Oomman K. Varghese, PhD, is an Associate Professor in the Department of Physics, Researcher at Texas Center for Superconductivity and Leader of Nanomaterials and Devices Laboratory at the University of Houston. In 2011, Thomson Reuters ranked him 9th among "World's Top 100 Materials Scientists" in the previous decade.

Flavio L. Souza, PhD, is the Lead Researcher and Coordinator of Green Hydrogen Program of Brazilian Center for Research in Energy and Materials (CNPEM), Associate Professor at Federal University of ABC and an accredited researcher by CNPq (The Brazilian Research Council). He received an Academic Excellence award (2017) from Federal University of ABC for his achievements in research and dedication to higher education.

List of Contributors xiii Preface xvii 1 Solar Fuel Generation: The Relevance and Approaches 1Ingrid Rodriguez-Gutierrez, Flavio L. Souza, and Oomman K. Varghese 1.1 Introduction 1 1.2 The Nexus Between Fossil Fuels, Global Warming, and Climate Change 2 1.3 The Energy System Transformation 4 1.4 Solar Fuels 5 1.5 Solar Reduction of CO 2 forFuelProduction 6 1.6 Solar Water Splitting for H 2 Generation 7 1.7 Solar to Fuel Conversion Pathways 8 1.7.1 Bioconversion 8 1.7.2 Thermoconversion 9 1.7.3 Electroconversion 10 1.7.4 Photoconversion 12 1.8 Conclusion 13 References 13 Section 1 Solar Fuel Generation Processes: Science and Technology 19 2 Introduction to Photocatalytic/Photoelectrochemical Fuel Generation: Science and Technology Perspective 21Ke Fan, Lei Wang, and Lianpeng Tong 2.1 Introduction 21 2.2 The Natural Photosynthetic Water Splitting and CO 2 Reduction 22 2.2.1 Oxygen-Evolving Complex (OEC) 22 2.2.2 Hydrogenase 23 2.2.3 Enzymes that Reduce CO 2 24 2.3 Artificial Systems for Solar-Driven Chemical Fuels Production 25 2.3.1 Bioinspired Synthetic Systems 25 2.3.1.1 Synthetic Molecular Catalysts 25 2.3.1.2 Application of Synthetic Model Compounds in PEC Cells 26 2.3.2 Bioinorganic Hybrid Systems 26 2.3.3 Photoelectrochemical Water Splitting and CO 2 Reduction 27 2.3.3.1 Some Basic Concepts of Semiconductors 27 2.3.3.2 Photoelectrochemical (PEC) Water Splitting 29 2.3.3.3 Configurations of PEC Cell for Water Splitting 33 2.3.3.4 A Few Semiconductors Extensively Studied for Water Splitting 34 2.3.3.5 Photoelectrochemical (PEC) CO 2 reduction 35 2.3.3.6 Particulate Photocatalytic Systems for Water Splitting/CO 2 Reduction 37 2.4 Challenges and Outlook 39 References 40 3 Solar Thermochemical Fuels 47Christoph Falter Nomenclature 47 3.1 Thermodynamics 48 3.2 Solar Thermochemical Processes and Reactor Concepts 49 3.2.1 Thermolysis of H 2 O 49 3.2.2 H 2 /CO From H 2 O/CO 2 Using Thermochemical Cycles 50 3.3 Energy and Mass Balance 54 3.3.1 Thermochemical Reactor 54 3.3.2 Energy and Mass Balance of Solar Thermochemical Fuel Plant 55 3.3.3 Possibilities of Enhancing Plant Efficiency 57 3.4 Techno-Economic Analysis 58 3.4.1 System Description 59 3.4.2 Economic Model 59 3.4.3 Production Costs 60 3.4.4 Comparison with Other Alternative Fuel Pathways 62 3.5 Life-Cycle Analysis 63 3.5.1 Goal and Scope 63 3.5.2 Inventory Analysis 64 3.5.3 Impact Assessment 64 3.5.4 Interpretation 65 3.5.4.1 Scenario Analysis-CO 2 From Natural Gas Combustion 65 3.5.4.2 Scenario Analysis-Grid Electricity 65 3.5.4.3 Comparison with Published GWP Values of Other Fuel Pathways 66 3.6 Land and Water Demand 67 3.6.1 Water Footprint 67 3.6.2 Land Demand 69 3.7 Geographical Potential 71 3.7.1 Determination of Suitable Areas for Solar Thermochemical Fuel Production 71 3.7.2 Determination of Life-Cycle Production Costs 73 3.7.3 Production Cost 74 3.8 Conclusions 76 References 77 4 Principles, Operations, and Techno-Economics of Photovoltaic-Electrolysis and Photoelectrochemical Water Splitting Processes 83Nicolas Gaillard 4.1 Introduction 83 4.2 The Solar-to-Hydrogen Conversion Process 85 4.2.1 Fundamental Concepts 85 4.2.2 Material and Device Considerations 86 4.3 PV-Electrolysis Water Splitting 88 4.3.1 The Photovoltaic Process 88 4.3.2 Fundamentals of Water Electrolysis 91 4.3.3 PV-E Operating Principles 93 4.3.4 Evolution of PV-E Systems and Current State-of-the-Art 94 4.3.4.1 PV-E Systems with Planar Photovoltaics 94 4.3.4.2 PV-E Systems with Concentrated Photovoltaics 96 4.4 Photoelectrochemical Water Splitting 97 4.4.1 Energetics of the Semiconductor/Liquid Junction 97 4.4.2 Charge Transfer Dynamics at the Semiconductor/Liquid Junction 99 4.4.3 Current-Potential Behavior of a Photoelectrode 100 4.4.4 Spontaneous Water Splitting with Multi-Junction PEC Devices 103 4.5 Techno-Economics of PV-E and PEC Water Splitting 107 4.5.1 Similarities and Differences Between PV-E and PEC Water Splitting Technologies 107 4.5.2 Independent Assessments of PEC Technologies 108 4.5.3 Independent Assessments of PV-E Technology 110 4.5.4 Comparative Assessments of PV-E and PEC Technologies 110 4.6 Conclusion and Outlook 111 Acknowledgments 112 References 113 5 A Brief History of Molecular Photosynthesis: The Quest for the Bridge Between Light and Chemistry 119Liniquer A. Fontana, Vitor H. Rigolin, Catia Ornelas, and Jackson D. Megiatto Jr. 5.1 Introduction 119 5.2 Historical Context and Early Findings 119 5.3 The Beginning of the Modern Understanding of Photosynthesis 121 5.4 Molecular Photosynthesis: Human Ingenuity Enters the Game 123 5.4.1 Biomimetic Reaction Centers 123 5.4.2 Artificial Reaction Centers with Nonnatural Electron Donors and Acceptors 126 5.4.3 Supramolecular Assembly of Artificial Reaction Centers 128 5.4.4 Artificial Antenna 131 5.4.5 Photo-Regulation 132 5.4.6 Artificial Reaction Centers Thermodynamically Poised to Oxidize Water 134 5.5 Harvesting the Energy of Charge-Separated States for Solar Fuel Production 137 5.5.1 Solar-Sensitized Photoelectrochemical Cells 137 5.5.2 Artificial Leaf 138 5.6 Conclusions 139 References 139 6 The Competitive Kinetics of Solar-Driven CO 2 Reduction 143Mark T. Spitler 6.1 Introduction 143 6.2 Photosynthetic Systems 144 6.2.1 General 144 6.2.2 PSII Coupling to the OEC 146 6.2.3 PSI Coupling to PSII and RuBisCO 148 6.2.4 LHC Coupling 149 6.2.5 Indirect Coupling to RuBisCo 149 6.2.6 Photostability 150 6.3 Water Oxidation 151 6.3.1 Molecular Water Oxidation 152 6.3.2 Dye-Sensitized Photoelectrosynthesis Cell (DSPEC) 154 6.3.3 Photoelectrochemical (PEC) Water Splitting 158 6.3.4 Particles 160 6.4 CO 2 Reduction 163 6.4.1 Recycling Applications 163 6.4.2 Metals as Catalysts 164 6.4.3 PV-Driven CO 2 Reduction 166 6.4.4 Solar Fuel Harvesting 167 6.4.5 Semiconductor Photoanode-Driven Reduction of CO 2 at Metals 167 6.4.6 Semiconductor Electrodes 167 6.4.7 Reduction of CO 2 at Semiconductor Surfaces 169 6.4.8 Molecular Catalysts 171 6.4.9 Particles for CO 2 Reduction 172 6.5 Conclusions 174 References 175 7 Utilizing the Band Diagram Framework to Interpret the Operation of Photoelectrochemical Cells 183Kirk H. Bevan, Botong Miao, and Asif Iqbal 7.1 Semiconductor Concepts 183 7.2 Semiconductor-Liquid Junctions in the Dark 186 7.2.1 Charge Equilibration in the Dark 187 7.2.2 Semiconductor-Liquid Junctions Under Bias in the Dark 188 7.2.3 Biasing with Respect to Reference Electrodes 190 7.3 Illuminated Semiconductor-Liquid Junctions 190 7.3.1 Gartner's Model 190 7.3.2 Peter's Model 193 7.4 The Role of Numerical Modeling 194 7.4.1 Semiclassical Approach 194 7.4.2 Insights from Semiclassical Modeling 197 7.5 Outlook 200 References 200 Section 2 Materials for Solar Fuel Generation 203 8 Materials Used for Solar Thermal/Thermochemical Processes for CO 2 /H 2 O Dissociation/Conversion 205Heng Pan, Youjun Lu, and Bingchan Hu 8.1 Introduction 205 8.2 Solar Thermolysis of H 2 OorCO 2 205 8.3 Redox Pairs for Two-Step Thermochemical Cycles 206 8.3.1 Volatile Redox Pairs 207 8.3.1.1 ZnO/Zn Pair 207 8.3.1.2 SnO 2 /SnO Pair 209 8.3.2 Nonvolatile Redox Pairs 209 8.3.2.1 Fe 3 O 4 /FeO Pair 209 8.3.2.2 CeO 2 /CeO 2¿¿ Pairs 210 8.3.2.3 CoFe 2 O 4 /FeAl 2 O 4 Pairs 211 8.3.2.4 Perovskites 211 8.3.3 Redox Pairs: New Discoveries 212 8.4 Materials for Sulfur-Iodine (S-I) Cycle 213 8.4.1 Corrosion-Resistant Materials 214 8.4.2 The Catalysts of HI Decomposition 214 8.4.3 The Catalysts for H 2 SO 4 Decomposition 217 8.5 Other Multi-Step Thermochemical Cycles 218 8.6 Catalysts for Solar Gasification and Reforming 220 8.6.1 Catalysts for Solar Gasification 220 8.6.2 Catalysts for Solar Reforming of Methane 220 8.6.3 Catalysts for Solar Reforming of Methanol 221 8.7 Summary and Outlook 222 Acknowledgment 222 Conflict of Interest 222 References 222 9 Electrocatalytic Reduction of CO 2 to Value-Added Chemicals and Fuels 233Qian Sun, Kamran Dastafkan, and Chuan Zhao 9.1 Introduction 233 9.2 Fundamentals of CO 2 Electroreduction (CO 2 RR) 235 9.2.1 Reaction Mechanism of CO 2 RR 235 9.2.2 Electrochemical Cells 237 9.2.2.1 H-Cell 237 9.2.2.2 Flow Cell 240 9.2.2.3 Mea 241 9.2.2.4 High-Temperature Molten Salt Cell 242 9.2.2.5 Solid Oxide Cell 242 9.2.3 Electrolytes 243 9.3 Electrocatalysts for CO 2 RR 244 9.3.1 Metals 245 9.3.1.1 Noble Metals 245 9.3.1.2 Transition Metals 247 9.3.1.3 Oxide-Derived Metals 248 9.3.1.4 Metal Alloys 248 9.3.2 Metal Compounds 250 9.3.2.1 Metal Chalcogenides 250 9.3.2.2 Metal Oxides 252 9.3.2.3 Metal Nitrides 253 9.3.2.4 Metal Hydroxides 254 9.3.3 Single-Atom Catalysts 254 9.3.3.1 Noble Metal SACs 254 9.3.3.2 Transition Metal SACs 255 9.3.3.3 Other Metal SACs 256 9.3.4 Molecular Catalysts 257 9.3.4.1 Organometallic Complexes 257 9.3.4.2 MOF and COF Catalysts 258 9.3.4.3 Metal-Free and Polymerized Catalysts 259 9.4 In Situ Characterizations of Electrocatalysts for CO 2 RR 260 9.4.1 In Situ Raman 260 9.4.2 In Situ UV-vis Spectroscopy 262 9.4.3 In Situ FTIR Spectroscopy 262 9.4.4 Operando XAS 263 9.5 Summary and Perspectives 264 9.5.1 Challenges for CO 2 RR 265 9.5.2 Comparison with HER 265 9.5.3 Perspectives for CO 2 RR 265 References 269 10 Ceramic Materials for Photocatalytic/Photoelectrochemical Fuel Generation 285Appu V. Raghu and Takashi Tachikawa 10.1 Introduction 285 10.2 Photocatalytic/Photoelectrochemical Fuel Generation 285 10.2.1 Photon Absorption 288 10.2.2 Requirements of Materials Useful as Photocatalysts 289 10.3 Metal Oxides as Photocatalysts 290 10.3.1 Doping and Surface Treatments 291 10.3.2 Long-Term Stability 292 10.3.3 Heterostructures 292 10.4 Other Ceramic Materials 295 10.4.1 Nitrides 295 10.4.2 Oxynitrides 296 10.4.3 Carbides 296 10.4.4 MXenes 297 10.5 Challenges 301 10.6 Conclusion 301 References 301 11 Gallium Nitride-Based Artificial Photosynthesis Integrated Devices for Solar Hydrogen Generation and Carbon Dioxide Reduction 309Baowen Zhou, Peng Zhou, Wanjae Dong, and Zetian mi 11.1 Introduction 309 11.2 Merits of III-Nitride Nanostructures for Artificial Photosynthesis 310 11.3 Recent Advances...