Contents

Author Biographies xix

Chapter 1 The Potential Contribution of Photoelectrochemistry in theGlobal Energy Future 1Bruce Parkinson and John Turner

1.1 History 11.2 Solar Hydrogen 31.3 New Materials 81.4 Commercial Viability of Photoelectrolysis as a Route

to Hydrogen 11

1.5 Photoelectrochemical Reduction of Carbon Dioxide 121.6 Summary and Conclusions 16Acknowledgement 17References 17

Chapter 2 Kinetics and Mechanisms of Light-Driven Reactions atSemiconductor Electrodes: Principles and Techniques 19Laurence Peter

2.1 Introduction 192.2 Conventional and Nanostructured Photoelectrodes 20

2.2.1 Conventional Semiconductor Electrodes 202.2.2 Potential and Charge Distribution at the

Semiconductor-Electrolyte Junction 202.2.3 Collection of Minority Carriers at the

Illuminated Semiconductor-ElectrolyteJunction 22

2.2.4 Nanostructured and Mesoporous Electrodes 23

RSC Energy and Environment Series No. 9

Photoelectrochemical Water Splitting: Materials, Processes and Architectures

Edited by Hans-Joachim Lewerenz and Laurence Peter

r The Royal Society of Chemistry 2013

Published by the Royal Society of Chemistry, www.rsc.org

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2.3 Rate Constants and Reaction Orders 252.3.1 Electrode Kinetics at Metal Electrodes 252.3.2 Kinetics of Minority Carrier Reactions at

Semiconductor Electrodes 262.3.3 The Concept of Overpotential for Minority

Carrier Reactions 292.3.4 Competition between Charge Transfer and

Recombination 302.4 Determination of Rate Constants from Transient

Photocurrents 34

2.5 Intensity-Modulated Photocurrent Spectroscopy 362.6 Photoelectrochemical Impedance Spectroscopy 402.7 Following Interfacial Electron Transfer using

Microwave Reectivity Measurements 42

2.8 Potential and Light-Modulated Absorption

Spectroscopy 47

2.9 Conclusions and Outlook 49Acknowledgements 49References 49

Chapter 3 Structured Materials for Photoelectrochemical WaterSplitting 52James MCKone and Nathan Lewis

3.1 Introduction 523.2 Interplay between Materials Properties and Device

Characteristics 53

3.2.1 Light Absorption and Collection ofPhotogenerated Carriers in CrystallineSemiconductors 54

3.2.2 Open-Circuit Photovoltage at StructuredSemiconductors 59

3.2.3 Electrochemical Transport at StructuredSemiconductors 61

3.2.4 Catalysis at Structured Semiconductors 633.2.5 Outlook 64

3.3 Review of Recently Demonstrated Advantages of

Structured Materials for Photoelectrochemical Water

Splitting 64

3.3.1 Metal Oxide Photoelectrodes 653.3.2 High Aspect-Ratio Structures 693.3.3 Water Splitting by Colloidal Particles 713.3.4 Water Splitting Catalysis by Structured

Materials 71

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3.3.5 Advances in Modeling HeterogeneousCatalysis 74

3.3.6 Broader Considerations Beyond Small 75Acknowledgements 76References 76

Chapter 4 Tandem Photoelectrochemical Cells for Water Splitting 83Kevin Sivula and Michael Gratzel

4.1 Introduction and Motivation for Using Multiphoton

Systems 83

4.2 Strategies and Limitations of Multi-Absorber Systems 854.2.1 Brute Force Strategies 854.2.2 The Tandem Cell Concept 864.2.3 The D4 Strategy and its Potential 874.2.4 D4 Device Architectures 91

4.3 PV/PV Strategies 914.4 Photoelectrode/PV Systems 93

4.4.1 Advantages and Operation of a Photoanode/PV Tandem Cell 93

4.4.2 Photoanode/PV Examples 954.4.3 The Photoanode/DSSC Tandem Cell 96

4.5 Photoanode/Photocathode Systems 1004.6 Practical Device Design Considerations 1024.7 Summary and Outlook 104Acknowledgement 105References 105

Chapter 5 Particulate Oxynitrides for Photocatalytic Water SplittingUnder Visible Light 109Kazuhiko Maeda and Kazunuri Domen

5.1 Introduction 1095.2 Oxynitrides Having Early-Transition Metal Cations 1125.3 Improvement of Water Reduction Activity of

d0-(Oxy)nitrides 114

5.4 Ge3N4, a Typical Metal Nitride with d10 Electronic

Conguration 117

5.5 GaN-ZnO and ZnGeN2-ZnO Solid Solutions 1185.6 Two-Step Water Splitting Mimicking Natural

Photosynthesis in Green Plants 123

5.7 Photoelectrochemical Water Splitting Using

d0-Oxynitrides 124

5.8 Conclusions 128References 128

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Chapter 6 Rapid Screening Methods in the Discovery and Investigationof New Photocatalyst Compositions 132Allen Bard, Heung Chan Lee, Kevin Leonard,

Hyun Seo Park and Shijun Wang

6.1 Introduction 1326.2 Rapid Synthesis on Arrays 1346.3 Rapid Screening with SECM 137

6.3.1 Method 1376.3.2 Guidelines 1416.3.3 Data Analysis 144

6.4 Rapid Screening with Electrocatalysts 1456.5 Follow-Up Studies with Large Electrodes 1486.6 Correlation of Doping Eects and Theory 149References 150

Chapter 7 Oxygen Evolution and Reduction Catalysts: Structural andElectronic Aspects of Transition Metal Based Compoundsand Composites 154Sebastian Fiechter and Peter Bogdano

7.1 Introduction 1547.1.1 Chemical Energy Storage 1557.1.2 Oxidation and Reduction Catalysts

in Nature 1567.2 Oxygen Evolving Catalysts an Inorganic

Approach 161

7.2.1 Structural Features 1637.2.2 Preparation Routes and Phase

Formation 1657.2.3 Electrochemical Behavior and

Structure-function Analysis 1687.3 Functionalization of Electrode Surfaces and

In-Operando studies 178

7.3.1 In-Line Synchrotron Radiation X-rayPhotoelectron Spectroscopy 179

7.3.2 In-Situ X-ray Absorption Spectroscopy 1807.4 Integrated Concepts and Challenges in Catalysts

Characterization 186

7.5 Summary and Outlook 189Acknowledgements 190References 190

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Chapter 8 The Group III-Nitride Material Class: from Preparation toPerspectives in Photoelectrocatalysis 193Ramon Collazo and Nikolaus Dietz

8.1 Introduction 1938.1.1 Properties of the Binaries InN, GaN, AlN and

their Ternaries 1948.1.2 Band Gap Alignments for InN-GaN-AlN-InN

Alloys and Heterostructures 1958.2 Fabrication of Epitaxial Alloys and Heterostructures 197

8.2.1 Epitaxial Growth Techniques 1978.2.2 Substrate Issues 199

8.3 The AlxGa1-xN System: from the Binaries to Ternary

Alloys and Heterostructures 200

8.3.1 Properties of Epitaxial GaN-AlN Alloys 2008.3.2 Ternary AlGaN Alloys and Heterostructures 2038.3.3 Point Defects in AlGaN Alloys: Electrical

Properties 2068.4 The InxGa1-xN System 209

8.4.1 Gallium-rich Ternary InGaN Alloys andHeterostructures 209

8.4.2 InN and Indium-Rich InGaN Epilayers andHeterostructures 210

8.5 Present Challenges in Materials Improvement and

Materials Integration 214

8.6 InGaN-based Photoelectrochemical Cells for

Hydrogen Generation 216

8.7 Conclusions 217Acknowledgement 218References 218

Chapter 9 Epitaxial III-V Thin Film Absorbers: Preparation, EcientInP Photocathodes and Routes to High Eciency TandemStructures 223Thomas Hannappel, Matthias M May and

Hans-Joachim Lewerenz

9.1 General Introduction 2239.2 Introduction to III-V Materials 2249.3 Epitaxial III-V Systems for Solar Energy

Conversion 225

9.3.1 Eciency Considerations and Multi-JunctionAbsorbers 225

9.3.2 Band Alignment 227

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9.3.3 Water Splitting with III-V Semiconductors 2299.3.4 III-V Heteroepitaxy 230

9.4 Preparation of Epitaxial III-V Thin Film Absorbers

Using Optical In Situ Control 231

9.4.1 Optical In Situ Control: ReectanceAnisotropy Spectroscopy 231

9.4.2 Metal-Organic Chemical Vapor Deposition 2329.5 InP(100) Absorbers: Heterostructures and

Photocathodes 235

9.5.1 InP-based Heterostructures 2359.5.2 Surface-Functionalized InP(100) for

Ecient Hydrogen Evolution 2369.6 GaP(100) and Hetero-Interfaces 249

9.6.1 GaP Preparation 2509.6.2 Interface Formation with Water 2519.6.3 The GaP(N,As)/Si Tandem System 2539.6.4 Micro- and Nanostructured Systems 254

9.7 Synopsis 258Acknowledgements 259References 259

Chapter 10 Photoelectrochemical Water Splitting: A First PrinciplesApproach 266Anders Hellman

10.1 Introduction 26610.2 Capture of the Photon 268

10.2.1 Band Gap Design 26910.2.2 Plasmon-Assisted Photon Absorption 271

10.3 ElectronHole Separation 27210.4 Charge Transfer 27710.5 Surface Reaction (Electrochemical Conversion) 279

10.5.1 Pourbaix Surface Diagrams 28010.5.2 Reaction Mechanism 28110.5.3 Overpotential 282

10.6 Conclusion and Outlook 284Acknowledgements 284References 284

Chapter 11 Electro- and Photocatalytic Reduction of CO2:The Homogeneous and Heterogeneous Worlds Collide? 289David Boston, Kai-Ling Huang, Norma de Tacconi, Noseung

Myung, Frederick MacDonell and Krishnan Rajeshwar

11.1 Introduction and Scope 289

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11.2 Thermodynamics of CO2 Reduction 29911.3 Energetics of CO2 Reduction 299

11.3.1 General Remarks 29911.3.2 Band Energy Positions of Selected Oxide

Semiconductors and CO2 Redox Potentials 30011.3.3 Molecular Orbital Energy Diagram for

Ru(phen)321 Compared with CO2 Redox

Potentials 30111.4 Electrocatalytic CO2 Reduction with Molecular

Catalysts 301

11.4.1 Pyridine for Electrocatalytic Reduction of CO2 30211.4.2 Rhenium Polypyridyl Complexes for

Electrocatalytic Reduction of CO2 30311.4.3 Ruthenium Polypyridyl Complexes for

Electrocatalytic Reduction of CO2 30511.5 Electrocatalytic Materials Inspired by Fuel Cell

Electrode Nanocomposites 306

11.5.1 Pt-carbon Black-TiO2 NanocompositeFilms Containing Highly Dispersed PtNanoparticles as Applied to CO2Electroreduction 306

11.6 Transition Metal Complexes for Photocatalytic CO2Reduction 313

11.6.1 Catalysts for Reduction of CO2 to CO orHCOO 313

11.6.2 Deeper Reduction Using a Hybrid System 31711.7 Photocatalytic CO2 Reduction using Semiconductor

Nanoparticles 320

11.7.1 Syngas as Precursor in Fisher-TropschProcess for Production of Synthetic Fuels 320

11.7.2 Photogeneration of Syngas UsingAgBiW2O8 Semiconductor Nanoparticles 320

11.7.3 Photoreduction of CO2 using Cu2O asSemiconductor and Pyridine as SolutionCo-Catalyst 321

11.8 Concluding Remarks and Future Directions 325Acknowledgements 326References 326

Chapter 12 Key Intermediates in the Hydrogenation and ElectrochemicalReduction of CO2 333Klaas Jan Schouten and Marc Koper

12.1 Introduction 333

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12.2 CO2 Fixation in the Calvin Cycle 33512.3 The Mechanisms of CO2 Reduction Using

Heterogeneous Catalysis 336

12.3.1 Carbon Monoxide Synthesis via the ReverseWater-Gas Shift Reaction 336

12.3.2 Methanation of Carbon Dioxide 33712.3.3 Methanol Synthesis 33812.3.4 Synthesis of Hydrocarbons 339

12.4 The Mechanisms of CO2 Reduction Using

Homogeneous Catalysis 340

12.4.1 Synthesis of Formic Acid 34012.4.2 Synthesis of Other Products 341

12.5 Mechanisms of the Electrochemical Reduction

of CO2 342

12.5.1 Homogeneous Electrocatalysis 34312.5.2 Heterogeneous Electrocatalysis 34612.5.3 Photoelectrochemical CO2

Reduction 35112.6 Discussion and Conclusions 352References 354

Chapter 13 Novel Approaches to Water Splitting by Solar Photons 359Arthur J. Nozik

13.1 Introduction and Previous History of

Photoelectrochemical Water Splitting/

Photoelectrolysis 359

13.2 Detailed Balance Thermodynamic Calculations of

Solar Water-Splitting PCEs 365

13.2.1 Conventional Solar Cells at One SunIntensity 365

13.2.2 Tandem Semiconductor Structures forWater Splitting 367

13.2.3 Power Conversion Eciencies Based onUtilization of Hot Electron-Hole Pairs andSinglet Fission 369

13.3 Buried Junctions and Other Novel Approaches 37913.3.1 Buried p-n Junctions in a Tandem Cell 37913.3.2 Buried p-n Junctions in a Texas Instruments

System for H2O Splitting 38213.3.3 Buried p-n Junctions using Nanocrystals

(Quantum Dots, Quantum Wires, andNanorods) 384

Acknowledgements 386References 386

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Chapter 14 Light Harvesting Strategies Inspired by Nature 389Evgeny Ostrumov, Chanelle Jumper and Gregory Scholes

14.1 Introduction 38914.2 Weakly-Coupled Chromophores: Forster Resonance

Energy Transfer Theory 391

14.3 Multi-Subunit Protein Complexes: Generalized

Forster Theory 394

14.4 Quantum Coherence in LH Proteins 39714.5 Strategies of Photoadaptation and Photoprotection 40014.6 Summary of the Strategies Adopted by Natural

Systems 401

Acknowledgements 402References 402

Chapter 15 Electronic Structure and Bonding of Water to Noble MetalSurfaces 406Hirohito Ogasawara and Anders Nilsson

15.1 Introduction 40615.2 H-up, H-down and Partially Dissociated Water

Layers 407

15.3 Competition Between Thermal Dissociation and

Desorption 411

15.4 Electronic Structure and Bonding Mechanism 41215.5 Conclusions 416Acknowledgements 416References 416

Chapter 16 New Perspectives and a Review of Progress 419Hans-Joachim Lewerenz and Laurence Peter

16.1 Introduction 41916.2 Advanced Photonics 419

16.2.1 Surface Plasmons 41916.2.2 Coupled Forster Excitation Energy Transfer 42416.2.3 Levy Processes 427

16.3 Electrodes Structural Aspects 43316.4 A Note on Electronic Properties of Transition

Metal Oxides 438

16.5 Looking Back 44316.5 Progress Towards Light Driven Water Splitting 444Acknowledgements 446References 446

Subject Index 450

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