and optimizing materials for various optoelectronic devices like solar cells and photodetectors. The photogenerated electrons and holes are sorted out in two groups, e.g. with lower and higher redox capabilities across the Z-scheme heterostructure. This kind of charge carrier screening facilitates the reduction and oxidation reactions at the different sides of the interface. Using Pt, Pd, and Au as co-catalysts was examined to promote the charge separation and enhancing the photocatalytic activity of GCN. These co-catalysts aided in the transfer of charge carriers during photocatalytic processes noted as follows: Pt, Pd, and Au co-catalysts in conjunction with GCN could improve the efficiency of photocatalytic reactions. These metals play a crucial role in promoting the separation of photogenerated charge carriers. GCN in contact with Pd allows the electrons to transfer to Pd co-catalyst leading to a change in the energy band structure, creating an upward bend in CB of Schottky barrier. The work function of GCN (4.31 eV) is lower than that of Pd (100) (5.05 eV) and Pd (111) (5.23 eV). Such work function mismatches influence the charge carrier transfer due to energy alignment between the GCN and Pd.

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The Fermi level of Pd remains constant during the charge transfer, while the Fermi level of GCN shifts downwards to align with that of Pd. This alignment enhances the separation of charge carriers. When exposed to light, photogenerated electrons in CB of GCN migrate towards the Pd co-catalyst, and photogenerated holes remain in the VB of GCN. The Schottky barrier formed at the GCN-Pd interface effectively prevents the backflow of electrons from Pd to GCN. This barrier enhances the retention of charge carriers at the co-catalyst interface, contributing to the overall photocatalytic activity. DFT study of various types of porous b-GCN and nanostructures was carried out in case of nanowires, nanoclusters, nanoribbons, and nanotubes with the following observations. Regarding fabrication of various GCN nanostructures, there are only a few reports that have utilized DFT calculations. DFT provides the electronic structure, energetics, and properties of materials at the atomic level. While analysing the hollow GCN nanoclusters, the combinations considered employed C/N stoichiometry from 0.69 to 0.82. The formation energy of nanoclusters was noted to be positive which decreased with increasing number of the different constituent atomic species and finally approached the formation energy of a pristine GCN monolayer (0.209 eV/ atom). MD simulation was carried out at 700 K to assess the structural stability of the nanocluster. Three nanoclusters, namely C18 N26 , C30 N40 -C3 , and C36 N48 , were found unchanged during the simulation. The GCN nanoribbons were modelled by tailoring a planar GCN monolayer ribbon with H termination of the two edges. In pristine GCN nanoribbon, the bridge N atoms, which connected neighbouring triazine units on the N-exposed edge, were saturated with hydrogen atoms. The hydrogenated GCN nanoribbon was thus considered as an electron-doped GCN system. The band structure of pristine GCN nanoribbon exhibits a direct band gap semiconductor. The spin-up and spin-down band structures of the hydrogenated GCN nanoribbon exhibit a metallic property and a semiconducting nature with an indirect bandgap, respectively. With enlarged nanoribbons, both the bandgap of pristine GCN nanoribbon and the spin-down bandgap of hydrogenated GCN nanoribbon gradually decrease and finally converge to equilibrium value. The MD simulation showed that pristine GCN and hydrogenated GCN nanoribbons prevail in low and high H2 concentration, respectively. Various aspects of single-walled GCN-NTs were analysed, such as their stability, strain energy, and band structures. The key findings from are listed below: Single-walled GCN-NTs were imagined as rolled up form of a planar GCN monolayer. Different rolling directions led to the formation of armchair and zigzag NTs. The calculated strain energy of the constructed NT models was compared to that of the planar GCN monolayer in which all the created NTs were found more stable than the planar monolayer, except the (4, 4) NTs. Among the armchair and zigzag NTs, zigzag NTs were more stable than armchair ones, except the (8, 0) zigzag NTs. The (14, 14) armchair and the (14, 0) zigzag NTs were the most stable NTs among their respective configurations. They had

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strain energies of −0.199 eV and −0.333 eV, respectively. Band structures of the nanotubes had larger band gaps compared to the planar GCN monolayer except for the (4, 4) NTs.

5 Discussion and Conclusions While DFT is a powerful tool to predict the electronic structures and material properties, there are certain complexities in photocatalytic interactions that may not be fully captured by the current theoretical models. Some of these limitations are pointed below: DFT focuses on electronic properties of a given atomic arrangements, but they might not adequately consider the intricate internal mechanisms involving photon absorption, charge generation and transfer, surface reactions, and more in a photocatalytic process. Photocatalytic reactions often involve adsorption of reactants and intermediates onto the catalyst’s surface, followed by modifications in surface redox reactions. DFT might have limitations in accurately predicting the adsorption energies and reaction pathways of these species on the catalyst surface. While DFT can take care of ground-state electronic structures, it might not fully account for excited states that are crucial for understanding photocatalytic processes. The study of electronic excitations and band transitions typically requires more advanced methods beyond DFT, such as time-dependent DFT or GW calculations. Photocatalytic reactions often take place in a solvent or in the presence of other environmental factors. DFT might not fully account for solvation effects, which can determine the reaction pathways and kinetics. Photocatalytic reactions involve quantum dynamics, which might not be accurately described by static DFT. Quantum mechanical simulations explicitly incorporating the time evolution, such as MD or transition state theory, could provide a more comprehensive understanding of reaction mechanisms and rates. DFT might not fully capture the influence of defects and the detailed surface morphology of the catalyst. These factors can strongly influence photocatalytic activity and selectivity. Some of these above-mentioned effects and mechanisms require more advanced computational methods that can be computationally expensive and challenging to implement. Despite offering valuable insights into the electronic properties for a given structural arrangements of materials like s-triazine-based GCN, the DFT simulations do need to consider these limitations more novel techniques to gain a better understanding of the photocatalytic interactions. Advanced computational methods, experimental studies, and advanced characterization techniques can jointly help to bridge the gaps between theoretical predictions and experimental observations in the field of photocatalysis.

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A breakdown of the issues is highlighted below: The process of light irradiation and photoexcitation is a dynamic process involving the absorption of photons and excitation of electrons to higher energy states. This transition and the generation of charge carriers (electrons and holes) are not explicitly captured by the static DFT calculations. Time-dependent DFT or other advanced methods would be necessary to study these dynamic processes. The choice of specific facets with exposed surface atoms in a material greatly influences its properties and interactions. However, there is no universal standard for selecting these facets, and the intricacies of interfacial interactions make it challenging to accurately model. Describing the interfaces and contacts between different materials in experimentally synthesized composite photocatalysts is indeed a complex structure. These interfaces can significantly affect reaction pathways and charge transfer, but their accurate representation in simulations is difficult due to the variety of possible interactions and structural arrangements. Most DFT studies employ simplified models, like ideal monolayer GCN, for computation. However, these models might not represent the full experimental conditions. Factors like incomplete polymerization during calcination and the presence of thicker GCN layers are important to significantly influence the photocatalytic behaviour. Addressing these challenges requires a combination of theoretical, computational, and experimental efforts: Transitioning from static DFT to time-dependent DFT or other advanced computational techniques can provide better insights into the dynamic processes, electronic excitations, and charge carrier generation. While modelling interfaces accurately is challenging, methods such as DFT with van der Waals corrections (DFT + vdW) and quantum mechanics/molecular mechanics (QM/MM) approaches might offer insights into interfacial interactions. Developing more realistic models that consider factors like incomplete polymerization, thickness variation, and the presence of defects is crucial for bridging the gap between theoretical predictions and experimental observations. Collaborations between experimentalists and theorists can help validate theoretical models against real-world experimental data and provide insights into the most relevant factors to consider. Machine learning techniques can be employed to extrapolate from available data and predict properties of materials and their interactions beyond the scope of traditional simulations. In essence, while DFT simulations are valuable tools, they have limitations in capturing the complexities of photocatalytic interactions. Combining various computational methods, experimental insights, and innovative approaches is essential for a comprehensive understanding of photocatalytic processes and the development of efficient photocatalytic materials. Incorporating redox reactions, exploring charge carrier transfer channels, and enhancing electronic delocalization are crucial for advancing the understanding and design of efficient GCN-based photocatalysts. Some of the points needing better understanding are given below:

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Redox reactions involving electron transfer play a central role in photocatalysis. Photogenerated charge carriers (electrons and holes) are involved in these reactions, leading to the activation of reactants and the eventual formation of products. Future DFT simulations should strive to explicitly consider these redox reactions, including the interactions of charge carriers with adsorbates and catalyst surfaces. Understanding the pathways through which charge carriers move within a photocatalyst is crucial for optimizing photocatalytic efficiency. Future investigations are needed in identifying and characterizing these charge carrier transfer channels, including their energetics and kinetics. Advanced computational techniques, such as non-adiabatic MD, can help simulate charge transfer processes in real time. Manipulating the HOMO and LUMO levels can enhance the photocatalytic activity of a material. Introducing non-metal atomic species at specific positions or grafting organic molecules onto the photocatalyst surface can alter the electronic structure, leading to increased charge delocalization and improved charge separation. Investigating unique structural configurations and exploring various charge transfer pathways can provide insights into the factors influencing photocatalytic activity. Theoretical models should be validated against experimental data to ensure their accuracy and reliability. Collaborations between experimentalists and theorists can help refine models and guide future simulations to better match real-world behaviour. To enhance the accuracy and applicability of theoretical models, it is crucial to consider a variety of scenarios and interactions. Here are some considerations for future studies in this area: Exploring different types of GCN-NS modifications, such as corrugated, defective, elementally doped, or metal-decorated structures, is vital. Each modification can introduce unique electronic, structural, and chemical properties that impact adsorption behaviour. Simulations should encompass these modifications to provide a comprehensive understanding. Accurate determination of adsorption energies and interaction strengths between adsorbates and GCN-NS surfaces is crucial to account for van der Waals interactions, such as DFT + vdW or hybrid functionals, which might be necessary to correctly describe weak interactions in adsorption processes. Comparing adsorption behaviour on both pristine and modified GCN-NS can reveal how surface modifications influence adsorption sites and strengths. This can lead to insights into how modifications affect catalytic activity. Investigating the influence of co-adsorbed molecules and competitive adsorption is essential for understanding complex reaction environments. How different molecules compete for adsorption sites can significantly impact reaction selectivity and kinetics. Identifying preferential adsorption sites on the GCN-NS surface for different reactant molecules provides insights into the most active sites for catalysis. This can guide experimental efforts to design materials with improved photocatalytic properties.

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Varying the density of adsorbed molecules can impact surface coverage and reaction pathways. Exploring the effects of different coverage levels can help elucidate surface-reactant interactions. Considering thicker layers of adsorbed molecules can provide a more realistic representation of experimental conditions. This could be particularly relevant when dealing with larger molecules or complex adsorption geometries. Advanced techniques such as ab initio molecular dynamics (AIMD) can capture the dynamics of adsorption and desorption processes, providing insights into adsorption kinetics. Despite the limitations of experimental measurements due to the rapid nature of these reactions, theoretical approaches, such as TD-DFT simulation, can offer valuable insights into the underlying mechanisms. How these aspects can be further explored is given below: Determining the step-by-step reaction pathways is crucial for understanding the entire photocatalytic process. TD-DFT can provide insights into the excited-state dynamics of photogenerated electrons and holes, including their interactions with adsorbates and surface sites. TD-DFT can help identify the pathways that photogenerated charge carriers follow, the associated energy barriers they need to overcome, and the rate-determining steps in the reaction. This information is essential for predicting reaction kinetics and understanding how specific modifications influence the energy landscape. Investigating various forms of GCN-NS, including pristine, doped, and metaldecorated structures, allows for a detailed comparison of their photocatalytic mechanisms. This can reveal how different modifications impact charge carrier transitions, energy barriers, and overall reaction pathways. While energy band structures, density of states, and energy gaps provide essential electronic structure information, they do not capture the full complexity of photocatalytic interactions. Incorporating TD-DFT and other advanced methods can provide insights into excited-state properties, charge transfer dynamics, and reaction pathways. Theoretical predictions should be compared with available experimental data to validate the proposed reaction pathways and mechanisms. This iterative process ensures that theoretical models accurately capture real-world behaviour. Combining TD-DFT calculations with other computational techniques, such as MD or kinetic Monte Carlo simulations, can provide a multiscale view of photocatalytic processes. This approach allows for the exploration of longer timescales and larger system sizes, which are often necessary to capture realistic reaction kinetics. By taking these considerations into account and integrating TD-DFT calculations with other computational and experimental techniques, it can help to gain a deeper understanding of the intricate mechanisms underlying photocatalytic reactions on GCN-NS. This holistic approach can lead to more accurate predictions of photocatalytic activity and guide the design of efficient photocatalysts for various applications.

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Acknowledgements The authors express their gratitude to Dr. (Ms.) Malti Goel, CEO, Climate Change Institute, Delhi, for her encouragement to undertake this study of hydrogen generation by splitting water using g-C3 N4 -based nanomaterials and the large variety of the related composites.

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Hydrogen Production from Biomass Rajan Varshney

Abstract Hydrogen is light, storable, energy heavy and does not produce direct carbon emissions or greenhouse gases (GHG). So, hydrogen can play an important role in any decarbonization strategy. It will not only help in integrating increasing RE into the grid sustainably but can also decarbonize hard to abate sectors like petroleum, steel, cement, fertilizers, transport, etc. Presently, green hydrogen from electrolysis of water costs twice that of grey hydrogen but with alternate technologies, soon it may be available at less than $1/kg. Green hydrogen can be produced from renewable feedstocks like waste, biomass, sewage sludge, etc. Processes for hydrogen production from waste include gasification, pyrolysis, anaerobic digestion, steam methane reforming, dry reforming, methane splitting, etc. Global waste generation is over 2.0 billion tons and expected to grow about 3.5 billion tons by 2050. Out of various hydrogen production routes, analysis indicates hydrogen from biomass/ waste not only can be produced at least cost but also can reduce air, water and soil contamination. Moreover, hydrogen from waste produced in decentralized manner can reduce hydrogen transport cost. Further, green hydrogen can facilitate faster and sustainable energy transition cutting energy imports for India. Green hydrogen can make India self-reliant and facilitate its journey towards carbon neutrality. Learning objectives • Cost-effective production of hydrogen from biomass • Benefits of using biomass waste conversion into hydrogen production • Recommendations for utilizing waste biomass for producing green hydrogen Keywords Hydrogen production · Biomass · Financial analysis · Policy recommendations

R. Varshney (B) C1/ 72, Mangal Apartment, Vasundhra Enclave, Delhi 110096, India e-mail: [email protected]

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Goel and G. Sen (eds.), Climate Action and Hydrogen Economy, Green Energy and Technology, https://doi.org/10.1007/978-981-99-6237-2_10

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Abbreviations AEM CCS FCEV GHG HTSE MSW NHEM PEM SMR SOE

Anion Exchange Membrane Carbon Capture and Storage Fuel Cell Electric Vehicles Greenhouse Gases High-Temperature Steam Electrolysis Municipal Solid Waste National Hydrogen Energy Mission Proton Exchange Membrane Steam Methane Reforming Solid Oxide Electrolyser

1 Introduction As a step in the direction of hydrogen energy during the 75th anniversary of India’s independence, Prime Minister Narendra Modi announced National Hydrogen Energy Mission (NHEM), on 15 August 2021 with the goal of promoting hydrogen economy for reducing carbon emissions and increasing the use of renewable energy sources. The first phase of hydrogen policy released on 17th February 2022 includes measures to increase green hydrogen production with lower cost and thus promoting its applications. The main goal of COP 26 is to limit the global temperature rise to 1.5 °C from pre-industrial level to avoid the most dangerous climate change. Climate change and extreme weather patterns are making human survival difficult. India’s commitment of 500 GW RE in COP26 can be very well met leveraging immense waste available quite easily. Mostly, the waste is being dumped in landfills or incinerated. This creates huge problems contaminating air, water and soil. Handled judiciously, waste can be a rich source for energy, building energy security, improving soil fertility and improving the environment on the whole. Global waste generation is over 2.0 billion tons and expected to grow about 3.5 billion tons by 2050. Hydrogen is part of any decarbonization strategy. It can meet the requirements of energy transfer, storage, etc., and can also be used as feedstock for many industrial uses and can help decarbonize hard to abate sectors. Thus, hydrogen from waste is at the core of the triad of energy, economy and environment. The country has ample sunshine and vast shoreline. Leveraging the country’s competitive solar and wind tariffs, it can lead to production of low-cost green hydrogen and ammonia. Clubbing green hydrogen generation from waste can help in making India a large exporter of green hydrogen. India is currently the third-largest producer of greenhouse gases. Growing air pollution poses serious health hazard and may affect productivity and GDP. The evergrowing demand for vehicles and the demand for motorable roads have led to cutting

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of trees, besides pollution from automobile exhaust. Characteristics of hydrogen fuel such as long-range, high-energy density, quick refuelling and lower extraction of precious rare earths make it better choice than a battery vehicle. However, high cost of electrolysers, fuel cells and lack of infrastructure are some of the challenges to be overcome with more penetration, technological advances and resultant economies of scale with bold policies, regulations and incentives. Many developed countries like USA, European Union, Japan and South Korea are now concentrating on hydrogen economy. Indian companies like Reliance, Adani, L&T and many public sector companies have announced big plans and investments for hydrogen. Its relevance is not clear. Government funding, favourable policies, production linked incentive schemes for electrolysers, fuel cells, etc., including the value chain are in the works and shall help reduce the cost of green hydrogen and also cost of fuel cells vehicles (FCEV).

2 Hydrogen Production 2.1 Colours of Hydrogen Hydrogen can be classified into four categories based on the source of production and carbon emission: 1. Grey Hydrogen: Hydrogen from hydrocarbons (natural gas and fossil fuels) is called grey hydrogen. This is the most well-known technique for production of hydrogen presently. In this process, carbon dioxide is produced as a by-product. 2. Black/Brown Hydrogen: This is the most traditional method for producing hydrogen and includes changing coal into gas. The hydrogen delivered is called brown if lignite coal is utilized and black if bituminous coal is utilized for the cycle. It is a profoundly pollution causing process as both carbon dioxide and carbon monoxide are released into the atmosphere which cannot be reused. 3. Blue Hydrogen: This is the hydrogen delivered from hydrocarbons where the emissions produced from the process are caught and stored underground by industrial carbon capture and storage (CCS). Subsequently, it is viewed as a preferable option over grey hydrogen where the emissions are delivered. Although, even in this interaction, around 10–20% of the carbon dioxide is unable to be captured. 4. Pink Hydrogen: This is the hydrogen generated by nuclear energy. The selection of hydrogen technologies greatly depends on the type of the nuclear power plant. Some hydrogen production technologies, such as conventional electrolysis, require only electric power, whereas others, such as thermochemical cycles, may require only process heat (which may be delivered at elevated temperature values) or hybrid technologies such as the high-temperature steam electrolysis (HTSE).

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5. Green Hydrogen: Green hydrogen is produced using renewable sources of energy like sunlight and wind for water splitting into hydrogen and oxygen through electrolysis. This is the cleanest type of hydrogen production since the results are simply water and water vapour. Also, hydrogen generated from waste also is green hydrogen as it is produced from renewable biomass and whatever CO2 is released is absorbed by plants and is not from fossil fuels.

2.2 Hydrogen Generation Pathways a. Steam Methane Reforming (SMR) SMR process has been used to produce hydrogen commercially from natural gas (NG) since 1930 and even today more than 70% H2 is produced via SMR. It is a two-step process: (1) The first step is called SMR reaction and can be represented by following chemical equation: CH4 + H2 O → CO + H2 (2) The second step is called water–gas shift reaction (WGSR), and its equation is given below: CO + H2 O → CO2 + H2 NG contains methane, and it reacts with steam at high temperature (750–9500 °C) and at a pressure of around 15–20 atm to produce H2 in addition to CO and CO2 in the presence of nickel. Then CO reacts with steam to produce more H2 and CO2 . WGSR requires the presence of a catalyst like iron oxide doped with chromium oxide. The main disadvantage of SMR process is that one ton of H2 results in production of 9–12 ton of CO2 . b. Partial Oxidation of Methane In partial oxidation, methane is partly oxidized in the presence of stoichiometrically insufficient O2 for complete reaction or very little O2 and results in production of H2 and CO. Then CO reacts with steam to produce more H2 and CO2 via WGSR. CH4 + 0.5O2 → CO + 2H2 CO + H2 O → CO2 + H2

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c. Coal Gasification Coal is gasified in a gasifier with steam and oxygen to produce a mixture of H2 , CO, steam and O2 syngas at very high temperature and medium pressure. Further syngas is reacted with more steam in a water–gas shift reactor to produce more H2 and CO2 via WGSR. d. Electrolysis Electrolysis is a well-developed process for splitting water to H2 and O2 and is available commercially the breaking down of water molecules into hydrogen and oxygen using electricity. This technology is well developed and available commercially. An electrolyser contains electrodes called anode and cathode which are separated by an electrolyte. Four types of electrolysers, viz. alkaline electrolysers (AE), proton exchange membrane (PEM), solid oxide electrolyser (SOE), and anion exchange membrane (AEM), are available. In addition, some other types like plasma electrolysers, etc., are under various stages of development (Table 1). e. Direct Solar Water Splitting Processes Here energy of sunlight or light is used to split water into H2 and O2 . These processes are in research and early stages of development. Though, these methods may take some years to reach market but can offer cost-effective method of H2 production with minimal environmental impact. These require photocatalysts. The photo-splitting of water can be classified intro two types: (a) photo-biological and (b) photo-electro-chemical splitting: • Photo-biological Methods—Here micro-organisms like algae are used to split water into H2 and O2 in the presence of light similar to photosynthesis wherein plants produce O2 . These micro-organisms feed on water and evolve hydrogen Table 1 Comparison of types of electrolyser Description

Unit

Alkaline

PEM

SOE

AEM

Moderate

High

High

High

20–25

10–20

10–15

10–12

Technology readiness level

9

9

8

7

Operating temperature

Low

Low

High

Low

9

9

9

9

63–70%

56–60%

74–85%

55–69%

Cost Lifetime

Water requirement

Years

Litre/litre of H2

Efficiency Start-up time

Minutes

>25, medium

80% of energy

Sustainable Pathways for Hydrogen Production via Molecular Catalysts

(a)

3% 2% 26%

Petrolium 44%

18% Coal Natural gas

25%

(b)

Hydroelectr ic power Nuclear power

197

3.9% 0.1%

Natural gas 48%

30%

Oil Coal Electrolysis Others

Fig. 1 a Major resources of the global energy supply and b Currently deployed hydrogen production sources

production all around the world (Fig. 1a), which is associated with the unavoidable production of CO2 . Therefore, by looking at the present scenario, major countries around the world, including India, have taken the pledge at the recent climate change summit to reduce CO2 emission. Most countries are leading activities for achieving a net zero carbon scenario in the next few decades [4]. Some of the possible methods to mitigate carbon dioxide in the atmosphere comprise reduction in energy demand, electrification of energy, decarbonization of electricity, carbon dioxide storage, and sequestration in geological reservoirs [5]. The development of alternative energy resources is also essential in this pursuit, as they minimize CO2 production during energy harvest. However, the intermittent nature of renewables, along with their low energy density, has severely impeded their worldwide usage. Facile conversion of these energy resources into a stable and reliable chemical mediator can provide a viable solution to this existing issue. During photosynthesis, biology follows the same strategy, where solar energy is captured in chemical bonds (glucose), which can release the energy appropriately as per the requirement later. This strategy can be simplified by capturing renewables in the form of H–H bond energy via proton to H2 conversion [6]. Therefore, the use of hydrogen (energy density ~ 142 MJ/kg) as a sustainable fuel is anxiously awaited by the world [7]. Additionally, using hydrogen as a fuel could aid in reducing environmental pollution since it emits no harmful substances. Although it is the third most common element on earth, the presence of hydrogen gas is rather infrequent in the earth’s atmosphere (1 ppm by volume) [8, 9]. On the other hand, the unique chemical and physical properties of hydrogen gas, its production, storage, and transportation present a wide range of difficulties as well as safety risks [10]. Catalytic systems that can continuously produce green hydrogen from hydrogen sources are therefore crucial for the advancement of a greener future. Green hydrogen offers a unique proposition as it can be considered as a vertical for CO2 capture, utilization, and sequestration (CCUS) technology. In addition, hydrogen can be generated from biomass that reflects a carbon–neutral energy harvest. Hydrogen is a known chemical in the commercial market, which is deployed in large amounts (on a scale close to million tons) in industrial sectors [11–13]. Currently, the majority of this H2 is produced from steam methane reformation (~48%), while coal gasification accounts for ~18% of H2 production (Fig. 1b).

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Auto-thermal reforming, partial oxidation, and steam reforming are the conventional ways of generating hydrogen from natural gas. The other resources of commercial hydrogen are oil/naphtha reforming in refineries and chemical industry off-gases (30%), water electrolysis (3.9%), and other sources (0.1%) [11, 14]. Among these processes, the fossil fuel-derived H2 production methods (steam methane reformation, coal gasification, and oil/naptha reformation) also produce CO2 . Hence, these H2 production technologies are assigned as gray or brown H2 [15]. If hydrogen is produced from water with the use of renewables, then it is designated as green hydrogen technology as it doesn’t contain any direct carbon footprint. In this chapter, such green chemistry of hydrogen production is depicted in detail by categorizing it into three portions: i. electrochemical, ii. photochemical, and iii. biological methods [16]. We have also included a section on thermal hydrogen production as it still remains the major H2 generation technique.

2 Thermal Production of Hydrogen Hydrogen production via thermal process is a widely utilized pathway for commercial production. In this method, by-products such as CO2 and CO are generated along with hydrogen, where fossil fuels are processed under high temperature and pressure scenarios [17]. Hence, the separation of the by-products is essential for obtaining pure hydrogen. The inclusion of such separation technology invariably increases the overall operational cost [18]. However, the availability of the hydrocarbon feedstock and established industrial-scale technology ensure that this process provides the minimal production cost for hydrogen among all the existing methods. Therefore, steam methane reformation (SMR) remains the most popular hydrogen production method despite greenhouse gas (GHG) emissions [16]. Currently, SMR accounts for almost half of global hydrogen production [16, 19]. In the following, the major reactions occurring during the SMR are depicted (Eqs. 1–3). CH4 + H2 O → CO + 3H2 H0298K = 206 kJ/mol

(1)

CO + H2 O → CO2 + H2 H0298K = −41 kJ/mol

(2)

CH4 + 2H2 O → CO2 + 4H2 H0298K = 165 kJ/mol

(3)

In the first step, the methane reformation in the presence of steam produces hydrogen along with CO [16, 20]. Next, the evolved CO is transformed into additional H2 and CO2 through the water gas shift reaction (WGS). Thus, CO2 becomes an unavoidable by product created during the methane reforming process [19]. In order to make this process environmentally benign, the produced CO2 needs to be captured via appropriate CCUS technology. Therefore, the thermally produced hydrogen gas can be purified and considered as blue hydrogen following the removal of CO2 .

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Except for the SMR process, the other sources of thermal hydrogen production are coal gasification, oil/naphtha reforming in refineries, and the processing of chemical sector off-gases, where a significant portion of commercial hydrogen is originated. The coal gasification operates at a very high temperature (ranging from 700 to 1700 °C) as hydrogen is produced alongside carbon-based by-products [21]. When steam and coal react at pressures below 10 MPa and temperatures over 750 °C, “synthesis gas” (also known as syngas) is typically generated. This syngas is primarily made up of CO and H2 , with varying amounts of CO2 and CH4 [20]. As the production of syngas is an endothermic reaction, it requires the supply of enormous amount of heat to drive the reaction forward. This additional energy demand is conventionally accommodated via the burning of additional coal inside the reactor or supplying heat from outside. Either of these processes makes syngas production energy intensive and has a significant carbon footprint. Therefore, coal gasification is reckoned as an environmentally adverse brown hydrogen production technology, despite its significant share in global hydrogen production [20]. Furthermore, the 30% contribution comes from oil/naphtha reforming in refineries/chemical sector off-gases, which is again an intensive energy-intensive process and produces various toxic by-products [22].

3 Electrochemical Hydrogen Production Water electrolysis is reckoned as one of the leading processes for generating hydrogen with a minimal carbon footprint [23]. Here, the direct application of electricity triggers the splitting of water. The generation of this electricity from renewable energy resources ensures true carbon–neutral energy conversion tactics [23, 24]. The produced hydrogen via electrolysis stores renewable energy, which can be transformed into electricity again with the use of fuel cells, as this process produces water in combination with aerial oxygen [25]. However, the process of generating hydrogen from water requires a lot of energy. The ultimate goal of using H2 as a clean alternative fuel is to optimize the reduction and oxidation reactions occurring in the cathode and anode, respectively (Eqs. 4–5) [26]. This process is constrained by the requirement for a high voltage to catalyze the oxygen evolution reaction (OER), which is the counter step in the oxidation of water and for which the theoretical decomposition voltage is 1.23 V [27]. The generation of oxygen at the anode results in the generation of H+ and e-, which combine at the cathode to form hydrogen [27, 28]. Additionally, the HER, which is a two-electron transfer process at the cathode, depends on multiple factors regulating the surrounding conditions. Therefore, by creating a catalyst that is efficient for both the hydrogen evolution reaction and the oxygen evolution reaction, it is possible to create the two compartments setup separated by a membrane that produces pure hydrogen at the cathode (Fig. 2) [29]. At anode 2H2 O (l) → O2 (g) + 4H+ + 4e−

(4)

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O2

anode +

H2

cathode -

-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

+

-

Fig. 2 Schematic diagram of the water electrolyzer leading to green hydrogen production

At cathode 4H+ + 4e− → 2H2 (g)

(5)

Numerous reports are available in the literature where an array of materials has been deployed for proton reduction. These investigations demonstrate that there are two primary pathways exist for hydrogen production: i. homolytic and ii. heterolytic, as shown in Fig. 3 [30]. i. The homolytic pathway: This hydrogen production route follows a reductive elimination mechanism, where two-metal hydride intermediates combine to produce one molecule of hydrogen. Here, the electron transfer to each metal site occurs either before protonation or after hydride production. ii. Heterolytic pathway: In this pathway, two electrons are added to one metal center, which can proceed either alternately or sequentially with a proton exchange to produce a metal hydride intermediate. A second proton attacks the metal hydride species in the next step to generate a hydrogen molecule. Both these mechanisms can drive the electrocatalytic H2 production that is subtly regulated by the reaction conditions [30–33]. H

Fig. 3 General mechanism pathway for homogeneous proton reduction

H2

[Mn+1]

e-

[Mn+]

H [Mn] H+

H

e-

[Mn+1] H2

[Mn-1]

H+

H+, e-

[Mn+]

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The electrolytic pathways can be distinguished based on the phase of the catalyst during the reaction. If the catalyst molecule remains in the solution phase while functioning on the electrode-solution interface, it is designated as homogenous catalysis. On the other hand, if the catalyst is anchored on the electrode surface and drives the reaction via a solid phase, it is defined as heterogeneous catalysis. A number of procedures involving both homogeneous and heterogeneous catalysts have been explored for hydrogen production from water to date. The development of a watersoluble catalyst for hydrogen production is always attractive due to its operational advantages [34–38]. In this regard, several cobalt complexes synthesized in a salen-based ligand framework were investigated, where they demonstrated substantial hydrogen production under acidic conditions. Interestingly, these complexes displayed a unique influence from the ligand scaffold on their reactivity, which was attributed to outer coordination sphere (OCS) effects [39]. Such an effect is a hallmark of metalloenzymes, which were strategically replicated in an organic template with the strategic incorporation of natural amino acids on the periphery of a salen-type ligand. The combination of salen and tyrosine showcased the best performance among this group of homogeneous catalysts, consisting of phenylalanine, benzylamine, and the control nonfunctionalized salen. Interestingly, their hydrogen production was mostly limited in the pH 2–4 region. A detailed spectroscopic analysis revealed the participation of peripheral carboxylic acid groups in the reactivity. At pH > 4, the carboxylic acid was deprotonated to generate carboxylate, which coordinates with the metal center. Here, not only the protonation site is blocked, but it also restricts the proton relay via the carboxylic acid group. However, below pH 4, the carboxylic acid group dominates in its protonated form, where it is released from the metal coordination, and it resumes proton transport around the metal center to trigger the electrocatalytic hydrogen production. Such a pH switch has been rarely observed for synthetic electrocatalysts. The salen-tyrosine bound complex C1 exhibited an electrocatalytic hydrogen production rate (TOF/turnover frequency) of 190 s−1 along with the over potential of 775 mV (Scheme 1). Cobaloxime complexes represent another genre of cobalt-based catalysts that display promising H2 production activity from water. The template of this complex is prepared by coordinating two molecules of dimethylglyoxime ligands with one equivalent of cobalt (III) center. This basic template is inactive for hydrogen production. However, with the inclusion of an axial pyridine ligand, the cobalt core becomes an active hydrogen evolution catalyst, albeit at a poor rate and limited activity only under an acidic organic medium [40]. Again, our group deployed the strategy of appending OCS functionality to boost their reactivity following the hints from biology. Metalloenzymes, such as hydrogenase, have specifically positioned [Fe4 S4 ]. clusters as electron transporting units along with tactically oriented protic functionalities (derived from amino acid side chains), which creates a dynamic outer coordination sphere [41]. As homogeneous electrocatalysts can exchange electrons rapidly from the electrode-solution interface, we primarily looked into designing the protonexchanging network around the catalyst. Here, we have functionalized the axially coordinating N-heterocycles to introduce remotely influencing protic functionalities

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Co

O C1

-

O C

N

H 2N

C3

Cl

H O N Co N N O H O N

HO CH2 C N HOOC H H

COOH

N

C2

O N

Cl

H O N Co N N O H O N O N

OH

Cl

H O N Co N N O H O N O N

Cl

H O N Co N N O H O N O N

Cl

H O N Co N N O H O O N

N HO

O P HO OH O

O

HO

C4 C5

C6

Scheme 1 Variable molecular catalysts explored for hydrogen evolution reaction (HER) in an aqueous solution

around the cobalt core. These functionalities ensure water solubility, allowing us to explore electrocatalytic hydrogen production in aqueous solutions. Cobaloximebased catalyst is more effective due to the unique structure of the cobaloxime core, and further adding the axial electron-donating/-withdrawing substituents in the primary coordination sphere influences their electrocatalytic hydrogen activity [41]. The cobaloxime core, upon addition of an axial pyridine (C2), exhibits reversible Co(II)/Co(I) and irreversible Co(III/II) redox signatures in dry organic environments [42]. The irreversibility of the Co (III/II) transition is linked to the loss of an axial ligand (Cl− in most cases) from the cobalt center. The catalytic response typically sets in around the Co (II/I) signal as the reductive current continues to increase with the increase of acid in the solution. The replacement of the methyl groups on the dimethylglyoxime moiety with phenyl groups adversely impacted electrocatalytic hydrogen production as it not only reduced the catalytic rate but also increased the overpotential requirement (the difference between the applied potential and standard reduction potential for H2 evolution at the experimental conditions) [43]. The inclusion of imidazole in place of pyridine improved the overpotential requirements. The presence of additional protic functionalities (C3) further enhanced the hydrogen production rate [44]. The decoration of the pyridine motifs also resulted in the generation of a new class of catalysts that expanded the activity of the parent pyridine-ligated

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cobaloxime multiple folds. In comparison, the primary amine group (pyridin-4ylmethanamine) outperformed the secondary amine group as well as the analogous cobaloxime template [45]. For the same complexes coordinated with aminebased ligands having 4-ethylpyridine, pyridin-4-ylmethanamine, and N-methyl-1(pyridin-4-yl) methanamine ligands on the axial position of the cobaloxime core. The cobaloxime complex with pyridin-4-ylmethanamine ligation (C4) exhibits the highest TOF among these three complexes (~2500 s−1 ) while operating at a moderate overpotential of 455 mV [45]. Further, it was discovered that several peripheral amino acid-appended catalysts showcase unique features such as water solubility, oxygen tolerance, and acid stability, which boosted their respective HER catalytic activity [46]. Here, the number of specific proton-exchanging groups is critical for the absolute catalytic rate. The cobaloxime core ligated with (pyridin-4-ylmethyl) tyrosine (C5) achieved one of the fastest electrocatalytic hydrogen production rates observed for cobalt-containing homogeneous catalysts. This complex operates at a rate of ~8830 s−1 at pH 7.0 with an overpotential of 507 mV (Table 1) [46]. Later, the potential candidate pool for OCS-replicating groups has been expanded from natural amino acids to vitamin molecules. The different isomeric structures of vitamin B6 (known as vitamers) contain a pyridine framework along with variable protic functionalities, including amine, aldehyde, alcoholic-OH, phenolic-OH, and phosphate. The direct inclusion of the B6 vitamers in the cobaloxime core resulted in the origin of a new genre of synthetic HER catalysts [47]. These vitamer-appended cobaloximes were found to be active for hydrogen production in an aqueous condition. The electrochemical studies demonstrated a quasi-reversible Co(III)/Co(II) redox feature followed by a catalytic response starting from −0.6 V (vs. SHE) and maximizing near −0.8 V (vs. SHE) at pH 7.0. The formation of hydrogen was quantitatively analyzed via a gas chromatography-thermal conductivity detector (GC-TCD). The complementary two-dimensional NMR experiment highlighted the direct participation of the peripheral protic functionalities in rapid proton exchange during catalysis. In the neutral condition, the 3-hydroxy-2-methyl pyridine-ligated cobaloxime complex (C6) outperformed the other vitamer-linked cobaloximes with a rate of ~1370 s−1 (Table 1). Interestingly, the overvoltage of these vitamers coordinated complexes ranges between 330 and 380 mV, which is the lowest observed for cobaloxime-based catalysts for hydrogen production. The catalytic rate of these complexes was enhanced significantly (TOF ~ 3650 s−1 ) under elevated temperatures (~60 °C) while it is also active under photocatalytic conditions (turnover number/ TON ~ 136 in 6 h).

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Table 1 Comparative data for selected molecular cobalt complexes for H2 production from aqueous medium under different conditions Sr. Molecular cobalt catalyst no

Electrocatalytic HER

Photocatalytic References HER

TOF (s−1 )

TON

TON –

OP (mV)

1

Co(Iminopyridine)

6 × 10−4 450

–

2

Co(DmgBF2 )2 (CH3 CN)2

–

442

5 × 105 – (7h)

Berben and Peters [48]

3

CoGGH

–

600

310 (2.5h)

Kandemir et al. [49]

4

Ht-CoM61A

–

830

1.1 × 105 (6h)

5

Co(dmg)2 Cl(4-pyridine tyrosine) 8830

6

CoMC6*a

680

7

Co-salen tyrosine

190

8

Co(dmg)2 Cl(4-ethylamine pyridine)

3800

9

2200

Razavet et al. [40]

Kandemir et al. [50]

507

Dolui et al. [44] 2.3 × 10,400 105 (3h)

Firpo et al. [51]

775

–

Khandelwal et al. [39]

457

–

Dolui et al. [45]

(1- Iaa)Co(Dmg)2Cl

3280

454

–

10 (4-Iaa)Co(Dmg)2Cl

4925

428

–

9200

11 (His)Co(Dmg)2Cl

4525

477

–

12 CoMP11-Ac

–

852

2.5 × 905 104 (4h)

Kleingardner et al. [52]

13 Co(dmg)2 Cl(pyridine)

930

515

–

–

Dolui et al. [46] Mir et al. [47]

12,180

14 Co(dmg)2 Cl(pyridoxamine)

1202

385

98

132

15 Co(dmg)2 Cl(pyridoxal5’-phosphate)

1370

373

136

121

338

72

89

16 Co(dmg)2 Cl(3-hydroxy-2-methyl 863 pyridine)

Dolui et al. [44]

4 Photochemical Hydrogen Production Production of hydrogen with the direct use of photoirradiation is recognized as one of the prime pathways for the facile conversion of solar to chemical energy. In this molecular catalyst-driven photocatalytic HER strategy, three components are essential, and they are a photosensitizer, a sacrificial electron donor, and a catalyst active in an aqueous medium [53, 54]. The process of photochemical HER conventionally initiates with the photoexcitation of the photosensitizer (PS) upon irradiation of light. The photosensitizer attains an excited state PS* at the end of this step. Then, this

Sustainable Pathways for Hydrogen Production via Molecular Catalysts Fig. 4 General mechanism of electron transfer between photosensitizer (PS), catalyst (Catn ), and electron donor (ED), leading to the formation of the reduced catalyst during the photocatalytic cycle

hν Reductive Quenching

205

PS

ED PS*

Catn

ED+

Oxidative Quenching Catn-1

PS-

PS+

Catn

ED Catn-1

PS

ED+

reactive excited state (PS*) follows either of two quenching phenomena, depending on the redox potential difference between the photosensitizer, and oxidation potential of the electron donor, or the reduction potential of the catalyst (Fig. 4) [55, 56]. In reductive quenching, the excited photosensitizer (PS*) is reduced by an electron donor (ED) to generate the reduced photosensitizer (PS− ) species. This PS− intermediate is a strong reducing agent and transfers an electron to the catalyst (Catn ) to generate the reduced catalytic species (Catn−1 ) and drive the catalytic cycle. On the contrary, during oxidative quenching, electron exchange occurs between the excited photosensitizer (PS*) and the catalyst (Catn ). Here, the reduced catalytic species (Catn−1 ) participates in the catalysis, whereas the oxidized photosensitizer (PS+ ) reverts back to the original photosensitizer via an electron transfer from the electron donor (ED). The light-absorbing component (photosensitizer) is one of the vital components in photocatalytic assembly. The ruthenium polypyridyl complexes, such as [Ru(bpy)3 ]2+ , are leading examples of widely explored photosensitizers for homogenous catalysis. [Ru(bpy)3 ]2+ achieves the excited state almost at unity following the photoirradiation, even at room temperature. Moreover, its excited state is longlived and varies from hundreds of nanoseconds to several microseconds, which ensures enough time for the intermolecular electron transfer process to compete with the intrinsic radiative and non-radiative relaxation processes [57]. Another popular photosensitizer is the iridium-based [Ir(ppy)2 (bpy)]+ complex. The lifetime of these Ru- and Ir-based complexes can be fine-tuned by introducing several other πinteracting chelating ligands. However, the low abundance of these metals increases the operational cost of photocatalytic hydrogen production. In an attempt to reduce that cost, several first-row transition metal-based complexes were also explored as photosensitizers. In this regard, zinc (Zn)- and copper (Cu)-based porphyrin complexes are worth of mentioning. In addition, a range of organic dye molecules, such as fluorescein, eosin-Y, and xanthene, have also been deployed. However, their low photostability during long exposure has severely impeded their practical applications. Recently, semiconductor materials, such as CdSe-quantum dot and nano-TiO2 , have found initial attention from the scientific community [58–60]. In a separate research direction, the photo-harvesting properties of durable plasmonic materials

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Redox Potential (V vs. SHE)

+

1

1.45 E0(2-*/3-)

0.31

Fc+/Fc E0(3+/2+*)

0.23

E0(HA+/A2+)

-0.5 E0(+*/0)

-1.22 E0(2+/+)

[Ru(bpy)3]2+

1.14 0.43

E0(+*/0)

-0.62 -1

1.42 E0(2-*/3-)

E0(4+*/3+)

E0(2+*/+) 0.028

0

1.18

1.08

Triethyl amine

Flourescene

[Zn(TMPP)]+

[Ir(ppy)2(bpy)3]2

-1.5 E0(2+/+)

[Cu(dbtmp)2]+

E0(1+/0)

E0(1+/0)

-0.4 E0(5+/4+*)

-1.35 E0(1-/2-*) Eosin Y

-1.36 E0(1-/2-*)

Ascorbic acid

Triethanol amine

(bpy-bi pyridine), (PPY- phenyl pyridine), (dbtmp- ) (TMPP - mesotetrakis(N-methyl-4-pyridyl)porphrine; dbtmp = 2,9-di(n-butyl)-3,4,7,8-tetramethyl-1,10-phenanthroline)

Fig. 5 Redox potential values of selected photosensitizer and sacrificial electron donor molecules recorded in organic/aqueous medium. The red and blue traces represent the excited state reduction and oxidation potential states, respectively. The asterisk (*) indicates the excited state

have been explored. The wide absorbance spectra of these materials ensure that photocatalytic hydrogen production can be activated by visible and NIR-portion of the sunlight [61–63]. The presence of the sacrificial electron donor is also important for the proper functioning of a photocatalytic assembly. Triethylamine (TEA), N, N’-dimethylp-toluidine (DMT), triethanolamine (TEOA), and ascorbic acid are the leading choices for the role of sacrificial electron donor. The electron donor typically undergoes oxidation and releases a proton during photocatalysis to support the protoncoupled electron transfer (PCET) step. Here, the redox potential of the electron donor and catalyst has to be within a feasible range of the redox potential of the excited photosensitizer to ensure a thermodynamically favored photocatalytic reaction. Figure 5 highlights the relative positioning of the redox potential values of the leading photosensitizers and their sacrificial electron donor counterparts. Several first-row transition metal-based catalysts have been used for the photochemical HER to date. However, only a few examples of homogenous catalysts are known for performing this activity in an aqueous solution [64]. Among all other molecular complexes, cobaloxime was one of the most explored templates that have been extensively utilized for photochemical HER. Initially, photocatalytic hybrid assemblies were prepared by combining cobaloximes with appropriate inorganic and organic photosensitizers. The integration of inorganic ([Ru(bpy)3 ]2+ and [Ir(ppy)2 (bpy)]+ ) and cobaloxime core displayed significant photocatalytic HER at a moderate rate. Alternatively, Zn- and Mn-based porphyrin complexes were also utilized as photosensitizer and incorporated axially into the cobaloxime core. Both complexes were employed for photochemical HER, where the Zn–porphyrin appended cobaloxime demonstrated relatively superior photocatalytic hydrogen production [65]. In recent years, several other inexpensive and synthetically less challenging photosensitizer alternatives based on aluminum, tin, and copper have been

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explored [66]. All the cobaloxime hybrid complexes were found to be active initially; however, they suffer from long-term instability under photocatalytic conditions. Eisenberg and group have synthesized the initial examples of a cobaloxime hybrid complex with amido-fluorescein, which was attached to the cobaloxime core through the axial position. The resultant hybrid complex showed three folds higher activity when compared to the untethered photosensitizer [57]. This result showcases the importance of a direct link between the photosensitizer and the catalyst. Taking inspiration from this work, our group has also developed one cobaloxime hybrid complex with a stilbene-based organic dye with an analogous linkage strategy. The complex was also found to be very active for photochemical hydrogen evolution, perform the reaction even in the presence of natural sunlight, and utilize neutral water as a proton source [67]. However, the long-term stability of the complex remains questionable during the catalytic process. Later, we extensively synthesized an array of cobaloxime derivatives with divergent inclusions at the axial position and probed these complexes for the photocatalytic HER. We found that all the complexes containing peripheral proton-exchanging groups remain fairly stable in an aqueous medium and show better photocatalytic activity than previously reported cobaloximes. We have incorporated several amine functionalities in its outer coordination sphere (OCS), and it has been observed that peripheral primary amines show higher activity than secondary amines [43]. We have also attempted to introduce imidazole-linked cobaloxime complexes for performing photocatalytic HER in aqueous conditions. These imidazole-containing cobaloximes exhibit higher hydrogen production under photoirradiation than previously mentioned pyridine-bound cobaloximes, which display only moderate HER [42]. The imidazole-linked complexes achieve a TON value of ~1200 in 100% aqueous conditions. This is one of the best-reported TON values achieved for a cobaloxime complex to date. The introduction of vitamin B6 molecules in the periphery of the cobaloxime core illustrated similar trends, as these complexes exhibit moderate photocatalytic hydrogen production and achieve a TON value of 132 [47]. These sets of cobaloximes represent a genre of all-weather ready hydrogen production catalysts, as they are operational in the presence of atmospheric oxygen and natural sunlight. Hence, these catalysts have the potential to be an integral part of the future photoreactors for industrial-scale hydrogen production.

5 Biological Hydrogen Production Biology has evolved hydrogenase enzymes that ensure an H2 -driven metabolism that was occurring even before the advent of photosynthesis [68]. Hence, biological hydrogen production can provide a unique way for carbon–neutral and sustainable energy harvesting. Three processes, namely photosynthesis, fermentation, and microbial electrolysis, can work in tandem to produce biological hydrogen [69, 70]. Naturally occurring and genetically modified microbes can use protons (H+ ) as an electron sink to produce H2 at the terminal end of a biological energy transduction

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process. Since H2 is not very soluble in water, it can be readily extracted from the water in its gaseous form. Despite the promises, a number of pragmatic factors, including the operational cost, the maintenance of experimental conditions, and the planning of large-scale microbial photoreactors, have seriously limited their practical applications [71–73].

6 Conclusion Hydrogen is a clean energy carrier and can be generated from sources ranging from fossil fuels (such as methane, coal, and oil) to sustainable water. The highly abundant and omnipresent water offers eco-friendly pathways for hydrogen production that can be directly linked to renewable energy resources. This reaction can be regulated with the direct use of renewable (sunlight) or renewable-derived electricity. Hence, both electrochemical and photochemical pathways for hydrogen production become critical in our pursuit of a greener future energy landscape. In this chapter, we have depicted a genre of cobalt-base homogeneous catalysts which can produce hydrogen at an efficient rate from water both electrochemically as well as photochemically. The natural abundance of the precursor materials and the ease of synthesis of these catalysts, along with their inherent oxygen and aquo-tolerance, make them prime candidates for the establishment of efficient hydrogen production unit development. Acknowledgements The authors would like to thank the support provided by the Indian Institute of Technology Bombay (IITB). The authors would like to thank the support provided by the Department of Science and Technology, Science and Engineering Research Board (DST-SERB), India for the core research grant (CRG/2020/001239) and DST, India-supported National Center of Excellence (DST/TMD/CCUS/CoE/202/IITB).

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Hydrogen Production from Liquid Hydrogen Carriers Sanjay Kumar Singh

Abstract Considering the ever-increasing carbon emission and its severe consequences on the global temperature, it is essential to explore sustainable energy resources with minimal or zero-carbon footprint. In this regard, hydrogen has emerged as a promising sustainable candidate to meet the global energy demand, primarily because it has high energy density and produces only water/water vapor upon usage in the fuel cell or combustion. However, sustainable production, safe storage, and transportation of hydrogen gas are challenging. Therefore, several hydrogen storage materials/carriers have been explored to store high gravimetric and volumetric hydrogen content and release and store hydrogen gas on demand. In this regard, being liquid at room temperature, the liquid hydrogen carriers offer the additional advantage of easy and safe storage, transportation, and dispensing. Further, these liquid hydrogen carriers contain high H2 content, which can be released on demand. Moreover, most liquid hydrogen carriers can also be regenerated from CO2 and biomass waste. Therefore, it is worth highlighting the potential of these liquid hydrogen carriers as promising candidates for hydrogen storage and production in a sustainable way. Learning objectives: • Insights about liquid hydrogen carriers (LHCs) • Generating different LHCs for hydrogen economy • Potential of LHCs for storage of hydrogen energy in transport application Keywords Liquid hydrogen carriers · Hydrogen storage · Hydrogen production · Catalytic processes

S. K. Singh (B) Catalysis Group, Department of Chemistry, Indian Institute of Technology Indore, Simrol, Khandwa Road, Indore, M.P. 453552, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 M. Goel and G. Sen (eds.), Climate Action and Hydrogen Economy, Green Energy and Technology, https://doi.org/10.1007/978-981-99-6237-2_13

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Abbreviations CO2 COP26: DoE HCNG IPCC LOHCs MOFs UNFCCC XPS

Carbon Dioxide 26Th Conference of the Parties Department of Energy, USA Hydrogen-enriched compressed natural gas Intergovernmental Panel On Climate Change Liquid Organic Hydrogen Carriers Metal–Organic Frameworks United Nations Framework Convention on Climate Change X-ray photoelectron spectroscopy

1 Introduction The ever-increasing greenhouse gases (CO2 and others) due to the excessive usage of fossil fuels to cater to the global energy demand resulted in an increase in Earth’s temperature at an alarming rate [1]. Therefore, it is challenging and essential to explore efficient and sustainable sources for meeting the energy demand of the current and future generations. The intergovernmental panel on climate change (IPCC), a United Nations body for assessing the science related to climate change, in the 26th Conference of the Parties (COP26) of the United Nations Framework Convention on Climate Change (UNFCCC) in Glasgow (2021) highlighted that it is the collective challenge for all nations on this planet to work together for taking effective steps to tackle the issues related to climate change [2]. It is evident that human intervention is the main cause of climate change, and the effect of climate change is now widespread, rapid, and becoming more intense, affecting every living thing in the world. It is predicted that the global temperature will rise by 1.5 to 2 °C during this century; hence, immediate efforts are required to reduce greenhouse gas (CO2 ) emissions on a large scale (Fig. 1)[3]. Notably, India is considered the third largest CO2 emission country in the world after China and USA, which produced over 2.4 giga tons of CO2 emission in 2020 [4]. At the COP26 meeting, India declared its responsible move to attain net zero emissions by 2070 [5]. In this regard, India has taken strong steps to draw 50% of its consumed energy from renewable sources and cut its carbon emissions by a billion tons by 2030. Appreciably, India announced the development of dense forest and tree cover in the country as a natural carbon sink capable of absorbing 2.5 to 3.0 billion metric tons of CO2 . One of the significant contributors to global CO2 emissions is transportation, which runs on petroleum-based fuels with IC engines [6]. However, the CO2 emission per person per kilometer traveled by public transport (such as train or bus) is essentially much less than those the personal vehicles (petrol-fueled cars). In the current global efforts to reduce the CO2 emission scenario, battery-based electric vehicles are

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Fig. 1 Global rise in CO2 emission and temperature (Reproduced with permission from Ref. 3) [3]

gaining much attention and are at the center stage. Indeed, battery-operated electric vehicles are considered pollution-free vehicles. The source of electricity required to charge battery-based electric vehicles significantly impacts the effective CO2 emission from electric vehicles. Notably, over 90% of electricity in India is produced from coal-based power plants with significantly high greenhouse gas emissions. Hence, the battery electric vehicles charged by the electricity produced from coal-based power plants have an effective CO2 emission as high as a petrol-fueled vehicle. Moreover, India has a limited lithium source required for Li-ion batteries production. Moreover, lithium and nickel required for batteries are extracted from open mines, causing excessive greenhouse emissions and deforestation. On the other hand, India is seriously working on decreasing its dependence on fossil fuels by exploring methanol (M15, 15% methanol) and ethanol (E5, 5% ethanol) blended petrol. Therefore, new, renewable, and sustainable alternative energy sources need to be explored to fuel transportation and others to meet global targets of net zero-carbon emission. Appreciable efforts have been made to establish solar and wind-based renewable energy to meet global energy demand. In this regard, India has established solar-driven power plants on a large scale; for instance, Asia’s largest 750 MW solar plant was established in Rewa, Madhya Pradesh. In this regard, the potential of hydrogen gas (H2 ) has been identified as an efficient, renewable, and sustainable fuel for the current and future generations. Hydrogen has a gravimetric energy density (120 MJ/kg) three times higher than fossil fuel (46 < J/kg). Moreover, hydrogen gas is also emission-free because it generates water vapor/water only when hydrogen gas is combined with oxygen in the fuel cell [7]. It is expected that hydrogen and fuel cell technologies may achieve a 33–35% reduction in greenhouse gases by 2030 from its 2005 level, apart from co-benefits in terms of lower levels of air pollution, affordability, and sustainable transportation. The concept of ‘hydrogen economy’ has three major components—hydrogen production, hydrogen storage, and utilization of hydrogen (Fig. 2). However, due to its physical and chemical properties, hydrogen gas production, storage, and transportation become challenging [8]. For instance, over 11,000 L tanks will be required to run

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Fig. 2 Schematic representation of hydrogen storage, production, and application

a hydrogen-fueled vehicle for 100 km. Therefore, hydrogen is stored at high pressure (330 and 750 bar) which is specially designed tanks for hydrogen-fueled electric vehicles. Hydrogen is also being liquified under cryogenic conditions (−252.87 °C at 1.013 bar) for transportation, but leakage and evaporation of hydrogen gas cause serious safety concerns. Storage of hydrogen in metal hydrides or metal–organic frameworks (MOFs) as solid-state storage is also considered a promising development toward the safe storage and supply of hydrogen gas for usage [9, 10]. Despite that, all these storage technologies exhibited promising ways for hydrogen storage for safe transport and utilization, these processes suffer from several drawbacks, such as the energy-intensive process to liquefy hydrogen gas at −252.87 °C, or low effective wt% of hydrogen in solid storage, and so on. Nevertheless, a significant process has been marked in developing hydrogenfueled vehicles at the global level. For instance, Toyota (Mirai), Honda, and Hyundai (Nexo) manufactured hydrogen cars having a mileage equivalent to a typical petrolbased car [11]. Advantageously, hydrogen-fueled buses can run 300–450 km without refilling. Moreover, the hydrogen fuel refilling time is equivalent to a petrol-fueled car. However, the high cost with poor infrastructure for refueling hydrogen-fueled vehicles is a major bottleneck that must be resolved to make hydrogen-fueled vehicles a reality for common people. The global hydrogen station deployment forecast is that over 1600 hydrogen stations will be deployed in Asia pacific (including India) by 2032, which is at par with the projections for Europe and America [12]. Worldwide hydrogen-fueled vehicles are serving in almost all sectors, including personal cars, trains, metro, airplanes, heavy-duty trucks, and so on, which essentially highlights the technological maturity in the field of hydrogen-fueled vehicles. India is also actively progressing in establishing a hydrogen-based economy and recently launched the National Hydrogen Mission, which encouraged the researchers and industries in India to develop indigenous technologies and consider hydrogen a clean energy

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source to meet industrial energy demand. Hydrogen blended CNG (H-CNG) is one of the promising progress toward a clean energy source, where bending 18–23% hydrogen gas in CNG (H-CNG) can reduce carbon monoxide emission by 70% and greenhouse gas emission by 15–20%, with only minor modifications in existing CNG vehicles [13]. This encouraging progress toward hydrogen (production, storage, and utilization) suggests that global hydrogen demand is expected to escalate in all sectors by the coming 2–3 decades [14]. However, 40% selectivity toward hydrogen from hydrazine decomposition in water at room temperature. Moreover, by decreasing the particle size from 16 to 5 nm for Rh catalysts, a threefold enhancement in the activity was observed. 15 N NMR of the reaction aliquot of the hydrazine decomposition reaction over Rh catalyst inferred a gradual decrease in the peak corresponding to hydrazine (−330 ppm) with a gradual increase in the peak at −375 ppm corresponding to ammonia with the progress of

N2H3* H*

NH2*

H*

NH* H*

N2H3*

N*

NH2* NH *

N2

NH2* 1/3N2 + 4/3NH3

H*

H2

HN=NH

H*

H2

N2H*

H*

2

NH3

H2NNH2

H2NNH2

N2 H2NNH2

N2 + 2H2

Fig. 4 Reaction pathway for hydrogen production from hydrazine (Reproduced with permission from Ref. 28 ) [28]

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the reaction, suggesting that complete decomposition of hydrazine to hydrogen was not achieved over Rh catalyst. The literature revealed that the electronic and geometric structures of the catalyst can be fine-tuned by the addition of a second component (such as in alloy or core–shell catalysts), and hence enhancement in the catalytic activity and product selectivity can be achieved [29]. At the nanoscale level, the effect of these factors is more pronounced, where heterogeneity in the metal–metal interactions in the bi/multimetallic catalysts resulted in better interaction and activation of bonds of the reactants and stabilization of reaction intermediates on the catalyst surface. These factors may contribute to enhanced catalytic activity and tuned product selectivity observed for bi/multi-metallic catalysts as compared to the corresponding monometallic catalysts [29]. While exploring several bimetallic alloy catalysts of Ni with Rh, Pt, Pd, and Fe, we achieved complete and selective decomposition of hydrazine to hydrogen gas in water at room temperature (Ni-Rh, Ni-Pt). Compared to the 43% hydrogen selectivity observed with Rh catalyst, alloying Ni with Rh in varying Ni/Rh molar ratio, we observed that Ni/Rh ratio of 1:4 complete decomposition of hydrazine with 100% selectivity for hydrogen gas was achieved at room temperature [30]. Noticeably, a shift in the PXRD peaks of Ni-Rh catalysts to a lower angle compared to that of Ni catalyst was observed, which is consistent with the alloy formation with the incorporation of larger Rh atoms in the place of smaller Ni atoms causing lattice expansion. X-ray photoelectron spectroscopic (XPS) results also inferred the corresponding shifting in the peaks corresponding to Ni and Rh due to charge transfer between the closely interacting Ni and Rh atoms in the Ni-Rh alloy catalyst. Analogously, Ni-Pt alloy catalysts with varying Pt contents (7–31 mol%) exhibited complete decomposition of hydrazine with 100% selectivity for hydrogen. This is noteworthy to mention that both monometallic Ni and Pt catalysts are inactive for the decomposition of hydrazine at room temperature. XPS analysis of Ni-Pt catalyst confirms the alloy composition, and hence the involvement of the bimetallic Ni-Pt alloy phase on the catalyst surface and the synergistic interaction of Ni and Pt facilitated the observed high catalytic activity for Ni-Pt catalyst [31] Analogously, Ni-Ir catalysts with 5–10 mol% Ir content exhibited 100% selectivity for hydrogen from hydrazine decomposition at room temperature, while the monometallic Ni is inactive, and the monometallic Ir shows only 7% selectivity for hydrogen. XPS spectra of the Ni–Ir nanoparticles indicate the co-existence of both Ir and Ni in alloy form, as the peaks corresponding to Ir[4f7/2 ] shifted toward higher binding energies relative to that for the monometallic Ir, while those of Ni[2p3/2 ] toward lower binding energies. Along with the well-explored heterogeneous catalysts, hydrogen production from hydrazine using homogeneous catalyst are also explored [32]. For instance, hydrazine coordinated complexes of Fe, W, Mo, Ir, and Ru resembles the reaction intermediates of nitrogen to ammonia reduction and hydrogen production from hydrazine, and hence these systems can be explored as potential catalytic candidates [32, 33]. We explored arene-Ru(II)-Nhydroxy-iminopyridine complex [(η6 -C6 H6 )Ru(κ 2 -N-hydroxy-iminopyridine)Cl]+ for the catalytic dehydrogenation of hydrazine in tetrahydrofuran, where the iminopyridine ligand played a crucial role tuning the catalytic activity for hydrogen

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production from hydrazine [34]. The enhanced activity of the catalyst can be attributed to the possible involvement of the hydroxyl group of N-hydroxyiminopyridine ligand with hydrazine coordinated to the ruthenium center. NMR and mass investigations revealed the presence of end-on coordinated hydrazine Ru(II)arene intermediate [(η6 -C6 H6 )Ru(κ 2 -L1)(κ 1 -NH2 NH2 )]+ , where the coordination of hydrazine to Ru center and subsequent activation of hydrazine (Ea = 57.9 kJmol−1 ) are expected to be the key steps involved in achieving dehydrogenation of hydrazine. Advantageously, the studied molecular catalyst can be recycled for six consecutive catalytic runs of hydrazine dehydrogenation.

2.2 Formic Acid Formic acid is a colorless liquid with a strong odor at room temperature, but its low toxicity and its liquid nature make its storage, handling, and transportation [35]. Advantageously, formic acid has a hydrogen storage capacity of 4.4 wt. %. Notably, the dehydrogenation of formic acid released an equimolar ratio of H2 and CO2 in a thermodynamically favorable (ΔG° = −32.9 kJ mol−1 ) process at room temperature, but this process is kinetically not favored. The addition of a base may help in increasing the reaction kinetics by the formation of formate. However, along with the formic acid dehydrogenation pathway to H2 and CO2 , the dehydration of formic acid to water and the poisonous CO gas is also thermodynamically feasible, and hence new and efficient catalytic processes for selective generation of hydrogen from formic acid needs to be developed [36]. In this regard, literature revealed a variety of efficient catalysts had been explored for formic acid dehydrogenation. Typically, hydrogen production from formic acid involves three primary paths (Fig. 5): (i) generation of a formato complex by the reaction of the active form of the catalyst and formate anion (ii) decarboxylation of the formato complex to generate a metal hydride species, and (iii) proton-assisted hydrogen release from the metal hydride complex to regenerate the active catalytic species. A wide range of catalytic systems explored for hydrogen production from formic acid. It is observed that the presence of a vacant coordination site at the metal center and the facile protonation–deprotonation properties of the ligand played a significant role in achieving high catalytic activity for the dehydrogenation reaction. In this regard, we employed several arene-Ru(II) complexes containing N,O donor bidentate ligands for the catalytic dehydrogenation of formic acid in water (Fig. 5) [37]. Results inferred that the complex [(η6 -C10 H14 )Ru(κ 2 -Npy OH-L)Cl]+ (L = pyridine-2-ylmethanol) displayed high activity as compared to the others to achieve an initial TOF of 1548 h−1 . Moreover, the studied catalyst displayed very high stability in water with a turnover number of 6050 over seven consecutive catalytic runs. The higher activity of the studied arene-Ru catalysts can be attributed to the involvement of the oxygen atom of pyridine-2-ylmethanol in a facile protonation– deprotonation step during the dehydrogenation process. Extensive mass, NMR, and kinetic investigations evidenced the formation of several intermediate species, such

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S. K. Singh catalyst sodium formate water, 90 °C

Turnover frequency (TOF)

HCOOH

H2 + CO2

Step (i)

Step (iii)

Step (ii)

Arene-Ru catalysts

Fig. 5 Catalytic route for hydrogen production from formic acid (Reproduced with permission from Ref. 37) [37]

as the diruthenium species [{(η6 -C10 H14 )Ru(κ 2 -N,O-μ-O-L}2 ]2+ , the formate coordinated species [(η6 -C10 H14 )Ru(κ 2 -Npy O-L)(HCO2 )] and the Ru-hydride species [(η6 -C10 H14 )Ru(κ 2 -Npy O-L)(H)] formed during the catalytic dehydrogenation of formic acid over the active catalyst.

2.3 Formaldehyde Formaldehyde (CH2 O) is a C1-based liquid organic hydrogen carrier (LOHC) having 8.2 wt% H2 , and even the common aqueous formaldehyde also has a very high hydrogen content of 5.0 wt% [38]. Several catalytic systems have been lately explored for hydrogen production from formaldehyde. The dehydrogenation of formaldehyde primarily involves several steps: initially, the formaldehyde, in the presence of a water molecule, gem diol, while further dehydrogenate to formic acid with the release of one molecule of hydrogen gas, and finally, dehydrogenation of formic acid releases another molecule of hydrogen gas with CO2 . Firstly, Prechtl et al. reported an areneRu(II) complex ([(η6 -C10 H14 )RuCl2 ]2 ) for H2 production from aqueous formaldehyde solution (turnover number of 700) in water at 95 °C [39]. Recently, we explored in situ generated arene-Ru(II)-imidazole complexes for hydrogen generation from formaldehyde in water-based reaction at 95 °C, while screening various mono-dentate nitrogen-based ligands [40]. In comparison to the ligand-free reaction where 242 mL of gas was generated from 1.07 mL of aq. formaldehyde at 95 °C, the volume of the gas released to 328 mL for the analogous reaction performed in the presence of imidazole as an additive (Fig. 6). Moreover, the developed catalytic system can produce hydrogen from formaldehyde in the absence of an external base and works effectively at 95 °C in water with an appreciably turnover number (>12,000) and TOF

Hydrogen Production from Liquid Hydrogen Carriers

223

(b)

(a) Volume of gas (mL)

400 300 200 L6 (1 equiv.) L6 (2 equiv.) L6 (3 equiv.)

100 0

0

100

200 300 Time (min)

400

Fig. 6 Effect of imidazole ligand and the reaction pathway for hydrogen production from formaldehyde over arene-Ru(II)-imidazole (Reproduced with permission from Ref. 40) [40]

(5175 h−1 ) for long-term bulk hydrogen production over ruthenium-imidazole catalyst. Further, we have also performed mass and NMR analysis of the reaction mixture and reported a plausible reaction pathway for the dehydrogenation of formaldehyde over an imidazole-based complex. Firstly, Ru-methanediol species is generated upon the coordination of methanediol, from the active catalytic species. Subsequently, by releasing one equivalent of H2 (via a Ru–H intermediate), a ruthenium-formate species was generated. Further, the Ru-formate species undergoes decarboxylation to produce a Ru–H species, followed by the generation of a second H2 molecule with the aid of imidazole ligand and regenerates the active catalytic species.

2.4 Methanol Methanol is the simplest alcohol with only one carbon, low volatility, and liquid under ambient condition with good miscibility in water. Notably, methanol has a hydrogen content of 12.5%, which can be produced as three molecules of hydrogen along with one molecule of carbon dioxide from one molecule of methanol in water [41]. Further, methanol can also be synthesized from biomass/food waste and by CO2 hydrogenation [42]. Hydrogen production from methanol in the presence of water takes place via three steps (1) initially, with the release of one molecule of hydrogen gas methanol transformed to formaldehyde, (2) further, the produced formaldehyde molecule reacts with water to form methanediol, which undergoes dehydrogenation to produce the second molecule of hydrogen gas and formic acid, (3) at the last step, formic acid undergoes dehydrogenation to produce the third molecule of hydrogen gas and one molecule of carbon dioxide (Table 2) [41]. So, essentially, formaldehyde and formic acid are the intermediates formed during hydrogen production from methanol (Table 2).

LOHCs

CH3 OH

HCHO

HCOOH

S. no

1

2

3

12.5 8.4 4.3

HCHO (g) + H2 O (l) → CO2 (g) + 2H2 (g)

HCOOH (l) → CO2 (g) + H2 (g)

8.0

CH3 OH (l) + H2 O (l) → HCOOH (l) + 2H2 (g)

CH3 OH (l) + H2 O (l) → CO2 (g) + 3H2 (g)

6.25

wt%

CH3 OH (l) → HCHO (g) + H2 (g)

Reaction equation

31.6

−30.7

130.7

–

129.8

ΔH°298 (kJ.mol−1 )

Table 2 Hydrogen production pathway from the methanol–water in the presence of a suitable catalyst

−31.8

−22.8

8.9

–

63.5

ΔG°298 (kJ.mol−1 )

224 S. K. Singh

Hydrogen Production from Liquid Hydrogen Carriers

225

n(H2)/n(CH3OH)

1 0.8 0.6 0.4 0.2 0

Catalysts

Fig. 7 Hydrogen production from methanol over ruthenium catalyst

Notably, thermodynamics of various reaction steps involved in methanol dehydrogenation inferred that the production of hydrogen gas from methanol and formic acid is an endothermic process, while that from formaldehyde is an exothermic process [43]. Advantageously, CO2 /bicarbonate (the byproduct of methanol dehydrogenation) can further be hydrogenated to methanol, formaldehyde, and formic acid, and hence these C1-based liquid hydrogen carriers can act as a net zero-carbon emission system for hydrogen production [42, 43] Notably, methanol reforming at 200–350 °C can produce hydrogen gas, whereas utilizing a suitable catalyst may not only bring down the reaction temperature < 200 °C but also tune the selectivity toward hydrogen gas. We explored ruthenium nanoparticle-based catalysts for hydrogen production from methanol at a temperature as low as 110 °C in water [44]. Notably, performing the reaction in the presence of 2-hydroxy pyridine ligand further improved the yield of hydrogen gas to 0.8 mol of hydrogen gas per mol of methanol. Moreover, X-ray photoelectron spectroscopy results also inferred the incorporation and hence the involvement of the 2-hydroxy pyridine ligand in the catalytic hydrogen production from methanol over ruthenium catalyst. The presence of purified hydrogen gas only in the fluent of the catalytic reaction and formate in the reaction solution at the end of the reaction inferred that in the studied system using ruthenium catalyst, hydrogen gas was selectively produced with no emission of CO2 gas from methanol (Fig. 7).

2.5 Glycerol Glycerol, a crude byproduct of biodiesel (constitutes 10 wt% of biodiesel) and an important product of biomass, can be explored as a potential source for hydrogen production, as it is a high boiling liquid, non-flammable and non-toxic [45, 46] Notably, global biodiesel production is increasing every year (estimated to increase

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S. K. Singh

3CO2 + 7H2

...(1)

C3H6O3 + H2 Lactic Acid C3H6O3 + H2 Glyceraldehyde HCOOH + C2H4O3 + 2H2

...(2)

C2H4O3 + H2O

2HCOOH + H2

...(5)

C3H8O3 + H2O

3HCOOH +4H2

...(6)

C3H8O2

...(7)

C3H8O3 + 3H2O C3H8O3 C3H 8O 3 C3H6O3 + 2H2O

C3H4O2 + 2H2

...(3) ...(4)

Scheme 1 Key reactions involved in hydrogen production from glycerol

to 46 billion L by 2025), and hence glycerol production is also expected to increase [47]. Notably, glycerol to H2 gas production involves several key reaction steps (Scheme. 1), leading to the generation of several intermediate products (such as glyceraldehyde and lactic acid), which may further decompose to H2 gas during the process. Aqueous-phase reforming (APR) process involves C–C cleavage followed by a water gas shift reaction favors at low temperature. Industrially, hydrogen gas is being produced from glycerol via steam and aqueousphase reforming (APR) at higher temperature (>200 °C). Therefore, it is important to develop a sustainable process for the selective production of hydrogen gas from glycerol at low temperature. In this regard, we demonstrated that selective production of hydrogen gas can be achieved from glycerol over the ruthenium catalyst in the presence of NaOH in water at 90–120 °C [48]. Results inferred that the role of base and water is crucial in achieving higher H2 selectivity. Through our developed process, hydrogen gas content as high as 11 mmol (1.61 equiv. H2 per mol of glycerol) with >99% conv. of glycerol was achieved over the ruthenium catalyst, along with a high lactic acid yield (70%) (Fig. 8). Moreover, the developed process works well even for the bulk production of H2 gas from glycerol with ca. 70 L H2 produced per gram of Ru with the H2 yield of 350 L per L of glycerol for over 36 h, which inferred the high long-term stability of the ruthenium catalyst. We estimated that 1 kg of hydrogen gas can be produced from 52 L of glycerol over the developed protocol using a ruthenium catalyst at 110 °C.

Hydrogen Production from Liquid Hydrogen Carriers

227

H2

Volume of Gas (mL)

200

+

glycerol

160 120 80

poly(lactic acid) (PLA) a biodegradable polymer

40 0

0

100 200 300 400 500 600 Time (min)

Fig. 8 Hydrogen production from glycerol over ruthenium catalyst at 110 °C

3 Conclusion Hydrogen is indeed a promising candidate with the potential to meet the global energy demand in a sustainable way by mitigating carbon emissions. However, in this process, the focus should also be on the sustainable process of hydrogen production. Liquid hydrogen carriers with zero-carbon (hydrazine and ammonia), C1-based candidates (methanol, formaldehyde, formic acid), or biomass-derived candidates (glycerol, ethanol, and others) have shown potential to produce hydrogen gas with zero or low carbon footprint. Compared to the traditional high-temperature reforming processes, catalytic routes for hydrogen production provide an alternative pathway to produce blue/green hydrogen gas with reduced net carbon emission. The developed processes highlight that high hydrogen content can be extracted from these liquid hydrogen carriers under the relatively mild condition with high purity of hydrogen gas. Acknowledgements Author acknowledges the funding support from SERB, CSIR, and IIT Indore under various research programs. Support of all the research students of the catalysis group at IIT Indore is highly appreciated.

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Solid Oxide Electrolysis Cell for Hydrogen Generation: General Perspective and Mechanism Subhrajyoti Ghosh and Suddhasatwa Basu

Abstract Low-temperature electrochemical hydrogen production process, such as proton-exchange membrane electrolyzer and alkaline electrolyzer, uses expensive noble metal catalysts and requires higher electrical energy for water oxidation. A solid oxide electrolysis cell (SOEC) operating at a higher temperature provides a highly energy-efficient and cost-effective route of hydrogen production with comparatively less electricity consumption. Moreover, the use of less expensive ceramic electrolytes and electrodes has added a value to its application. Proton (H+ )-conducting solid oxide cell (H-SOEC) provides the scope of dry and pure hydrogen production at reduced temperature (