Carbon Dioxide Reduction through Advanced Conversion and Utilization Technologies 9781138095298, 113809529X, 9781315104171

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Carbon Dioxide Reduction through Advanced Conversion and Utilization Technologies

Electrochemical Energy Storage and Conversion Series Editor: Jiujun Zhang National Research Council Institute for Fuel Cell Innovation Vancouver, British Columbia, Canada Recently Published Titles Graphene: Energy Storage and Conversion Applications Zhaoping Liu and Xufeng Zhou Lithium-Ion Batteries: Fundamentals and Applications Yuping Wu Lead-Acid Battery Technologies: Fundamentals, Materials, and Applications Joey Jung, Lei Zhang, and Jiujun Zhang Solar Energy Conversion and Storage: Photochemical Modes Suresh C. Ameta and Rakshit Ameta Electrolytes for Electrochemical Supercapacitors Cheng Zhong, Yida Deng, Wenbin Hu, Daoming Sun, Xiaopeng Han, Jinli Qiao, and Jiujun Zhang Electrochemical Reduction of Carbon Dioxide: Fundamentals and Technologies Jinli Qiao, Yuyu Liu, and Jiujun Zhang Metal–Air and Metal–Sulfur Batteries: Fundamentals and Applications Vladimir Neburchilov and Jiujun Zhang Photochemical Water Splitting: Materials and Applications Neelu Chouhan, Ru-Shi Liu, and Jiujun Zhang Electrochemical Supercapacitors for Energy Storage and Delivery: Fundamentals and Applications Aiping Yu, Victor Chabot, and Jiujun Zhang Electrochemical Polymer Electrolyte Membranes Jianhua Fang, Jinli Qiao, David P. Wilkinson, and Jiujun Zhang Electrochemical Energy: Advanced Materials and Technologies Pei Kang Shen, Chao-Yang Wang, San Ping Jiang, Xueliang Sun, and Jiujun Zhang High-Temperature Electrochemical Energy Conversion and Storage: Fundamentals and Applications Yixiang Shi, Ningsheng Cai, and Jiujun Zhang Redox Flow Batteries: Fundamentals and Applications Huamin Zhang, Xianfeng Li, and Jiujun Zhang Carbon Nanomaterials for Electrochemical Energy Technologies: Fundamentals and Applications Shuhui Sun, Xueliang Sun, Zhongwei Chen, Jinli Qiao, David P. Wilkinson, and Jiujun Zhang Proton Exchange Membrane Fuel Cells Zhigang Qi Hydrothermal Reduction of Carbon Dioxide to Low-Carbon Fuels Fangming Jin Lithium-Ion Supercapacitors: Fundamentals and Energy Applications Lei Zhang, David P. Wilkinson, Zhongwei Chen, Jiujun Zhang Advanced Bifunctional Electrochemical Catalysts for Metal-Air Batteries Yan-Jie Wang, Rusheng Yuan, Anna Ignaszak, David P. Wilkinson, Jiujun Zhang Carbon Dioxide Reduction through Advanced Conversion and Utilization Technologies Yun Zheng, Bo Yu, Jianchen Wang, Jiujun Zhang https://www.crcpress.com/Electrochemical-Energy-Storage-and-Conversion/book-series/ CRCELEENESTO

Carbon Dioxide Reduction through Advanced Conversion and Utilization Technologies

Yun Zheng Bo Yu Jianchen Wang Jiujun Zhang

CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2019 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Printed on acid-free paper International Standard Book Number-13: 978-1-138-09529-8 (Hardback) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright. com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data Names: Zheng, Yun (Chemical engineer), author. Title: Carbon dioxide reduction through advanced conversion and utilization technologies / Yun Zheng, Bo Yu, Jianchen Wang, Jiujun Zhang. Description: Boca Raton : Taylor & Francis, CRC Press, 2019. | Series: Electrochemical energy storage and conversion | Includes bibliographical references and index. Identifiers: LCCN 2018057440| ISBN 9781138095298 (hardback : alk. paper) | ISBN 9781315104171 (ebook) Subjects: LCSH: Carbon dioxide--Separation. | Electrolytic reduction. | Carbon dioxide--Recycling. Classification: LCC TP244.C1 Z44 2019 | DDC 660.028/6--dc23 LC record available at https://lccn.loc.gov/2018057440 Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com

Contents Preface.......................................................................................................................xi Acknowledgments................................................................................................... xiii Authors...................................................................................................................... xv Chapter 1 Introduction to CO2 Reduction through Advanced Conversion and Utilization Technologies.................................................................1 1.1 Globe Energy Status, Challenges, and Perspectives.................... 1 1.2 CO2 Emission and Reducing........................................................2 1.3 Main Approaches of CO2 Conversion and Utilization.................4 References.............................................................................................6 Chapter 2 Fundamentals of CO2 Structure, Thermodynamics, and Kinetics........9 2.1 Molecular Structure of CO2.........................................................9 2.2 Thermodynamics of CO2.............................................................9 2.3 Kinetics of CO2 Conversion....................................................... 14 2.4 Summary.................................................................................... 16 References........................................................................................... 16 Chapter 3 Enzymatic and Mineralized Conversion Process of CO2 Conversion....................................................................................... 19 3.1 Enzymatic Conversion of CO2................................................... 19 3.2 Mineralization Process of CO2 Conversion............................... 22 3.3 Summary....................................................................................26 References........................................................................................... 27 Chapter 4 Thermochemical and Photochemical/Photoelectrochemical Conversion Process of CO2 Conversion.............................................. 31 4.1 Thermochemical Process of CO2 Conversion............................ 31 4.1.1 CO2 Hydrogenation to CH3OH...................................... 31 4.1.2 CO2 Hydrogenation to HCOOH..................................... 33 4.1.3 CO2 (Dry) Reforming of Methane (DRM).................... 35 4.2 Photocatalytic and Photoelectrochemical Processes of CO2 Conversion������������������������������������������������������������������������� 38 4.3 Summary.................................................................................... 42 References........................................................................................... 42

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Chapter 5 Low-Temperature Electrochemical Process of CO2 Conversion......... 49 5.1 Brief Introduction to the Electrochemical Process of CO2 Conversion.......................................................................... 49 5.2 Thermodynamics of Low-Temperature Electrochemical Process....................................................................................... 49 5.3 Electrolyzer Used in Low-Temperature Electrochemical Process....................................................................................... 51 5.4 Catalyst/Electrode Used in Low-Temperature Electrochemical Process............................................................ 51 5.5 Summary and Outlook............................................................... 55 References........................................................................................... 55 Chapter 6 High-Temperature Electrochemical Process of CO2 Conversion with SOCs 1: Introduction and Fundamentals.................................... 57 6.1 Introduction of Solid Oxide Cells (SOCs).................................. 57 6.2 Fundamentals of High-Temperature CO2 Conversion through Electrochemical Approaches��������������������������������������� 58 6.2.1 Thermodynamics of High-Temperature CO2/H2O Co-electrolysis................................................................ 58 6.2.2 Kinetics of High-Temperature CO2/H2O Co-electrolysis................................................................ 62 6.2.3 Comparisons between Water Electrolysis, CO2 Electrolysis, and H2O/CO2 Co-electrolysis�������������������64 6.2.4 Key Material Selection and Components of SOCs........64 6.3 Summary.................................................................................... 67 References........................................................................................... 67 Chapter 7 High-Temperature Electrochemical Process of CO2 Conversion with SOCs 2: Research Status............................................................. 71 7.1 Brief History.............................................................................. 71 7.2 Research Status of HTCE with SOC in the United States......... 74 7.3 HTCE Research towards Sustainable Hydrocarbon Fuels in Europe.................................................................................... 86 7.4 Research Status of HTCE with SOC in China.......................... 98 7.5 Summary.................................................................................. 103 References......................................................................................... 103 Chapter 8 High-Temperature Electrochemical Process of CO2 Conversion with SOCs 3: Key Materials.............................................................. 113 8.1 Materials and Microstructures of Electrodes........................... 113 8.2 Fuel Electrode Materials.......................................................... 114 8.3 Oxygen Electrode Materials.................................................... 119

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8.3.1  Reaction Mechanism of Oxygen Electrode Process...................................................................... 119 8.3.2  Mixed Ionic and Electronic Materials....................... 120 8.3.2.1 Perovskites (ABO3±δ)................................. 120 8.3.2.2 Double Perovskites (AA′B2O6−δ)................ 122 8.3.2.3 Ruddlesden-Popper (A2BO4+δ)................... 124 8.3.3  Main Issues of the Oxygen Electrode....................... 127 8.4 Electrolyte............................................................................. 128 8.5 Interconnect Materials.......................................................... 129 8.6 Cell Sealing Materials........................................................... 130 8.7 Summary............................................................................... 131 References........................................................................................ 132 Chapter 9

High-Temperature Electrochemical Process of CO2 Conversion with SOCs 4: Measurement, Characterization, and Simulation...... 139 9.1 9.2

Electrochemical Measurement.............................................. 139 Microstructure Characterization........................................... 141 9.2.1 SEM, TEM, and STEM............................................. 141 9.2.2 FIB-SEM and XCT................................................... 142 9.2.3 STM/STS and AFM.................................................. 144 9.3 Surface Analysis................................................................... 145 9.4 Simulation and Calculation Method..................................... 148 9.5 Product Analysis................................................................... 149 9.6 Summary............................................................................... 150 References........................................................................................ 150 Chapter 10 High-Temperature Electrochemical Process of CO2 Conversion with SOCs 5: Advanced Fabrication Methods (Infiltration and Freeze Casting)................................................................................ 155 10.1 Infiltration for Nano-Structured Ln1−xSrxMO3−δ (Ln=La, Sm; B=Mn, Co, Fe) SOC Electrode������������������������������������������������������������������������������ 155 10.1.1  Introduction of Infiltration Used in SOCs............... 155 10.1.2 Process of Infiltration.............................................. 156 10.1.3 Infiltration with Various Ln1−xSrxMO3−δ SOC Electrodes................................................................ 157 10.1.3.1 LSM-YSZ Electrode................................ 157 10.1.3.2 LSC-YSZ Electrode................................ 160 10.1.3.3 LSF-YSZ Electrode................................. 161 10.1.3.4 LSCF-YSZ Electrode.............................. 163 10.1.3.5 SSC-Infiltrated Electrodes...................... 164 10.1.3.6 Comparison of Infiltrated Electrodes’ Performance............................................ 165 10.1.4 Conclusions and Future Prospects.......................... 167

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10.2 An Electrolyte-Electrode Interface Structure with Directional Micro-Channel Fabricated by Freeze Casting���� 167 10.2.1 Freeze Casting Technology Used in SOCs............. 167 10.2.2 The Process and Critical Factors of Freeze Casting Technology................................................. 168 10.2.2.1 The Process of Freeze Casting................ 168 10.2.2.2 Effect of Critical Factors on Morphologies.......................................... 169 10.2.3 Summary and Perspectives..................................... 175 References......................................................................................... 177 Chapter 11 High-Temperature Electrochemical Process of CO2 Conversion with SOCs 6: Advanced Structure (Heterostructure)........................ 187 11.1 Brief Introduction for Heterostructure.................................. 187 11.2 Heterostructure of ABO3/A2BO4 in SOCs............................ 189 11.3 Mechanism of ORR/OER in ABO3/A2BO4 Heterostructure.... 192 11.3.1 Electronic Structure................................................ 192 11.3.2 Anisotropy............................................................... 194 11.3.3 Lattice Strain (or the Mismatch in Lattice Parameter)............................................................... 194 11.3.4 Cation Inter-diffusion.............................................. 195 11.4 Current Challenges for ABO3/A2BO4 Heterostructure......... 196 11.4.1 Barriers to Accurately Detecting the Performance of a Heterointerface........................... 197 11.4.2 Invisibility of Heterointerface and its Unclear Mechanism.............................................................. 197 11.4.3 The Gap Between Theoretical Investigation and Practical Application............................................... 198 References......................................................................................... 198 Chapter 12 High-Temperature Electrochemical Process of CO2 Conversion with SOCs 7: The Significant Phenomenon of Cation Segregation....... 203 12.1 Introduction of Cation Segregation in Perovskite-Based SOC Electrodes�������������������������������������������������������������������� 203 12.2 Characterization of Surface Segregation..............................204 12.2.1 Low-Energy Ion Scattering.....................................205 12.2.2 Auger Electron Spectroscopy and Scanning Electron Microscope...............................................207 12.2.3 X-Ray Photoelectron Spectroscopy.........................209 12.2.4 Scanning Transmission Electron Microscope and Energy-Dispersive X-Ray Spectroscopy��������� 210 12.2.5 Secondary Ion Mass Spectroscopy......................... 211 12.2.6 Atomic Force Microscope and Scanning Tunneling Microscope............................................. 211

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12.2.7 X-Ray Diffraction.................................................... 214 12.2.8 State-of-the-Art Characterization Methods for Surface Segregation������������������������������������������������ 215 12.2.8.1 In Situ XPS............................................. 215 12.2.8.2 Environmental Transmission Electron Microscopy............................... 216 12.2.8.3 In Situ SIMS........................................... 217 12.2.8.4 Resonant Soft X-Ray Reflectivity and Resonant Anomalous X-Ray Reflectivity��������������������������������������������� 218 12.2.8.5 Raman Spectroscopy and In Situ Raman Spectroscopy.............................. 218 12.2.8.6 In Situ X-Ray Fluorescence.................... 219 12.3 Factors Influencing Segregation Level in PerovskiteBased Oxides����������������������������������������������������������������������� 221 12.3.1 The Effect of Cation Non-Stoichiometry................ 221 12.3.2 The Effect of the Cation Species............................. 223 12.3.3 The Effect of Crystallinity......................................224 12.3.4 The Effect of Lattice Strain..................................... 225 12.3.5 The Effect of Temperature and Thermal History����225 12.3.6 The Effect of Atmosphere....................................... 227 12.3.7 The Effect of Electrical Polarization....................... 228 12.4 Influences of Cation Segregation on Electrochemical Activity of SOC Electrodes������������������������������������������������� 229 12.4.1 Influence of Sr Segregation..................................... 230 12.4.1.1 Mechanism 1: Blocking Effects.............. 231 12.4.1.2 Mechanism 2: Inducing Detrimental Side Reactions......................................... 234 12.4.1.3 Mechanism 3: Generating Active Phases......................................................235 12.4.2 A-Site Segregation on Sr-Free Electrode Materials............................................................... 236 12.4.3 Influence of B-Site Segregation.............................. 238 12.5 Surface Engineering Promotes ORR/OER Activity for Perovskite Electrodes����������������������������������������������������������� 239 12.5.1 Surface Decoration with Alkaline Earth Metal Oxides......................................................................240 12.5.2 Surface Decoration of Transition Metal Cations......... 240 12.5.3 Surface Decoration by Secondary PerovskiteBased Phase............................................................. 242 12.5.4 Surface Decoration by Less Activated Phase.......... 245 12.6 Conclusion and Outlook........................................................246 References........................................................................................ 247

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Chapter 13 High-Temperature Electrochemical Process of CO2 Conversion with SOCs 8: Cell and Stack Design, Fabrication, and Scale-Up......... 259 13.1 S  OEC Component/Cell/Stack Structure, Fabrication, and Scale-Up������������������������������������������������������������������������ 259 13.1.1 Component/Cell/Stack Structure............................ 259 13.1.2 Fabrication...............................................................265 13.1.2.1 Particulate Method................................. 265 13.1.2.2 Deposition Method.................................266 13.1.3 Scale-Up..................................................................266 13.2 SOEC Systems...................................................................... 270 13.2.1 System Management............................................... 270 13.2.2 Lab-Scale SOEC Systems....................................... 270 References........................................................................................ 272 Chapter 14 High-Temperature Electrochemical Process of CO2 Conversion with SOCs 9: Degradation Issues.................................................... 275 14.1 Delamination of Oxygen Electrode...................................... 275 14.2 Cr Poisoning of the Oxygen Electrode................................. 278 14.3 SiO2 Poisoning of the Fuel Electrode.................................... 279 14.4 Redox Stability of the Fuel Electrode................................... 281 References........................................................................................ 282 Chapter 15 Economic Analysis of CO2 Conversion to Useful Fuels/ Chemicals........................................................................................ 287 15.1 Methanol............................................................................... 289 15.2 Urea....................................................................................... 291 15.3 Dimethyl Carbonate (DMC)................................................. 291 15.4 Formic Acid.......................................................................... 292 15.5 Syngas (CO+H2)................................................................... 294 15.6 Summary............................................................................... 295 References........................................................................................ 295 Chapter 16 Summary and Possible Research Directions for CO2 Conversion Technologies................................................................. 297 References........................................................................................ 299 Index....................................................................................................................... 301

Preface Continuous increases in the consumption of global fossil fuels has led to a rapid increase in CO2 concentration in our atmosphere. As one of the major contributors to undesired possible climate change and environmental destruction, excessive CO2 emission could disturb the harmony between nature and humans. Developing efficient methods to reduce CO2 and converting it into useful fuels and chemicals are ­obviously one of the solutions for both reducing greenhouse effects and energy s­hortages. Currently, the technologies of CO2 conversion and utilization are not mature and efficient enough in meeting the requirements and overcoming the challenges for practical implementation and commercialization. A book focusing on advanced technologies of CO2 conversion and the associated energy storage is necessary and could have a great impact on the efforts to accelerate the progress of R&D. This book is a comprehensive introduction that focuses on CO2 conversion technologies to produce useful fuels and chemicals. It is a chapter-by-­chapter breakdown of the key topics. The background of CO2 reduction through advanced conversion and utilization technologies is introduced in Chapter 1. Then the fundamentals of CO2 are demonstrated in Chapter 2, including the molecular structure of CO2, the thermodynamics and kinetics of CO2 conversion, and the cause analysis for low activation/conversion rates of CO2. Typical CO2 conversion technologies such as enzymatic, mineralization, photocatalysis, and thermocatalytic are classified and summarized as non-electrochemical methods in Chapters 3 and 4. The electrochemical conversion approaches are divided into low- and high-temperature electrochemical processes; the former is introduced in Chapter 5, and the latter is summarized thoroughly in Chapters 6 through 14. Particularly, as a research topic of our group, the advanced materials and technology of high temperature co-electrolysis of H2O and CO2 to produce sustainable fuels using solid oxide cells (SOCs) are reviewed in detail in these chapters. To be specific, the introduction and fundamentals of CO2/CO2 co-electrolysis using SOCs are introduced in Chapter 6, and the research status is reviewed in Chapter 7. As key topics in SOCs, the materials and their related detection technique are summarized in Chapters 8 and 9. Advanced fabrication methods, advanced structure, and a significant phenomenon are also introduced in Chapters 11 through 13, respectively. As an obstacle to further develop SOCs technique, degradation issues are emphasized in Chapter 14. In addition to analyzing advanced materials and technology used for CO2 conversion, an economic analysis of CO2 conversion into useful fuels and chemicals is given in Chapter 15. The technical and application challenges are analyzed and summarized in Chapter 16, with proposed possible research directions for CO2 conversion technologies to overcome the challenges in future research and applications. This book provides a comprehensive and clear picture of the fundamentals, technologies, and advanced materials for CO2 conversion into useful fuels and chemicals. We hope it will help our readers further understand CO2 reduction through advanced conversion and utilization technologies. We sincerely hope this book will ignite more interest in CO2 issues. xi

Acknowledgments The authors would like to acknowledge the earnest contributions from the Group for High Temperature Electrolysis, the Institute of Nuclear and New Energy Technology (INET), Tsinghua University (Chapter 3: Chenhuan Zhao, Chapter 4: Yifeng Li, Chapter 10: Tong Wu, Chapter 11: Yifeng Li, Chapter 13: Wenqiang Zhang), and the great efforts of Jianxin Zhu, Wangxv Yue and Junwen Cao in editing this book. The authors would also like to acknowledge the support from the National Natural Science Foundation of China (No. 91645126, 21273128, 51425403, and 21677162), the National Key Research and Development Program of China (2017YFB013001), the “Program for Changjiang Scholars and Innovative Research Team in University” (IRT13026), and the “Tsinghua-MIT-Cambridge” Low Carbon Energy University Alliance Seed Fund Program (201LC004).

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Authors Yun Zheng is currently studying for a PhD from the Institute of Nuclear and New Energy Technology (INET) at Tsinghua University, China. He received his BS and MS degrees in chemistry from China Three Gorges University in 2012 and Ocean University of China in 2015, respectively. From 2009 to 2012, he studied in the Engineering Research Center of Eco-environment in Three Gorges Reservoir Region, Ministry of Education, China, for investigations of photocatalysis and photoelectrocatalysis of carbonaceous contaminants using doped semiconductor and organometallic complex materials. His research topics at the Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, China, from 2012 to 2015, were electrodialysis and membrane bioreactor. His current research interests are electrochemical energy storage and conversion, especially for the research of high-temperature electrolysis of CO2/H2O to produce sustainable fuels using solid oxide electrolytic cells (SOECs). Dr. Bo Yu is an associate professor at Institute of Nuclear and New Energy Technology (INET) at Tsinghua University, China. Dr. Yu obtained her BS and MSc in physical chemistry from Northeastern University in 1997 and 2000, respectively. She received her PhD from Tsinghua University in 2004  and joined the Nuclear Science and Engineering Department at Massachusetts Institute of Technology (MIT) as a visiting researcher in 2012. Dr. Yu has been responsible for the research and development of nuclear hydrogen or syngas production through high-temperature electrolysis of CO2/H2O at INET since 2005. Her research interests are electrochemical energy storage and conversion, with some focus on solid oxide cell (SOFC/SOEC) technologies, surface/interface electrochemistry, theoretical and experimental analyses of electrode kinetics, electrocatalysis, and applied electrochemistry. She is the author or co-author of more than 100 peer-reviewed articles, over 30 patents, and several book chapters. Dr. Yu is a Board Member of Nuclear Hydrogen Division of International Associate Hydrogen Energy (IAHE). She is also an Associated Editor of the International Journal of Energy Technology & Policy. xv

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Dr. Jianchen Wang is a professor at the Institute of Nuclear and New Energy Technology (INET) at Tsinghua University, China. He earned his BS degree in physical chemistry and master’s degree in applied chemistry from Tsinghua University in 1987 and 1992, respectively. He has worked at INET since 1987. He obtained a position as an associate professor in 1998 and took a position as a professor in 2004 at INET. He is a deputy director of Committee of nuclear chemistry and radiochemistry, Chinese chemical society. His research interests are in the areas of nuclear chemistry, and separation chemistry in actinides and other nuclear fission elements. He participated in setting up the Chinese partitioning process for high-level liquid waste (HLLW), including the trialkyl phosphine oxides (TRPOs) process to separate actinides, the crown ether process to separate strontium, and the calixcrown process to separate cesium from HLLW. He was awarded the second prize of the State Technological Invention of China for his contribution to researching TRPO process. He is the author or co-author of more than 60 peer-reviewed articles and over 30 patents in these areas. In recent years, his research area also includes electrochemistry, including high-temperature co-­ electrolysis (HTCE) of H2O and CO2 by using solid oxide electrolytic cells (SOECs) and the disintegration of graphite matrix from spent fuel of high-temperature gascooled reactors (HTGRs) by electrochemical technology. Dr. Jiujun Zhang is a professor at Shanghai University and Principal Research Officer (Emeritus) at National Research Council of Canada  (NRC). Dr.  Zhang received his BS and MSc in electrochemistry from Peking University in 1982 and 1985, respectively, and his PhD in electrochemistry from Wuhan University in 1988. After completing his PhD, he took a position as an associate professor at the Huazhong Normal University for two years. Starting in 1990, he carried out three terms of postdoctoral research at the California Institute of Technology, York University, and the University of British Columbia. Dr. Zhang has over 30 years of R&D experience in theoretical and applied electrochemistry, including over 18 years of fuel cell R&D (including six years at Ballard Power Systems and 12 years at NRC-IFCI (before 2011; NRC-EME after 2011), and three years of electrochemical sensor experience. Dr. Zhang holds several adjunct professorships, including one at the University of Waterloo, one at the University of British Columbia, and one at Peking University. Dr. Zhang has co-authored more than 400 publications, including 230 refereed journal papers with approximately

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22,000 citations, 18 edited or co-authored books, 41 book chapters, as well as 110 conference and invited oral presentations. He also holds over 10 US/EU/WO/JP/CA patents and 11 US patent publications, and he has produced more than 90 industrial technical reports. Dr. Zhang serves as the editor or as an editorial board member for several international journals as well as editor for a book series (Electrochemical Energy Storage and Conversion, CRC Press). Dr. Zhang is an active member of the Electrochemical Society (ECS), the American Chemical Society (ACS), and the Canadian Institute of Chemistry (CIC); a Fellow Member of the International Society of Electrochemistry (ISE); as well as a board committee member of the International Academy of Electrochemical Energy Science (IAOEES).

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Introduction to CO2 Reduction through Advanced Conversion and Utilization Technologies

1.1  GLOBE ENERGY STATUS, CHALLENGES, AND PERSPECTIVES Energy is one of the most important strategic resources for social development and national economy. According to the data from the International Energy Agency (IEA), as shown in Figure 1.1, global energy needs in the new policies scenario will still increase by 30% between today and 2040, although it will rise more slowly than in the past. This increased energy need is basically the equivalent of adding another China and India to today’s global demand.1 By comparison, the largest portion of this energy demand growth (about 30%) comes from India, and its global energy consumption will rise to 11% by 2040. Southeast Asia is also an important contributor in global energy demand, and its growth rate will be twice of China. In short, about two-thirds of global energy growth results from the developing countries in Asia, and some other countries and regions including the Middle East, Africa and Latin America.1 With respect to the specific energy resources, in the last nearly two decades, global consumption of fossil fuels such as coal, oil, and gas have still increased significantly (a typical example of China is shown in Figure 1.2),1 thus increasing the levels of CO2 in our atmosphere greatly and leading to undesired climate change and environmental destruction.2 Meanwhile, the limited reserves of coal and gas on the earth will gradually dry up with over-exploitation. Accordingly, as proposed by the IEA, energy consumption should be changed dramatically in the future with reference to new policies scenario; specifically, decreased use of coal and oil, rapid increase in the use of renewables and enhanced energy efficiency are necessary to deal with above issues. The development of advanced energy conversion and storage technologies should therefore be explored in conjunction with the exploration of clean, renewable alternative energy sources, especially solar radiation, wind, and so on.3–8

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Carbon Dioxide Reduction

FIGURE 1.1  Growing global energy demand from 2016 to 2040. (From World Energy Outlook 2017, International Energy Agency, Paris, France, 2018.)

FIGURE 1.2  Primary energy demand by fuel in China from 2000 to 2016. (From World Energy Outlook 2017, International Energy Agency, Paris, France, 2018.)

1.2 CO2 EMISSION AND REDUCING Continuously increasing global consumption of fossil fuels has led to the rapid growth of CO2 concentrations in our atmosphere.9,10 As one of the major contributors to undesired climate change and environmental destruction, excessive CO2 emissions

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Introduction to CO2 Reduction through Advanced Technologies

have greatly affected our world despite it being a necessary material for life and many industrial processes.10–12 Despite their recent flattening, global energy-related CO2 emissions will still increase slightly through 2040 in the new policies scenario. This outcome is far from enough to avoid severe impacts of climate change; thus, it is critical to develop efficient methods for reducing CO2 emissions and exploring green and sustainable energy resources.13,14 For this purpose, several treatment systems to reduce CO2, including more efficient electric energy production, better energy utilization effciency, fuel shift (from coal to gas), carbon capture and storage, and conversion have been proposed by researchers (more details are shown in Table  1.1).14 Based on important factors such as cost, energy resource distribution, and implementation time, the reduction and conversion of CO2 into useful fuels/chemicals for utilization is an attractive solution that reduces greenhouse effects and provides effective energy sources.11,15 TABLE 1.1 Strategies for Reducing CO2 Emission Strategies Higher efficiency in electric energy production

Utilization of energy with better efficiency

Fuel shift

Carbon capture and storage (CCS)

CO2 conversion and utilization

Features

Limitations

Use of innovative technologies usually. Efficiency improvements from  oil > gas (497)b Large potential in CO2 storage Storage in natural fieldsc Not been accepted by many countries Recycles carbon Reduces the extraction of fossil-C Avoids emission of CO2

High costs and long implementation times

Source: Aresta, M. et al., Chem. Rev., 114, 1709–1742, 2014. a IGCC: integrated gasification combined cycle. b Emissions of CO per kWh of electric energy generated, g/kWh. 2 c For example, depleted oil and gas fields, aquifers, and coal beds.

Difficulties for unified plan and control

Distribution of resources Security and economic (costly, uncertainty, intensive energy requirements)

4

Carbon Dioxide Reduction

1.3 MAIN APPROACHES OF CO2 CONVERSION AND UTILIZATION Generally, the conversion of CO2 can be divided into two reaction categories (Figure 1.3). One uses less energy supply to convert CO2 into high-carbon organic chemicals with its carbon in an oxidation state of +4 or +3; such conversion reactions also tend to happen at temperature below 273 K. The other uses greater energy to reduce CO2 into low-carbon chemicals/fuels with its carbon in the reductive states of +2 or lower. Typical products in the two categories are shown in Figure 1.3. In terms of global market demands, fuels face significantly higher demand than do chemicals (12–14 times)14,16 and the manufacture of fuels convert significantly greater volumes of CO2 (Gt/y) than that of chemicals (>300 Mt/y). Regarding the specific approaches for CO2 conversion and utilization (see  Figure 1.4), there are three main approaches: chemical/catalytic conversion (chemical process), enzymatic conversion (biological/biochemical process), and technological utilization (physical process). Here, technological utilization is not closely related to CO2 conversion because of its physical nature, including compressing, recycling, phase transition, and so on. However, it is important for the practical usage of CO2 which includes cereal preservation (bactericide), additives to beverages, food packaging/conversion, dry cleaning, extraction, mechanical industries, fire extinguishers, air-conditioning as well as water treatment.13,14 CO2 enzymatic conversions (such as photosynthesis)10,17–20 and mineralization21–27 are the most common methods for the conversion/fixation of CO2. CO2 mineralization, from CO2 to inorganic or organic hydro-carbonate (HCO3−)/carbonate(CO32−) (ΔG  0), showing that the conversion reactions are non-spontaneous. Additionally, with respect to the standard enthalpy changes (ΔHθ > 0) of various products listed in Table 2.1, the ΔHθ values of all these conversion reactions are also positive, demonstrating that these CO2 conversion processes are endothermic under a standard state. Thermodynamic parameters (Gibbs free energy change [ΔG], enthalpy change [ΔH], and entropy change [ΔS]) are a function of temperature. ΔG of CO2 conversion reactions at 298.15 K or even at other temperatures can be calculated with reference to some thermodynamic equations (Equations 2.1 through 2.6) and parameters of CO2 (Table 2.2) and other reactants or products.9 Even with exothermic reactions (ΔH  0) due to the effects of entropy (S) and temperature (T) in accordance with Equation (2.1). Therefore, negative thermodynamics can make the conversion unfeasible even at higher temperature. ΔG = ΔH − TΔS (2.1)



∆H (298.15 K) =



∑ ν ∆ H (298.15 K) (2.2) B

f

B

B

∆S (298.15 K) =



∑ ν S (298.15 K) (2.3) B B

B



∆H (T) = ∆H (298.15 K) +



∆S (T) = ∆S (298.15 K) +

∫

T

∫

T

298.15K

298.15K

∆C p =



∆C pdT

(2.4)

∆C pdT

(2.5)

∑ ν C (B) (2.6) B

p

B

where in Equations (2.1) through (2.6), ΔH is the enthalpy change (kJ·mol−1); Δf HB is the enthalpy of formation for B (kJ·mol−1); S is the entropy (kJ·mol−1 K−1); ∆S is the entropy change (kJ·mol−1 K−1); T is the temperature (K); ΔG is the Gibbs free energy change (kJ·mol−1); Cp is the heat capacity (J·mol−1K−1); and ∆Cp is the heat capacity change (J·mol−1 K−1).

TABLE 2.2 Thermodynamic Parameters of CO2 at 298.15 K and 101.325 kPa (Here the Definitions of Other Parameter Symbols Are Presented Above in the Text)

CO2(g)

ΔfGθ (kJ∙mol−1)

ΔfHθ (kJ∙mol−1)

Sθ (kJ∙mol−1∙K1)

Heat Capacity (Cp) (J∙mol−1∙K−1)

−394.4

−393.5

0.214

44.141 + 0.00904T − 853500/T2

Source: Ihsan, B., ed., Thermochemical Data of Pure Substances, WILEY-VCH Verlag GmbH, New York, 1993.

13

Fundamentals of CO2 Structure, Thermodynamics, and Kinetics

For an equilibrium reaction, the ΔGθ can be closely related to the standard equilibrium constant K θf (Equation 2.7), where R is the molar gas constant (J·mol−1·K−1). In addition, the relationship between temperatures and ΔGθ is needed to obtain the equilibrium constant at a reaction temperature. This relationship can be expressed with reference to Van’t Hoff equation (Equation 2.8), where p represents the constant pressure. For CO2 conversion, the heat of the reaction and the equilibrium constant can be calculated as shown in Table 2.3; it is seen that increasing pressures, for example, from 1 to 6 MPa, can increase the equilibrium conversion process.10 However, increasing temperature in a certain range may slow down some equilibrium conversions (e.g., production of CH4, C2H4, CH3OH, C2H5OH), although increasing temperature can speed up other conversion processes such as the production of HCHO and HCOOH.10 Therefore, higher temperatures are not always conducive to CO2 conversion.

∆G θ = −RT lnK θf (2.7)



 ∂lnK θf  ∆H θ (2.8)   = 2  ∂T P RT

TABLE 2.3 Heat and Equilibrium Constants of Several CO2 Conversion Reactions at Ideal State Reaction CO2 + 4H2 = CH4 + 2H2O

2CO2 + 6H2 = C2H4 + 4H2O

CO2 + 3H2 = CH3OH + H2O

2CO2 + 6H2 = C2H5OH + 3H2O

CO2 + 2H2 = HCHO + H2O

CO2 + H2 = HCOOH

Tem. (°C)

ΔHθ, (kJ/mol)

25 100 200 25 100 200 25 100 200 25 100 200 25 100 200 25 100 200

−0.16486E+3 −0.16819E+3 −0.17211E+3 −0.12791E+3 −0.13230E+3 −0.13720E+3 −0.49449E+2 −0.52464E+2 −0.55839E+2 −0.17314E+3 −0.17828E+3 −0.18383E+3 0.35739E+2 0.41270E+2 0.51494E+2 0.14881E+2 0.13797E+2 0.12982E+2

Source: Gao, F. et al., J. Nat. Gas. Chem., 10, 24–33, 2001.

K θf 0.82755E+20 0.11260E+15 0.10359E+10 0.12223E+11 0.32014E+6 0.32913E+2 0.26804 0.43142E−2 0.10792E−3 0.28230E+12 0.18262E+6 0.79786 0.16345E−9 0.36155E−8 0.81597E−7 0.25001E−7 0.48226E−6 0.68332E−6

14

Carbon Dioxide Reduction

2.3  KINETICS OF CO2 CONVERSION In CO2 conversion reactions, the C atom in the molecule is normally first attacked. In an addition reaction, the nucleophile first attacks the C atom with a partially positive charge (Figure 2.5). The nucleophile can be a neutral species with a lone pair of electrons (e.g., an amine) and can possess a C-metal σ bond (e.g., a Grignard reagent) or an electron-rich π bond (e.g., a phenolate).6 In such situations, the chemical reactivity of CO2 depends on the polarization of O and C bonds, and the kinetics is dominated by both CO2 and nucleophiles. In terms of the chemistry of CO2, the other key feature is its coordination to metals. The electron distribution and molecular geometry within the CO2 molecule can be changed significantly via the coordination of CO2 to a metal. Generally, the electrons in the bonding orbitals of CO2 can act as an electron donor (referred to as μa–ηb, where “a” donates receptor number, and “b” donates donor number), weakening the bond between C and O, and leading to increased chemical reactivity. Several CO2-metal complex geometries are shown in Figure 2.6.

FIGURE 2.5  Addition reaction of carbon dioxide with nucleophiles. (From North, M., Chapter 1: What is CO2? Thermodynamics basic reactions and physical chemistry, in Styring,  P. et al. (Eds.), Carbon Dioxide Utilisation: Closing the Carbon Cycle, Elsevier, Oxford, UK, 2015.)

FIGURE 2.6  Metal complex geometries of CO2. η1C is for the coordination of a metal to one C atom; η1O is for the coordination of a metal to one of the O atoms; the n in μ n is for the number of metals; and the m in ƞm is for the number of M-C/O bands. (Reprinted from North, M., Chapter 1: What is CO2? Thermodynamics basic reactions and physical chemistry, in Styring, P. et al. (Eds.), Carbon Dioxide Utilisation: Closing the Carbon Cycle, Elsevier, Oxford, UK, Copyright 2015, with permission from Elsevier.)

Fundamentals of CO2 Structure, Thermodynamics, and Kinetics

15

From a thermodynamic standpoint, as mentioned above, a reaction is spontaneous when its Gibbs free energy change is favorable (ΔG > 0). Nevertheless, some reactions may still be non-spontaneous due to high activation energies. Consequently, these CO2 conversion reactions require a suitable catalyst. Catalysts can lower activation energies and allow or even accelerate the reaction at suitable temperatures. For example, in the production of ethylene carbonate from ethylene oxide and CO2, even with remarkably favorable ΔG (−56 kJ/mol) and ΔH (−144 kJ/mol), a suitable catalyst is required for the reaction to occur. This can be interpreted with Figure 2.7 where four types of CO2 conversion reactions (A−D) are defined. The reaction pathway energy diagrams are divided into two groups, also shown in Figure 2.7: (a) the processes of reactions A and B, both of which possess a negative Gibbs free energy change (ΔG  0). In group (a) mentioned above, the activation energy (ΔG*) of reaction B is much higher than that of A, thus, reaction A is expected to occur without the need of a catalyst whereas a catalyst is necessary for reaction B due to its significant activation energy. The synthesis of sodium salicylate from CO2 and sodium phenolate is a good example of reaction A and the production of ethylene carbonate from CO2, and ethylene oxide is a good example of reaction B. One thing to note here is that simply promoting the reaction temperature may not always be effective in overcoming the activation barrier as the ΔG will be positive if the ΔS of the reaction is negative. In group (b), with regard to reaction C in Figure 2.7, the ΔG* is slightly higher than ΔrG (the Gibbs free energy change of CO2 conversion reactions), thus catalysts are not needed, but the removal of the formed products is challenging. Therefore, the reaction equilibrium will shift positively or even not occur. Compared with

FIGURE 2.7  (a, b) Reaction pathway energy diagrams for reactions of carbon dioxide. Here ΔrG is the Gibbs free energy change of CO2 conversion reactions. (Reprinted from North, M., Chapter 1: What is CO2? Thermodynamics basic reactions and physical chemistry, in Styring, P. et al. (Eds.), Carbon Dioxide Utilisation: Closing the Carbon Cycle, Elsevier, Oxford, UK, Copyright 2015, with permission from Elsevier.)

16

Carbon Dioxide Reduction

reaction C, the ΔG* of reaction D is much higher than its ΔrG. This is the most challenging situation and unfortunately it is common in CO2 conversions. Consequently, an effective catalyst for reducing ΔG* is necessary, one that can facilitate the reaction at a lower and more suitable temperature, because lower reaction temperatures can contribute to a decrease in ΔrG and an increase in equilibrium constant for the reaction. It is recognized that poor catalytic activity and/or insufficient stability of catalysts are the largest challenges in CO2 conversions (especially in CO2 electroreduction).11 Thus, CO2 conversion is also difficult from a kinetics standpoint.12

2.4 SUMMARY CO2 is thermodynamically and kinetically stable, making its conversions to other chemicals/fuels difficult. However, CO2 can be attacked by nucleophiles and ­electron-donating reagents ascribe to the electron deficiency of carbonyl carbons.13 Therefore, the conversion of CO2 is achievable in practice despite technological barriers.14 Typical approaches, especially for the production of fuels with high energy exchange, are detailed in following chapters.

REFERENCES 1. Armenise, I., Kustova, E. V. State-to-state models for CO2 molecules: From the theory  to an application to hypersonic boundary layers. Chemical Physics 415, ­ 269– 281 (2013). 2. Rothman, L. S., Hawkins, R. L., Wattson, R. B. Energy levels, intensities, and l­ inewidths of atmospheric carbon dioxide bands. Journal of Quantitative Spectroscopy & Radiative Transfer 48, 573–566 (1992). 3. Stanbury, M. et al. Mn-carbonyl molecular catalysts containing a redox-active ­phenanthroline-5, 6-dione for selective electro- and photoreduction of CO2 to CO or HCOOH. Electrochimica Acta 240, 288–299 (2017). 4. Ishida, S., Iwamoto, T., Kabuto, C. A stable silicon-based allene analogue with a ­formally sp-hybridized silicon atom. Nature 421, 725–727 (2003). 5. Aresta, M., Dibenedetto, A., Quaranta, E. State of the art and perspectives in ca talytic processes for CO2 conversion into chemicals and fuels: The distinctive contribution of chemical catalysis and biotechnology. Journal of Catalysis 343, 2–45 (2016). 6. North, M. Chapter 1: What is CO2? Thermodynamics basic reactions and p­ hysical chemistry. In Styring, P., Quadrelli, A., Armstrong, K. (Eds.). Carbon Dioxide ­ Utilisation: Closing the Carbon Cycle (Elsevier, Oxford, UK, 2015). 7. Aresta, M., Dibenedetto, A., Angelini, A. Catalysis for the valorization of exhaust ­carbon: From CO2 to chemicals, materials, and fuels. Technological use of CO2. Chemical Reviews 114, 1709–1742 (2014). 8. Yang, M., Xu, Y. Photocatalytic conversion of CO2 over graphene-based composites: Current status and future perspective. Nanoscale Horizons 1, 185–2 (2016). 9. Ihsan, B. (ed.) Thermochemical Data of Pure Substances (WILEY-VCH Verlag GmbH, New York, 1993). 10. Cao, F. et al. Thermodynamic analysis of CO2 direct hydrogenation reaction. Journal of Natural Gas Chemistry 10, 24–23 (2001). 11. Qiao, J., Liu, Y., Hong, F., Zhang, J. A review of catalysts for the electroreduction of carbon dioxide to produce low-carbon fuels. Chemical Society Reviews 43, 631–675 (2014).

Fundamentals of CO2 Structure, Thermodynamics, and Kinetics

17

12. Gao, S. et al. Partially oxidized atomic cobalt layers for carbon dioxide electroreduction to liquid fuel. Nature 529, 68–71 (2016). 13. Sakakura, T., Choi, J., Yasuda, H. Transformation of carbon dioxide. Chemical Reviews 107, 2365–2387 (2007). 14. Aresta, M., Dibenedetto, A., Angelini, A. The use of solar energy can enhance the conversion of carbon dioxide into energy-rich products: Stepping towards artificial photosynthesis. Philosophical Transaction A Mathematical Physical and Engineering Sciences 371, 20120111 (2013).

3

Enzymatic and Mineralized Conversion Process of CO2 Conversion

3.1  ENZYMATIC CONVERSION OF CO2 As one of the most widespread processes in nature, enzymatic conversion of CO2 is absolutely essential for life and biological evolution. Enzymatic conversion of CO2 is advantageous for its high efficiency and non-polluting nature thanks to the specificity and selectivity of the biological reaction.1–3 The Calvin cycle, the 3-hydroxypropionate cycle, and the reductive citric acid cycle are the most common approaches of the enzymatic conversion of CO2 in cells. As the most important biosynthetic cycle in nature, the Calvin cycle is exists in plants, cyanobacteria, algae, and so on.4 The process of converting hydro-carbon chemicals/fuels (CnHm) to CO2 is exothermal and easily facilitated due to a negative Gibbs free-energy (ΔG  0). Figure 3.1a shows the principle of photosynthesis in nature. Typical photosynthesis consists of a light reaction from H2O to O2 by daylight and a dark reaction (Calvin cycle) from CO2 to organic substance like glucose.5 Significantly, the committed step for enzymatic conversion of CO2 is the Calvin cycle. The Calvin cycle includes three stages, as shown in Figure 3.1b. First, the first key enzyme 1,5-bisphosphate ribulose bisphosphate carboxylaset accelerates the reaction from CO2 and 1,5-bisphosphate ribulose to 3-­ phosphoglycerate. Then, 1,3-diphosphoglycerate is generated from 3-phosphoglycerate and a Pi, further producing 3-phosphate glyceraldehyde by the second key enzyme phosphoglyceral-dehyde dehydrogenase. Finally, 5-phosphate ribulose is produced from 5/6 of the generated 3-phosphate glyceraldehyde and further transformed into 1,5-bisphosphate ribulose, which forms the reactant with CO2 in the next cycle. At the same time, the extra 3-phosphate glyceraldehyde transforms to organic substances such as sugar, fatty acids, and amino acids as shown in Figure 3.1b. Meanwhile, the nicotinamide adenine dinucleotide phosphate (NADPH) acts as a proton carrier and a hydrogen source, and the transformation of adenosine triphosphate (ATP) into adenosine diphosphate (ADP) provides energy for enzymatic conversion of CO2. Except for CO2 conversion in cells, there are different enzymatic conversion approaches with other enzymes for producing chemicals/fuels, as listed in Table 3.1.1 According to the types of catalytic enzyme, the conversion approaches are sorted into two large categories, namely, single enzyme and multienzyme systems. In regard to CO2 conversion with single enzyme catalytic, Reda et al. have developed a typical approach for formate production facilitated by an electro-active enzyme 19

20

Carbon Dioxide Reduction

FIGURE 3.1  (a) Process of photosynthesis. (Reprinted from Appl. Catal. B Environ., Lee, W. et al., A novel twin reactor for CO2 photoreduction to mimic artificial photosynthesis, 132–133, 445–451, Copyright 2013, with permission from Elsevier.) (b) The Calvin cycle. (Shi, J. et al., Chem. Soc. Rev., 44, 5981–6000, 2015, Reproduced by permission of The Royal Society of Chemistry.)

21

Enzymatic and Mineralized Conversion Process of CO2 Conversion

TABLE 3.1 Some Products from CO2 Conversion with Different Enzymes In Vitro Products Formate (HCOO−) Formate (HCOO−) Carbon monodioxide (CO) Methane (CH4) Bicarbonate (or minerals) (HCO3−) Biodegradable chemicals (e.g., CH3COCOOH) Methanol (CH3OH)

Specific Enzymea

References

Formate dehydrogenase (FateDH) Carbon dioxide reductase Carbon monodioxide dehydrogenase (CODH) Remodeled nitrogenase Carbonic anhydrase (CA)

7–9

Decarboxylases (e.g., pyruvate decarboxylase)

1,24

Multiple dehydrogenases (e.g., FateDH + FaldDH + ADH)

25,26

10,11 12–16 17,18 19–23

Source: Shi, J. et al., Chem. Soc. Rev., 44, 5981–6000, 2015. a F DH, formaldehyde dehydrogenase; ADH, alcohol dehydrogenase. ald

(tungsten-containing formate dehydrogenase enzyme), as shown in Figure  3.2a.27 The conversion reaction is reversible, where the process occurs on the formate dehydrogenase enzyme when two electrons transfer from the electrode to the tungsten active site. Yadav et al.9 have proposed another approach with four stages for CO2 conversion to formic acid in an artificial photosynthesis system facilitated by photocatalysts and enzymes simultaneously, as shown in Figure 3.2b. First, the photon absorption occurs as an exchange between located orbitals around a chromophore. Second, a rhodium (Rh) complex is reduced after receiving an electron. Third, the reduced rhodium complex helps to extract a proton, with some electrons and a hydride transferred to nicotinamide adenine dinucleotide (NAD+) for reduced nicotinamide

FIGURE 3.2  Schematics of (a) a typical approach for formate production facilitated by an electro-active enzyme (Reprinted with permission from Reda, T. et al., 2008. Reversible interconversion of carbon dioxide and formate by an electroactive enzyme. Proc. Natl. Acad. Sci. USA, 105, 10654–10658. Copyright 2008 National Academy of Sciences, U.S.A.) and (b) the artificial photosynthesis for HCOOH generation from CO2. (Reprinted with permission from Yadav, R.K. et al., J. Am. Chem. Soc., 134, 11455–11461, 2012 American Chemical Society.)

22

Carbon Dioxide Reduction

FIGURE 3.3  The schematic of overall process of CO2 conversion to CH3OH with enzymes TateDH-formate dehydrogenase, TaldDH-formaldehyde dehydrogenase and ADH-alcohol dehydrogenase. (Reprinted from J CO2 Util., Aresta, M. et al., 3–4, The changing paradigm in CO2 utilization, 65–73, Copyright 2013, with permission from Elsevier.)

adenine dinucleotide (NADH) generation. Finally, the generated NADH is used up for the CO2 conversion to HCOOH with formate dehydrogenase. Formate or HCOOH are the common products in single enzyme systems, while other products are CO, CH4, HCO3−, and other chemicals with various enzymes in vitro, as listed in Table 3.1. The typical instance in the multienzyme system is the conversion from CO2 to CH3OH. This conversion process includes three steps with corresponding enzymes: the first step is the transformation from CO2 into HCOOH, which is facilitated by formatdehydrogenase (TateDH enzymes). Second, formaldehydedehydro (TaldDH enzymes) further change HCOOH into HCHO, followed by the transformation of HCHO into CH3OH facilitated by alcohol dehydrogenase (ADH). As shown in Figure 3.3, NADH supplies electrons for the conversion reaction, and the overall conversion process is accompanied by three 2e− transfers. In this section, we have submitted a series of conversion processes for enzymatic conversions of CO2. Although these processes are environmentally friendly and highly efficient methods to transform CO2 into chemicals/fuels, it should be noted that more research about enzyme conversion process is needed to further promote the conversion effciency and facilitate the reaction kinetics, especially for industrialization.

3.2  MINERALIZATION PROCESS OF CO2 CONVERSION The mineralization of CO2 is valued for the large-scale CO2 storage and conversion of CO2 to chemicals.28 The complex conversion process consists of carbonation of silicide and formation of stable carbonate minerals.29–31 The CO2 mineralization is inspired by the natural reaction of CO2 absorption to silicide. It has been reported by Seifritz32 that CO2 and CaSiO3 can be converted together into Ca2+, HCO3− and SiO2 with the participation of water. In nature, CO2 can be gathered by silicate minerals such as serpentine (Mg3Si2O5(OH)4(s)), olivine (forsterite, Mg2SiO4(s)), wollastonite (CaSiO3(s)), talcum, pyroxenes and amphiboles and then transformed to solid ­products that are applied as material of construction, fire retardants, and so on.33–36 The process of chemical transformation is37,38:

Enzymatic and Mineralized Conversion Process of CO2 Conversion



23

(Mg, Ca)xSiyOx+2yH2z + xCO2 → x (Mg, Ca)CO3 + ySiO2 + zH2O (3.1)

Mg3Si2O5(OH)4 (s) + 3CO2 (g) → 3MgCO3 (s) + 2SiO2 (s) + 2H2O (l) (3.2) Mg2SiO4 (s) + 2CO2 (g) → 2MgCO3 (s) + SiO2 (s)

(3.3)

CaSiO3 (s) + CO2 (g) → CaCO3 (s) + SiO2 (s)

(3.4)

According to the ΔfG θ of typical products shown in Table 3.2, the overall conversion reactions for the carbonation of silicate minerals process in nature are exothermic and occur spontaneously by thermodynamics (ΔG50% Up to 85% LHV

3.7 kWh/Nm3 40 Nm3/h 10 bar (g) 99.999% Atmospheric dew point temperature: −60°C On request Saturated steam: Mass flow: 40 kg/h Pressure: 2–3 bar (g)

Emissions Installation Electrical interface Noise Ambient air temperature Communication

Power Generation

9 100

−2

60

10 207

80

>28 >332

Source: Aresta, M. et al., J. Catal., 343, 2–45, 2016.

n

( mp ⋅Wp ) − Relative added value =

n

∑ (m

E, i

⋅WE,i )

i

∑ (m

E, i

(15.1)

⋅ WE,i )

i

With respect to the economic analysis of CO2 conversions into useful fuels/chemicals in a specific production process or a chemical plant, the fixed capital costs, variable/ fixed costs of production, product prices, and so on, of each product depends strongly on the product category, plant capacity, production processes, and even the difference between various countries and regions. Hence, it is difficult to compare systematically the costs of CO2 conversion to different useful chemicals/fuels. Therefore, economic analysis for various typical chemicals/fuels will be reviewed in various cases in this section. Note that all economic analysis in the literature is based on normal electricity costs. If redundant electricity from clean energy and/or nuclear sources is used, the results of the process economics can be different, allowing the process to be more profitable. In addition, the environmental benefits from CO2  reduction is normally not considered in the following analysis. Aside from these two points, the environment benefits from CO2 reduction is far more important than the economic benefits.

Economic Analysis of CO2 Conversion to Useful Fuels/Chemicals

289

FIGURE 15.1  Relative added value of various chemicals/fuels for different CO2 price. (Otto, A. et al., Energ. Environ. Sci., 8, 3283–3297, 2015. Reproduced by permission of The Royal Society of Chemistry.)

15.1 METHANOL Due to its versatility in the synthesis of several important chemicals such as acetic acid, chloromethane, alkyl halides, formaldehyde, and even higher hydrocarbons, methanol (CH 3OH) is a common feedstock and a building block in the chemical industry.1,3–5 In 2014, around 60% of the produced methanol was used for the production of these chemicals, with the remaining 40% used for the production of fuels such as biodiesel, di-methyl-ether (DME), marine fuels, and so on.6 Normally, the ­production of methanol is performed via a hydrogenation (CO2+H 2) and bi-­reforming (CO2+natural gas) process. More recently, Kourkoumpas et al.6 performed a techno-economic investigation into the implementation of “power to methanol (PtM)” using CO2 from lignite power plants. Their concept consists of electricity generation, CO2 capture and

290

Carbon Dioxide Reduction

FIGURE 15.2  (a) Diagram of power to methanol (PtM), (b) the cost breakdown of two cases (the power plant owner case, and (c) and the private investor case. (Reprinted from Int. J. Hydrog. Energy, 41, Kourkoumpas, D.S. et al., Implementation of the Power to Methanol concept by using CO2 from lignite power plants: Techno-economic investigation, 16674–16687, Copyright 2016, with permission from Elsevier.)

separation (CCS), H 2 production, as well as key stages of methanol production and application, as shown in Figure 15.2a. Two distinct case studies, a power plant owner case and a private investor case, were selected as cost breakdowns, shown in Figure 15.2b and c. In this figure, the methanol cost is estimated, and the results show that the cost for the power plant owner was 421 € ton−1 which was approximately 40% lower than that of the other case (580 € ton−1) due to lower electricity costs and larger operating capacities of H 2 and methanol plants in the former. In addition, other economic analyses for conversion into methanol have been studied7,8 and it is believed that methanol costs can be further reduced through the development of related technologies.

291

Economic Analysis of CO2 Conversion to Useful Fuels/Chemicals

15.2 UREA Urea (NH2CONH2) is usually commercialized as a solid, typically as granules or prills. There are four steps in the production of urea including the reaction of CO2 and ammonia, low-pressure recirculation and purification, as well as granulation.9 Bose et al.10 proposed a coal-based poly-generation by first capturing CO2 and then using the captured CO2 to produce urea, a common fertilizer. The economic analysis of this proposed process is presented in Table 15.2 The utilization and recycling of waste is essential for sustainability, and utilizing waste can increase economic feasibility.

15.3  DIMETHYL CARBONATE (DMC) Based on CO2  conversion, dimethyl carbonate ((CH3O)2CO) can be synthesized through four proposed processes: (1) CO2 and methanol directly, (2) urea, (3) propylene carbonate, and (4) ethylene carbonate. As a typical CO2 conversion for dimethyl carbonate production, the techno-economic evaluation of this process using novel catalytic membrane reactors was studied,11 especially for investment costs and operating costs, as listed in Tables 15.3 and 15.4, respectively (the production DMC is TABLE 15.2 Data for Economic Analysis of the Proposed Process of Urea Production Parameters

Value 45 $/MT 80 $/MWh 14.1 $/ton 3.66 $/GJ 570.5 $/MT

Cost of urea plant Cost of electricity Average cost of CO2 transport and sequestration Cost of utility heat Revenue earned through urea Source:

Bose, A. et al., Clean Technol. Environ. Policy, 17, 1271–1280, 2015.

TABLE 15.3 Overview of the Investment Costs for a typical CO2 conversion for dimethyl carbonate production process Equipment Type Membrane reactor Flash vessels Distillation columns Compressors Pumps Heat exchangers Total investment cost

Costs [M$]

Costs [M$]

Total Costs [M$]

– 0.2 1.3 1.1 0.1 – 2.7

1.7 0.3 2.0 1.5 0.1 2.0 7.6

10.1 1.8 11.7 9.2 0.8 11.9 45.5

Source: Kuenen, H.J. et al., Comput. Chem. Eng., 86, 136–147, 2016.

292

Carbon Dioxide Reduction

TABLE 15.4 Overview of the Operating Costs for a typical CO2 conversion for dimethyl carbonate production process Parameters Raw materials Utilities Electricity (0.06$/kWh) Chilled water (4$/GJ) Cooling water (0.05$/m3) Hot water −95°C (0.05$/m3) Steam 2 bar (5$/ton) Steam 5 bar (7$/ton) Steam 20 bar (12$/ton) Operations (labor related) Maintenance Operation overhead Property taxes Depreciation Depreciation (8%) Membrane life time (3 years) Cost of manufacture General expenses Total production cost Sales (DMC) Revenue

Costs [M$y–1]

Costs [M$y–1] 6.63 4.18

0.83 0.77 0.40 0.004 0.60 0.54 1.05 1.32 3.66 0.74 0.91 4.07 3.50 0.56 21.51 2.31 23.82 20.00 −3.82

Source: Kuenen, H.J. et al., Comput. Chem. Eng., 86, 136–147, 2016.

20 kton y−1). Here, the DMC price is 1000$/ton, and the methanol price is 445$/ ton, with the CO2 cost being zero. It can be concluded that, under the performed conditions, the production process is unprofitable due to the high costs of depreciation, maintenance, and utilities.

15.4  FORMIC ACID Formic acid (HCOOH) is a chemical that is widely used in textiles, food chemicals, and pharmaceuticals. It also has potential to be a hydrogen carrier and fuel that can be directly used for fuel cells. Formic acid is a high-value product because it has a concentrated, mature, and small market with low risk of substitution.12 The process of CO2  utilization for formic acid production is shown in Figure 15.3a, with the installed and operating costs of this plant also being depicted in Figure 15.3b and c. Forty-three percent of the total installed cost is for electrolysis, and the remaining costs are for the compression and separation processes. Utilities and consumables such as steam and electricity are the main contributors to operating costs.

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FIGURE 15.3  (a) Process of carbon dioxide utilization for formic acid production and the breakdown of (b) operating costs and (c) installed costs. (Reprinted from Int. J. Hydrog. Energy, 41, Pérez-Fortes, M. et al., Formic acid synthesis using CO2 as raw material: Technoeconomic and environmental evaluation and market potential, 16444–16462, Copyright 2016, with permission from Elsevier.)

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The  revenue of formic acid and other by-products are approximately 50% of the production costs. Therefore, more research, including R&D for electrolyzers, coupling with renewable energies, as well as developments of other related technologies to lower the cost for CO2 conversion to produce formic acid, is needed.

15.5  SYNGAS (CO+H2) Compared to low-temperature electrochemical conversion of CO2, the selectivity of products such as CO (electrolysis) and CO/H2 (CO2/H2O co-electrolysis) at high temperatures using solid oxide cell (SOC) is preferable. In the synthetic natural gas (SNG) production of integrated high-temperature electrolysis (steam electrolysis or H2O/CO2 co-electrolysis using SOC) and methanation of CO2, the effects of the following essential parameters were further investigated: CO2 feedstock costs, cell degradation rates, and electrolysis stack costs. Figure 15.4 shows the share and specific costs of each category. It is evident that electricity is the most relevant cost.

(a)

(b)

(c)

(d)

FIGURE 15.4  Specific share and cost for each category: (a) SOEC, (b) plant, (c) cost of production (COP) behavior of varied electricity feedstock prices, (d) SNG COP versus electricity costs for the co-electrolysis plant operating and limit voltage under target case assumptions. SE: steam electrolysis; CE: co-electrolysis; lim: limit; tn: thermoneutral; FT&P: foundations, transport, and placement; HEN: heat exchanger network; ZOGB: zinc oxide guard bed; O&M includes carbon dioxide cost, spare capacity installation, and stack replacement. (Reprinted from J. Energ. Storage, 2, Giglio, E. et al., Synthetic natural gas via integrated high-temperature electrolysis and methanation: Part II-Economic analysis, 64–79, Copyright 2015, with permission from Elsevier.)

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The capital, maintenance, and operating costs are higher in co-electrolysis as well. For c­ o-electrolysis, the calculated breakeven electricity price for target and state-ofthe-art scenarios are 67$/MWh and 8 $/MWh, respectively. In addition, the integration of Fischere-Tropsch and high-temperature H2O/CO2 co-electrolysis with SOC processes can efficiently produce syngas to store electricity. Fu et al.13 studied its economic assessment; results show that excess nuclear power and wind power are the preferred electricity sources and that the cost of producing fuels was comparable to the cost of biomass-to-liquid processes.

15.6 SUMMARY In this chapter, the economic analysis of CO2 conversion and the relative added value of various products were discussed based on several typical production cases, including methanol, urea, dimethyl carbonate, formic acid, and syngas. Although the economic feasibility for the production of chemicals/fuels need further verification, it is believed that the costs will decrease further as related technologies are further developed.

REFERENCES



1. Aresta, M., Dibenedetto, A., Quaranta, E. State of the art and perspectives in catalytic processes for CO2 conversion into chemicals and fuels: The distinctive contribution of chemical catalysis and biotechnology. Journal of Catalysis 343, 2–45 (2016). 2. Otto, A., Grube, T., Schiebahn, S., Stolten, D. Closing the loop: Captured CO2 as a feedstock in the chemical industry. Energy & Environmental Science 8, 3283–3297 (2015). 3. Liao, F., Wu, X. P., Zheng, J., Li, M. J., Kroner, A. A promising low pressure methanol synthesis route from CO2 hydrogenation over Pd@Zn core-shell catalysts. Green Chemistry (2016). 4. Rungtaweevoranit, B., et al. Copper nanocrystals encapsulated in Zr-based metalorganic frameworks for highly selective CO2 hydrogenation to methanol. Nano Letters 16, 7645–7649 (2016). 5. Kiss, A. A., Pragt, J. J., Vos, H. J., Bargeman, G., de Groot, M. T. Novel efficient process for methanol synthesis by CO2 hydrogenation. Chemical Engineering Journal 284, 260–269 (2016). 6. Kourkoumpas, D. S., et al. Implementation of the Power to Methanol concept by using CO2 from lignite power plants: Techno-economic investigation. International Journal of Hydrogen Energy 41, 16674–16687 (2016). 7. Wiesberg, I. L., de Medeiros, J. L., Alves, R. M. B., Coutinho, P. L. A., Araújo, O.Q.F. Carbon dioxide management by chemical conversion to methanol: HYDROGENATION and BI-REFORMING. Energy Conversion and Management 125, 320–335 (2016). 8. Pérez-Fortes, M., Schöneberger, J. C., Boulamanti, A., Tzimas, E. Methanol synthesis using captured CO2 as raw material: Techno-economic and environmental assessment. Applied Energy 161, 718–732 (2016). 9. Pérez-Fortes, M., Bocin-Dumitriu, A., Tzimas, E. CO2 utilization pathways: Technoeconomic assessment and market opportunities. Energy Procedia 63, 7968–7975 (2014). 10. Bose, A., Jana, K., Mitra, D., De, S. Co-production of power and urea from coal with CO2 capture: Performance assessment. Clean Technologies and Environmental Policy 17, 1271–1280 (2015).

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11. Kuenen, H. J., Mengers, H. J., Nijmeijer, D. C., van der Ham, A. G. J., Kiss, A. A. Technoeconomic evaluation of the direct conversion of CO2 to dimethyl carbonate using catalytic membrane reactors. Computers & Chemical Engineering 86, 136–147 (2016). 12. Pérez-Fortes, M., Schöneberger, J. C., Boulamanti, A., Harrison, G., Tzimas, E. Formic acid synthesis using CO2 as raw material: Techno-economic and environmental evaluation and market potential. International Journal of Hydrogen Energy 41, 16444–16462 (2016). 13. Fu, Q., et al. Syngas production via high-temperature steam/CO2 co-electrolysis: An economic assessment. Energy & Environmental Science 3, 1365–1608 (2010). 14. Giglio, E., Lanzini, A., Santarelli, M., Leone, P. Synthetic natural gas via integrated high-temperature electrolysis and methanation: Part II-Economic analysis. Journal of Energy Storage 2, 64–79 (2015).

16

Summary and Possible Research Directions for CO2 Conversion Technologies

To facilitate the research and development of CO2 conversion, this book provides a comprehensive overview of advanced CO2 conversion technologies for the production of useful fuels/chemicals. The fundamentals of CO2, including molecule structure, thermodynamics, and kinetics, were summarized to explain its chemical stability, which is a direct obstacle for CO2 conversion. Various conversion technologies as well as enzymatic, mineralization, photochemical/photoelectrochemical, thermochemical, and electrochemical processes were classified and reviewed. Particularly, electrochemical technologies at both low temperatures and high temperatures were considered and compared. Economic feasibilities were analyzed in light of various chemicals/fuels. Finally, technical and application challenges of CO2 conversion to useful fuels/chemicals were proposed. To overcome these challenges, the following future research directions are proposed: 1. Further fundamental understanding of the CO2 activation and conversion processes. The mechanisms of CO2 activation/conversion need to be further studied through both theoretical modeling and experimental testing (especially in electrochemical processes). For theoretical modeling, the transition states and elementary reactions in CO2 conversions need to be further defined, and the rate-limiting step as well as the reaction pathways need to be controlled to overcome conversion barriers. For example, the m ­ echanisms of CO2 reduction and their relationship to reaction active site composition and structures should be fundamentally understood to guide new material development. To mitigate catalyst or electrode material d­ egradation, further fundamental understanding of material behaviors and degradation mechanisms in CO2 conversion processes is of great important. They can be f­ urther revealed by implementing some advanced techniques, for example, in situ time-resolved spectroscopy, X-ray computed tomography (XCT), variable temperature scanning tunneling microscope (VT-STM), low-energy ion scattering spectroscopy (LESI), ambient ­pressure-X-ray photoelectron spectroscopy (AP-XPS), environmental transmission e­ lectron microscopy (TEM), and secondary ion mass spectroscopy (SIMS). For instance, SIMS 297

298

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in a three-dimensional (3D) model can be performed to display elemental 3D distributions with fast oxygen-incorporation paths and separation of electrode/electrolyte interface regions to analyze the causes for degradation and guide new designs of electrodes. To better control the reactions of CO2 conversion kinetically, simulation techniques such as density functional theory (DFT) and molecular dynamics (MD) are needed to calculate energy barriers. With further understanding, it is possible to develop new methods to enhance activity and develop mitigation strategies for degradation. 2. Enhancement of stability, activity, and product selectivity by optimizing or exploring advanced materials. Many investigations have been performed to improve the activity, stability, and product selectivity of CO2 conversion systems, with some progress achieved. However, this technological progress is still insufficient for practical applications. Breakthroughs are needed. Aside from further fundamental understanding and optimization of material performance, structural and morphological tailors of catalyst materials on the nanoscale and the exploration of appropriate innovative materials are also effective methods for enhancing activity, stability, and even product selectivity. For instance, the adsorption and activation of CO2 onto the surface of a catalyst used in photocatalytic/photoelectrochemical processes can be optimized by morphological tailor. The enzymes used in the enzymatic process should be modified and immobilized to reduce the cost and improve activity and stability. With respect to high-temperature electrochemical processes, mixed ionic and electronic conductors (MIECs) and perovskites must be widely studied to improve oxygen electrode performances. For example, the heterostructured perovskite materials can exhibit remarkable enhancements in oxygen reduction reaction (ORR) kinetics, with three orders of magnitude greater than that of previously used materials.1–4 3. Optimizing electrodes, system designs, and reactors for practical applications. Aside from the materials themselves, the major limitations to activity and stability are partially related to operating environments and/or reaction processes, which largely depend on the design of reactors. In addition to improving material stability and activity, improving ­reactor designs and exploring novel appropriate reactors are important for performance enhancements. The CO2 mineralization system mentioned above can be designed to generate electricity and produce industrial valuable products simultaneously, which is economically feasible and environmentally friendly. Regarding the electrochemical process, certain novel designs for solid oxide cell (SOC) configurations can lower ohmic and polarization resistances and enhance the power densities of SOC stacks. Another point is that certain designs for electrolyte membrane-based and gas diffusion electrodes (GDEs) electrochemical cells might be the right approaches to reduce internal resistance and improve reactant mass transfer. 4. Development of CO2 conversion at intermediate temperatures. Although CO2 conversions at low temperatures (800°C) such as SOCs typically can perform with superior product selectivity and efficiency. However, requirements for materials, including electrodes, electrolytes, seals, and interconnects, are much higher, and the stack lifetime needs further verification due to degradation during high-temperature operations. Therefore, to enhance conversion efficiency, product selectivity, and stability, it is vitally important to draw on the strengths of low-temperature and high-temperature processes. It is believed that CO2 conversion at intermediate temperatures (300–700°C) is an important and promising trend, but materials such as catalysts, electrodes, and electrolyte materials need to be developed to fulfill the requirements for CO2 conversion process at intermediate temperatures. 5. Developing the connection between CO2 conversion systems and other clean energy sources. If clean energy sources such as nuclear, solar, wind, geothermal, and so on, are used to run CO2 conversion into useful chemicals/ fuels, CO2 emission and energy shortage issues can be relieved along with providing better economic feasibility. For instance, the conversion of CO2 into valuable fuels (e.g., CH4, CH3OH, HCOOH, etc.) via artificial photosynthesis can be performed using solar energy on a large scale. The coelectrolysis of CO2 and H2O can be performed to produce useful fuels of CO and H2 using solid oxide electrolysis cell stacks running on electricity and heat from redundant nuclear energy. Although efforts have been undertaken to accelerate these developments, wider and scalable applications have a long way to go, with coupling techniques between CO2 conversion systems and other clean energy sources playing a key role. The implementation of this connection is difficult and requires worldwide government support.

REFERENCES

1. Ma, W., et al. Vertically aligned nanocomposite La0.8Sr0.2CoO3 /(La0.5Sr0.5)2CoO4 cathodes- electronic structure, surface chemistry and oxygen reduction kinetics. Journal of Materials Chemistry A 3, 207–219 (2015). 2. Chen, Y., et al. Electronic activation of cathode superlattices at elevated temperatures– source of markedly accelerated oxygen reduction kinetics. Advanced Energy Materials 3, 1221–1229 (2013). 3. Han J. W., Yildiz B. Mechanism for enhanced oxygen reduction kinetics at the (La, Sr) CoO3/(La, Sr)2CoO4+δ heterointerface. Energy & Environmental Science 5, 8598–8607 (2012). 4. Sase, M., et al. Enhancement of oxygen surface exchange at the hetero-interface of (La, Sr) CoO3(La, Sr)2CoO4 with PLD-Layered Films. Journal of The Electrochemical Society 155, B793–B797 (2008).

Index Note: Page numbers in italic and bold refer to figures and tables, respectively. ABO3/A2BO4 in SOCs, heterostructure 189, 192; challenges for 196–8; ORR/OER, mechanism 192–6; oxygen electrodes with 190–1; oxygen exchange kinetics 193 activation energy 15 additives effect 172, 173 AES (Auger electron spectroscopy) 207–8, 208 AFM (atomic-force microscopy) 144, 211, 213 ALD (atomic layer deposition) 198, 245 alkaline earth metal oxides 240 ambient pressure XPS 215 anion exchange membrane (AEM) 52 anisotropic oxygen diffusion 122 anisotropy 194 area specific resistance (ASR) 79, 139, 162, 276 A-site cations segregation: alkaline earth elements 240; in oxidizing atmospheres 227; perovskite-based system 204; Sr-free electrode materials 236–7 ASR see area specific resistance (ASR) atmosphere, effect 227–8 atomic-force microscopy (AFM) 144, 211, 213, 214 atomic layer deposition (ALD) 198, 245 Auger electron spectroscopy (AES) 207–8, 208 Auger spectrum mapping 147 biosyntrolysis 76 blocking effects, Sr segregation 231–3, 234 breadboard regeneration system 74, 75 B-site cations segregation 223, 227; influence 238–9; in perovskite-based system 204; XPS 210 B-site exsolution 238–9 cabin air revitalization 77, 77 Calvin cycle 19, 20 carbonation processes 23–4, 24; indirect pressure 25 carbon mineralization 25 carbon monoxide (CO) 31 catalysts 15; layer 115 cathodic polarization 231, 276 cation: diffusion 279; inter-diffusion 195–6; ­non-stoichiometry 221–3; species 223–4

cation-exchange membrane (CEM) 52 cation segregation: characterization of 204–20; electrochemical activity of SOC electrodes 229–39; ORR/OER activity 239–46; in perovskite-based oxides 221–9; in perovskite-based SOC 203–4 CB (conduction band) 38 cell sealing materials 130, 130–1 ceramic oxygen generator (COG) 79 CFD (computational fluid dynamics) 76 chemical equilibrium co-electrolysis (CEC) model 76 circular disc SOEC stack 262 clean energy sources 299 CO (carbon monoxide) 31 CO2: activation/conversion 297–8; C=O bond energy in 9; conversion, kinetics 14–16; DRM 35–7; electroactive materials for 54; frequencies in 9, 10; hybridization form 10; metal complex geometries 14; mineralization 4, 298; molecular structure 9; with nucleophiles 14; photocatalytic reduction 38, 38, 39; photoelectrocatalytic reduction 41; reduction 5; reforming process 35; solid oxide electrolysis, advantage 75; with space filling model 10, 11; standard Gibbs free-energy 23; thermodynamics 9–13, 11; use and market 288; vibrational modes in 9, 10 CO2 conversion: mineralization process 22–6, 24; photocatalytic and photoelectrochemical process 38–42; thermochemical process 31–7 CO2 conversion and utilization, approaches for 4–6; with enzymes in vitro 21; overall process 22; synthetic processes 4 CO2 emission and reducing 2–3, 3 CO2 hydrogenation: to CH3OH 31–3; to HCOOH 33–5 coal-to-liquids (CTL) process 79 COBRA (coherent Bragg rod analysis) 196, 243 co-catalyst effect 41 coefficient of thermal expansion (CTE) 168

301

302 co-electrolysis 64; see also electrolysis; hightemperature CO2/H2O co-electrolysis/ co-electrolysis (HTCE) coherent Bragg rod analysis (COBRA) 196, 243 computational fluid dynamics (CFD) 76 conduction band (CB) 38 “critical point of phase separation” hypothesis 236, 236 Cr poisoning 278–9 crystallinity, effect 224–5 crystallographic orientations (001)/(100) 83, 83 crystal structure in perovskite oxides 121 CTE (coefficient of thermal expansion) 168 C2 pathway 53–4 Cu catalytic agent 31 current collecting layer 115–16 cycling (1-cell stack) types 96 delamination, oxygen electrode 275–8 dense multilayered structure 189, 192 dense thin-films 189, 192 density functional theory (DFT) 148, 148, 194, 195 Department of Energy (DOE) 76 deposition method 266 detrimental side reactions 234–5 DFT see density functional theory (DFT) dimethyl carbonate (DMC) 291, 291–2, 292 dip coating process 266 direct (single-step) silicide carbonization processes 23 dispersion medium, effect 169–72, 172 dissociation methods 90 DMC see dimethyl carbonate (DMC) DOE (Department of Energy) 76 double perovskites (AA'B2O6-δ): basic structure 122; oxygen transport mechanism 122, 124; typical materials 124, 124 dry reforming of methane (DRM) 35–7 economic analysis 287–8; DMC 291, 291–2, 292; formic acid 292–4, 293; methanol 289–90; syngas 294–5; urea 291, 291 EDS/EDX (energy-dispersive X-ray spectroscopy) 142, 210–11, 280 EIFER (European Institute for Energy Research) 91 EIS (electrochemical impedance spectroscopy) 139 electrical polarization, effect 228–9, 229 electro-active enzyme 21 electrochemical conversion process 5–6; CO2 conversion 49; CO2 reduction via 52; pathways for 50 electrochemical impedance spectroscopy (EIS) 139 electrochemical measurement 139–41, 140

Index electrodes 298; materials/microstructures 113–14, 114 electrolysis: bench-scale system 270, 271; cell, polarization characterization 65; facility in ILS 271; polarization 276; testing conditions 281 electrolyte 128, 128–9, 129 electrolyzers 51 electronic structure 192 electron spectroscopy for chemical analysis (ESCA) 145 elongated thermoelectric fuel cell 85 energetic efficiency 51, 52 Energiewende 90 energy correlation 39, 40 energy-dispersive X-ray spectroscopy (EDS/EDX) 142, 210–11, 280 environmental transmission electron microscopy (ETEM) 216–17, 217 enzymatic conversions, CO2 4, 19–22 ESCA (electron spectroscopy for chemical analysis) 145 ETEM (environmental transmission electron microscopy) 216–17, 217 European Institute for Energy Research (EIFER) 91 exsolution 238 extrusion 265–6 fabrication process: deposition method 266; particulate method 265–6 Faraday efficiency 51, 52 Fischere-Tropsch (F-T) synthesis 57 5-cell stack 261 flat-tubular SOECs 264, 265 focused ion beam (FIB) 142 formic acid (HCOOH) 31, 292–4, 293 Forschungszentrum Jülich 91–2 4 KW high temperature steam electrolysis P&ID 78 freeze casting method: critical factors on morphologies 169–75; ice crystals growth during 170; process/critical factors 168, 169; used in SOCs 167–8 freeze conditions effect 173–4, 174 F-T (Fischere-Tropsch) synthesis 57 fuel electrode: materials 114–18, 115, 117, 119; redox stability 281–2; SiO2 poisoning 279–81 gas chromatograph (GC) 149 gas-to-liquids (GTL) process 79 GHE (greenhouse effect) 86 Gibbs free energy change (ΔG) 11–12, 60 global energy 1–2, 2 graphene-semiconductor photocatalysts 41 Graves' dissertation 81

Index green growth for Germany 91 greenhouse effect (GHE) 86 GTL (gas-to-liquids) process 79 HCOOH generation process 34; reaction process 35; ruthenium dihydride catalyzing 34, 34 HCOO/r-HCOO mechanism 32, 33 heterointerface 197 heterostructure 187–9; ABO3/A2BO4 see ABO3/ A2BO4 in SOCs, heterostructure; application 198; barriers to 197 high-temperature CO2/H2O co-electrolysis/ co-electrolysis (HTCE) 57, 71, 275; kinetics 62–4; methane production by 63; reaction mechanisms 63; SOEC 58; see also HTCE with SOC; system powered by HTGR 99; thermodynamics 58–62, 59, 61; water electrolysis versus CO2 electrolysis 64 high-temperature electrochemical process of CO2 conversion with SOCs: cation segregation, significant phenomenon 203–47; cell and stack design 259–65; characterization 141–8; degradation issues 275–82; fabrication process 265–6; freeze casting method 167–77; heterostructure 187–98; infiltration method 155–67; materials 113–31; measurement 139–41; overview and fundamentals 57–67; research status 71–103; scale-up 266–9; simulation 148–50; SOEC systems 270–1 high-temperature electrolysis in France development 95 HTCE see high-temperature CO2/H2O co-electrolysis/co-electrolysis (HTCE) HTCE with SOC: in China 98–102, 100, 102; in Europe 86–98, 88, 90, 93, 95; in United States 74–86, 82 IEA (International Energy Agency) 1 ILS see integrated laboratory scale (ILS) impregnation technique 155, 167 indirect (multistep) silicide carbonization process 23, 25 infiltration methods 156–7, 157: versus infiltrated electrodes performance 165–6, 166; Ln1-xSrxMO3-δ SOC electrode 157–67; in SOCs 155–6 infiltration precursor 157 influence factors of viscosity 157 infrared (IR) spectroscopy 9 in situ Raman spectroscopy 218–19 in situ resource utilization (ISRU) 71 in situ SIMS 217, 218 in situ XPS 215–16

303 in-situ X-ray fluorescence (XRF) 219, 220 integrated laboratory scale (ILS) 76, 268, 271 interconnect materials 129–30 International Energy Agency (IEA) 1 ion scattering spectroscopy (ISS) 147; see also low-energy ion scattering spectroscopy (LEIS) IR (infrared) spectroscopy 9 ISRU (in situ resource utilization) 71 I–V curves in SOEC/SOFC 88 (La1-xSr x)2CoO4 (LSC) 83, 144; dense thin films 216; heating and cooling cycles 226; -YSZ electrode 160–1, 161 La1-xSr xMnO3-δ (LSM) 157, 158; -infiltrated LSCF cathodes 244; oxygen electrodes 277, 278, 279; -YSZ electrode 157–9, 159, 160 lab-scaled SOEC system 270, 271 LaNi1-xFexO3 (LNF) 237 lattice strain 194–5, 225 layered perovskite 121 LEIS see low-energy ion scattering spectroscopy (LEIS) liquefied natural gas (LNG) 94 low-energy ion scattering spectroscopy (LEIS) 145, 205–7, 206 low-temperature conversion electrochemical methods: catalyst/electrode used in 51–5, 53; electrolyzer used in 51; thermodynamics 49–51, 50, 51 LSCF-YSZ electrode 163–4, 164 LSF-infiltrated YSZ electrode 163 LSF-YSZ electrode 161–3, 162 Massachusetts Institute of Technology (MIT) 80 mass spectrum (MS) 149 MD (molecular dynamics) 83, 148 methanol (CH3OH) 31, 289–90; catalyst systems for 32; reaction mechanisms 33 microstructure characterization: FIB-SEM/XCT 142–4, 143; SEM, TEM/STEM 141–2, 143; STM/STS/AFM 144, 145 MIEC (mixed ionic and electronic conductor) 113, 114 mineralization, CO2 4, 22–6, 24, 26 mixed ionic and electronic conductor (MIEC) 113, 114 mixed ionic/electronic materials 121; double perovskites (AA'B2O6-δ) 122–4; perovskites (ABO3±δ) 120–2; Ruddlesden-Popper (A2BO4+δ) 124–7 molecular dynamics (MD) 83, 148 molecular structure, CO2 9 MS (mass spectrum) 149 multi-module SOEC electrolyzer installation 268, 269

304 multiple cell stack 267 multiple-step infiltration process 156 multi-stack testing 76 NADH (nicotinamide adenine dinucleotide) 21–2 NADPH (nicotinamide adenine dinucleotide phosphate) 19 next-generation hybrid system 76, 77 Ni-based catalysts 35–6 nicotinamide adenine dinucleotide (NADH) 21–2 nicotinamide adenine dinucleotide phosphate (NADPH) 19 Ni-YSZ cermet, three-dimensional structure 115 Ni/YSZ fuel electrode 280, 281 nuclear magnetic resonance (NMR) spectroscopy 9 nucleation theory 279 nucleophiles 14 one-dimensional chemical equilibrium model 76 open circuit voltages (OCVs) 139 organometallic complexes 41 ORR/OER activity: A-site segregation 236–7; B-site segregation 238–9; for perovskite electrodes 239–46; Sr segregation 230–6 ORR/OER, mechanism: anisotropy 194; cation inter-diffusion 195–6; electronic structure 192; lattice strain 194–5; LSC113 and LSC214 layers 194 oxygen electrode(s): ABO3/A2BO4 interface 190–1; Cr poisoning 278–9; delamination 275–9; issues 127–8; materials 119–27; reaction mechanism 119 oxygen evolution reaction (OER) 83; see also ORR/OER activity; ORR/OER, mechanism oxygen exchange kinetics 193 oxygen reduction reaction (ORR) 81, 84, 120; see also ORR/OER activity; ORR/ OER, mechanism particulate method 265–6 PEMFCs (proton exchange membrane fuel cells) 51 perovskite-based SOC electrodes 203–4 perovskite electrodes: alkaline earth metal oxides 240; less active phase 245–6; secondary perovskite-based phase 242–5; transition metal cations 240–2 perovskite oxides, cation segregation in: atmosphere effect 227–8; cation nonstoichiometry 221–3; cation species 223–4; crystallinity 224–5; electrical polarization effect 228–9, 229; influencing factors 221, 222; lattice strain 225; temperature effect 225–7; thermal history 225–7

Index perovskites (ABO3±δ): basic structure 120–1; oxygen transport mechanism 121, 121–2; typical materials 122 photocatalysis/photoelectrochemical process 38–42 photon absorption 21 photosynthesis process 19, 20 planar SOEC 260–1 plasma spraying 266 PLD (pulsed laser deposition) 211, 241 polyvinyl alcohol (PVA) 172 porous composite structure 189, 192 porous fuel electrodes 114 porous infiltrated structure 189, 192 porous layered structure 189, 192 power-to-gas (P2G) storage 90 power to methanol (PtM) 289, 290 Pr(Ni, Mn)O3 (PNM) 245 product analysis, CO2 149–50 product gas composition 92 product selectivity, CO2 conversions 298 proton exchange membrane fuel cells (PEMFCs) 51 PtM (power to methanol) 289, 290 pulsed laser deposition (PLD) 211, 241 PVA (polyvinyl alcohol) 172 Raman spectroscopy 218, 220 RAXR (resonant anomalous X-ray reflectivity) 218 reaction pathway energy diagrams 15, 15 redox stability, fuel electrode 281–2 relative added value of chemicals/fuels 287–8, 289 renewable-to-liquids (RTL) process 79 resonant anomalous X-ray reflectivity (RAXR) 218 resonant soft x-ray reflectivity (RXR) 218 reverse water-gas shift (RWGS) mechanism 32, 91 rhodium (Rh) complex 21 Risø National Laboratory (RNL) 87 RTL (renewable-to-liquids) process 79 Ruddlesden-Popper (A2BO4+δ) 113; basic structure 124; oxygen transport mechanism 124–5, 125; phase 84; typical materials 125–7 RWGS (reverse water-gas shift) mechanism 32, 91 RXR (resonant soft x-ray reflectivity) 218 samaria doped ceria (SDC) 79, 159 scale-up, SOEC 266–9 scanning electron microscope (SEM) 141, 141, 208, 208, 214, 224 scanning electron microscopy-focused ion beam (SEM-FIB) 81, 82

305

Index scanning transmission electron microscope (STEM) 142, 210, 210–11 scanning tunneling microscope (STM) 40, 144, 144, 211–14 scanning tunneling spectroscopy (STS) 144, 212 SDC (samaria doped ceria) 79, 159 secondary ion mass spectroscopy (SIMS) 211 secondary perovskite-based phase 242–5 SEM see scanning electron microscope (SEM) SEM-FIB see scanning electron microscopyfocused ion beam (SEM-FIB) semiconductor materials 38–9 semiconductor photocatalysts 39 SIMS see secondary ion mass spectroscopy (SIMS) single cell tests development 93 SiO2 poisoning 279–81 SOCs see solid oxide cells (SOCs) SOECs see solid oxide electrolysis cells (SOECs) solid oxide cells (SOCs) 49, 57–8, 113, 155, 187–8; constant-current electrolysis test/reversible cycling test 89; material selection and components 64–7; microstructures 66; simplified system 80 solid oxide electrolysis cells (SOECs) 57–8, 71, 97; cell configurations 260; charge transport in 279; components 259; fuel production and energy storage in Denmark 86; microstructure 64; perovskite-based oxygen electrode materials in 123; requirements for 67; RP phase oxides in 126; singlecell 259; stacks 259–65; system management 270 solid oxides, fluorite structure 85 solids loading effect 175, 176, 177 spray pyrolysis 266 sputtering process 266 Sr2FeMo0.65Ni0.35O6-δ (SFMNi) fuel electrode 118 Sr-free electrode materials, A-site segregation on 236–7 Sr segregation 207, 230–1; active phases generation 235–6; blocking effects 231–4; detrimental side reactions 234–5; Sr-enriched surface phase 232; surface 220 SrTi1-xFexO3 (STFx) system 232 SSC-infiltrated electrodes 164–5, 165 STEM see scanning transmission electron microscope (STEM) STM see scanning tunneling microscope (STM) strategic electrochemistry research center (SERC) 87, 87 STS (scanning tunneling spectroscopy) 144, 212 SunFire GmbH 267, 269

super-dry reforming process using Ni/MgAl2O4 36, 37 surface analysis 145–8, 146 surface cation segregation: AES 207–8, 208; AFM 211, 213; EDS/EDX 210–11; ETEM 216–17; LEIS 205–7; Raman spectroscopy 218–19; RAXR 218, 219; RXR 218; SEM 208, 208; SIMS 211; in situ Raman spectroscopy 218–19; in situ SIMS 217, 218; in situ XPS 215–16; in situ XRF 219, 220; STEM 210–11; STM 211–14; structure and composition 205; surface sensitive technologies 205; XPS 209–10; XRD 214 surface chemistry 83 surface decoration 242; with alkaline earth metal oxides 240; by less active phase 245–6; by secondary perovskite-based phase 242–5; of transition metal cations 240–2 surface sensitive technologies 205 syngas 57, 86, 294–5 tape calendering/casting process 265 TCD (thermal conductivity detector) 149 TEC (thermal expansion coefficient) 155 TEM (transmission electron microscopy) 141 temperature: CO2 conversions 298–9; effect, cation segregation 225–7 10-cell stack 261 theoretical modeling, CO2 conversions 297 thermal conductivity detector (TCD) 149 thermal expansion coefficient (TEC) 155 thermal history effect, cation segregation 225–7 thermocatalytic process 31 thermochemical conversion reaction 31, 32 thermodynamics 9–13; heat and equilibrium constants 13; HTCE 58–62, 59, 61; low-temperature conversion electrochemical methods 49–51, 50, 51; parameters 11, 12 three-dimensional CFD models 76 3D X-ray microscopy image 102 three-phase boundary (3PB) 113 time-resolved infrared rectroscopy (TRIR) 40 transition metal cations 240–2 transmission electron microscopy (TEM) 141 triple phase boundaries (TPB) 115 TRIR (time-resolved infrared rectroscopy) 40 tubular configurations 259 tubular SOEC 261, 263, 264, 264 two-phase boundary (2PB) 113 urea (NH2CONH2) 291, 291 vacancy mechanism 121–2 value-added mineral products 25

306 vertically aligned nanocomposite structures 189, 192 Virkar’s approach 275 water gas shift (WGS) 149; reaction 60, 62 weak acids 25 Westinghouse Research Laboratories 74 WGS see water gas shift (WGS)

Index XPS see X-ray photoelectron spectroscopy (XPS) X-ray computed tomography (XCT) 142, 143 X-ray diffraction (XRD) 214 X-ray photoelectron spectroscopy (XPS) 145, 209, 209–10 XRF (in-situ X-ray fluorescence) 219, 220 yttria-stabilized zirconia (YSZ) 71; -Ni/interface 282