On Solar Hydrogen and Nanotechnology

Lionel Vayssieres is a senior researcher at theInternationalCenter for Young Scientists, National Institute for Materials Science (NIMS) inTsukuba,Japan; a R&D consultant; and a guest scientist at the Chemical Sciences Division and Advanced Light Source at Lawrence Berkeley National Laboratory,USA. He obtained his M.Sc. in Physical Chemistry (1991) and Ph.D. in Inorganic Chemistry (1995) from the Université Pierre et Marie Curie inParis. He then carried out postdoctoral research at Uppsala University, Sweden and also spent time as a visiting researcher at the University of Texas at Austin, the UNESCO Centre for Macromolecules & Materials, Stellenbosch University, the Glenn T. Seaborg Center at Lawrence Berkeley National Laboratory, the Texas Materials Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), the University of Queensland, Nanyang Technological University, and the iThemba LABS in South Africa.Vayssieres has (co-)authored around 50 refereed publications, which have generated over 1600 citations (since 2000). He has presented over 160 lectures in over 25 countries and has acted as chairman, executive program committee member, and advisory member at major international conferences and projects worldwide. Vayssieres is the founder and editor-in-chief of the International Journal of Nanotechnology and founder, organizer and chairman of the first international symposium dedicated to Solar Hydrogen & Nanotechnology (San Diego, CA 2006), which was sponsored by the International Society for Optical Engineering. He has been working on nanomaterials for solar energy conversion since 1996 and published the first nanorod-based solar cells paper in 2000.

• List of Contributors xviiPreface xixEditor Biography xxiiiPart One—fundamentals, Modeling, and Experimental Investigation of Photocatalytic Reactions for Direct Solar Hydrogen Generation1 Solar Hydrogen Production by Photoelectrochemical Water Splitting: The Promise and Challenge 3Eric L. Miller1.1 Introduction 31.2 Hydrogen or Hype? 41.3 Solar Pathways to Hydrogen 51.3.1 The Solar Resource 51.3.2 Converting Sunlight 61.3.3 Solar-Thermal Conversion 71.3.4 Solar-Potential Conversion 81.3.5 Pathways to Hydrogen 91.4 Photoelectrochemical Water-Splitting 101.4.1 Photoelectrochemistry 101.4.2 PEC Water-Splitting Reactions 101.4.3 Solar-to-Hydrogen Conversion Efficiency 131.4.4 Fundamental Process Steps 141.5 The Semiconductor/Electrolyte Interface 141.5.1 Rectifying Junctions 141.5.2 A Solid-State Analogy: The np þ Junction 151.5.3 PEC Junction Formation 171.5.4 Illuminated Characteristics 191.5.5 Fundamental Process Steps 201.6 Photoelectrode Implementations 231.6.1 Single-Junction Performance Limits 231.6.2 Multijunction Performance Limits 241.6.3 A Shining Example 271.7 The PEC Challenge 281.7.1 What’s Needed, Really? 281.7.2 Tradeoffs and Compromises 291.7.3 The Race with PV-Electrolysis 291.8 Facing the Challenge: Current PEC Materials Research 29Acknowledgments 32References 322 Modeling and Simulation of Photocatalytic Reactions at TiO 2 Surfaces 37Hideyuki Kamisaka and Koichi Yamashita2.1 Importance of Theoretical Studies on TiO 2 Systems 372.2 Doped TiO 2 Systems: Carbon and Niobium Doping 392.2.1 First-Principle Calculations on TiO 2 392.2.2 C-Doped TiO 2 412.2.3 Nb-Doped TiO 2 452.3 Surface Hydroxyl Groups and the Photoinduced Hydrophilicity of TiO 2 512.3.1 Speculated Active Species on TiO 2 – Superoxide Anion (O 2) and the Hydroxyl Radical (OH) 512.3.2 Theoretical Calculations of TiO 2 Surfaces and Adsorbents 512.3.3 Surface Hydroxyl Groups and Photoinduced Hydrophilic Conversion 532.4 Dye-Sensitized Solar Cells 582.4.1 Conventional Sensitizers: Ruthenium Compounds and Organic Dyes 582.4.2 Multiexciton Generation in Quantum Dots: A Novel Sensitizer for a DSSC 592.4.3 Theoretical Estimation of the Decoherence Time between the Electronic States in PbSe QDs 602.5 Future Directions: Ab Initio Simulations and the Local Excited States on TiO 2 632.5.1 Improvement of the DFT Functional 642.5.2 Molecular Mechanics and Ab Initio Molecular Dynamics 652.5.3 Description of Local Excited States 662.5.4 Nonadiabatic Behavior of a System and Interfacial Electron Transfer 67Acknowledgments 68References 683 Photocatalytic Reactions on Model Single Crystal TiO 2 Surfaces 77G.I.N. Waterhouse and H. Idriss3.1 TiO 2 Single-Crystal Surfaces 783.2 Photoreactions Over Semiconductor Surfaces 803.3 Ethanol Reactions Over TiO 2 (110) Surface 813.4 Photocatalysis and Structure Sensitivity 833.5 Hydrogen Production from Ethanol Over Au/TiO 2 Catalysts 843.6 Conclusions 87References 874 Fundamental Reactions on Rutile TiO 2 (110) Model Photocatalysts Studied by High-Resolution Scanning Tunneling Microscopy 91Stefan Wendt, Ronnie T. Vang, and Flemming Besenbacher4.1 Introduction 914.2 Geometric Structure and Defects of the Rutile TiO 2 (110) Surface 934.3 Reactions of Water with Oxygen Vacancies 964.4 Splitting of Paired H Adatoms and Other Reactions Observed on Partly Water Covered TiO 2 (110) 984.5 O 2 Dissociation and the Role of Ti Interstitials 1014.6 Intermediate Steps of the Reaction Between O 2 and H Adatoms and the Role of Coadsorbed Water 1064.7 Bonding of Gold Nanoparticles on TiO 2 (110) in Different Oxidation States 1124.8 Summary and Outlook 115References 117Part Two—electronic Structure, Energetics, And Transport Dynamics of Photocatalyst Nanostructures5 Electronic Structure Study of Nanostructured Transition Metal Oxides Using Soft X-Ray Spectroscopy 125Jinghua Guo, Per-Anders Glans, Yi-Sheng Liu, and Chinglin Chang5.1 Introduction 1255.2 Soft X-Ray Spectroscopy 1265.2.1 Soft X-Ray Absorption and Emission Spectroscopy 1265.2.2 Resonantly Excited Soft X-Ray Emission Spectroscopy 1275.3 Experiment Set-Up 1275.3.1 Beamline 1285.3.2 Spectrometer and Endstation 1295.3.3 Sample Arrangements 1315.4 Results and Discussion 132Acknowledgments 139References 1396 X-ray and Electron Spectroscopy Studies of Oxide Semiconductors for Photoelectrochemical Hydrogen Production 143Clemens Heske, Lothar Weinhardt, and Marcus B€ar6.1 Introduction 1436.2 Soft X-Ray and Electron Spectroscopies 1456.3 Electronic Surface-Level Positions of WO 3 Thin Films 1476.3.1 Introduction 1476.3.2 Sample Handling and the Influence of X-Rays, UV-Light and Low-Energy Electrons on the Properties of the WO 3 Surface 1476.3.3 Surface Band Edge Positions in Vacuum – Determination with UPS/IPES 1496.3.4 Estimated Surface Band-Edge Positions in Electrolyte 1516.3.5 Conclusions 1536.4 Soft X-Ray Spectroscopy of ZnO:Zn 3 N 2 Thin Films 1546.4.1 Introduction 1546.4.2 The O K XES Spectrum of ZnO:N Thin Films – Determination of the Valence Band Maximum 1546.4.3 The Impact of Air Exposure on the Chemical Structure of ZnO:N Thin Films 1556.4.4 Conclusions 1576.5 In Situ Soft X-Ray Spectroscopy: A Brief Outlook 1586.6 Summary 158Acknowledgments 159References 1597 Applications of X-Ray Transient Absorption Spectroscopy in Photocatalysis for Hydrogen Generation 163Lin X. Chen7.1 Introduction 1637.2 X-Ray Transient Absorption Spectroscopy (XTA) 1657.3 Tracking Electronic and Nuclear Configurations in Photoexcited Metalloporphyrins 1717.4 Tracking Metal-Center Oxidation States in the MLCT State of Metal Complexes 1767.5 Tracking Transient Metal Oxidation States During Hydrogen Generation 1787.6 Prospects and Challenges in Future Studies 180Acknowledgments 181References 1818 Fourier-Transform Infrared and Raman Spectroscopy of Pure and Doped TiO 2 Photocatalysts 189Lars Österlund8.1 Introduction 1898.2 Vibrational Spectroscopy on TiO 2 Photocatalysts: Experimental Considerations 1918.3 Raman Spectroscopy of Pure and Doped TiO 2 Nanoparticles 1958.4 Gas–Solid Photocatalytic Reactions Probed by FTIR Spectroscopy 1998.5 Model Gas–Solid Reactions on Pure and Doped TiO 2 Nanoparticles Studied by FTIR Spectroscopy 2058.5.1 Reactions with Formic Acid 2058.5.2 Reactions with Acetone 2218.6 Summary and Concluding Remarks 229Acknowledgments 230References 2309 Interfacial Electron Transfer Reactions in CdS Quantum Dot Sensitized TiO 2 Nanocrystalline Electrodes 239Yasuhiro Tachibana9.1 Introduction 2399.2 Nanomaterials 2409.2.1 Semiconductor Quantum Dots 2409.2.2 Metal Oxide Nanocrystalline Semiconductor Films 2419.2.3 QD Sensitized Metal Oxide Semiconductor Films 2429.3 Transient Absorption Spectroscopy 2459.3.1 Principle 2459.3.2 Calculation of Absorption Difference 2459.3.3 System Arrangement 2469.4 Controlling Interfacial Electron Transfer Reactions by Nanomaterial Design 2479.4.1 QD/Metal-Oxide Interface 2489.4.2 QD/Electrolyte Interface 2509.4.3 Conducting Glass/Electrolyte Interface 2529.5 Application of QD-Sensitized Metal-Oxide Semiconductors to Solar Hydrogen Production 2589.6 Conclusion 260Acknowledgments 260References 260Part Three—development of Advanced Nanostructures For Efficient Solar Hydrogen Production From Classical Large Bandgap Semiconductors10 Ordered Titanium Dioxide Nanotubular Arrays as Photoanodes for Hydrogen Generation 267M. Misra and K.S. Raja10.1 Introduction 26710.2 Crystal Structure of TiO 2 26810.2.1 Electronic and Defect Structure of TiO 2 26910.2.2 Preparation of TiO 2 Nanotubes 27210.2.3 Energetics of Photodecomposition of Water on TiO 2 279References 28811 Electrodeposition of Nanostructured ZnO Films and Their Photoelectrochemical Properties 291Torsten Oekermann11.1 Introduction 29111.2 Fundamentals of Electrochemical Deposition 29211.3 Electrodeposition of Metal Oxides and Other Compounds 29411.4 Electrodeposition of Zinc Oxide 29511.4.1 Electrodeposition of Pure ZnO 29511.4.2 Electrodeposition of Doped ZnO 29711.4.3 P-n-Junctions Based on Electrodeposited ZnO 29811.5 Electrodeposition of One- and Two-Dimensional ZnO Nanostructures 29811.5.1 ZnO Nanorods 29811.5.2 ZnO Nanotubes 30111.5.3 Two-Dimensional ZnO Nanostructures 30211.6 Use of Additives in ZnO Electrodeposition 30311.6.1 Dye Molecules as Structure-Directing Additives 30311.6.2 ZnO Electrodeposition with Surfactants 30711.6.3 Other Additives 31111.7 Photoelectrochemical and Photovoltaic Properties 31211.7.1 Dye-Sensitized Solar Cells (DSSCs) 31211.7.2 Photoelectrochemical Investigation of the Electron Transport in Porous ZnO Films 31611.7.3 Performance of Nanoporous Electrodeposited ZnO Films in DSSCs 32011.7.4 Use of ZnO Nanorods in Photovoltaics 32111.8 Photocatalytic Properties 32211.9 Outlook 323References 32312 Nanostructured Thin-Film WO 3 Photoanodes for Solar Water and Sea-Water Splitting 333Bruce D. Alexander and Jan Augustynski12.1 Historical Context 33312.2 Macrocrystalline WO 3 Films 33412.3 Limitations of Macroscopic WO 3 33612.4 Nanostructured Films 33612.5 Tailoring WO 3 Films Through a Modified Chimie Douce Synthetic Route 33912.6 Surface Reactions at Nanocrystalline WO 3 Electrodes 34212.7 Conclusions and Outlook 345References 34613 Nanostructured a-Fe 2 O 3 in PEC Generation of Hydrogen 349Vibha R. Satsangi, Sahab Dass, and Rohit Shrivastav13.1 Introduction 34913.2 a-Fe 2 O 3 35013.2.1 Structural and Electrical/Electronic Properties 35013.2.2 a-Fe 2 O 3 in PEC Splitting of Water 35113.3 Nanostructured a-Fe 2 O 3 Photoelectrodes 35213.3.1 Preparation Techniques and Photoelectrochemical Response 35313.3.2 Flatband Potential and Donor Density 36513.4 Strategies to Enhance Photoresponse 36813.4.1 Doping 36813.4.2 Choice of Electrolytes 37313.4.3 Dye Sensitizers 37413.4.4 Porosity 37513.4.5 Forward/Backward Illumination 37513.4.6 Loading of Metal/Metal Oxide 37713.4.7 Layered Structures 37713.4.8 Deposition of Zn Islands 38013.4.9 Swift Heavy Ion (SHI) Irradiation 38213.4.10 p/n Assemblies 38513.5 Efficiency and Hydrogen Production 38613.6 Concluding Remarks 388Acknowledgments 393References 393Part Four—new Design and Approaches to Bandgap Profiling and Visible-light-active Nanostructures14 Photoelectrocatalyst Discovery Using High-Throughput Methods and Combinatorial Chemistry 401Alan Kleiman-Shwarsctein, Peng Zhang, Yongsheng Hu, and Eric W. McFarland14.1 Introduction 40114.2 The Use of High-Throughput and Combinatorial Methods for the Discovery and Optimization of Photoelectrocatalyst Material Systems 40214.2.1 The Use of High-Throughput and Combinatorial Methods in Materials Science 40214.2.2 HTE Applications to PEC Discovery 40514.2.3 Absorbers 40814.2.4 Bulk Carrier Transport 41114.2.5 Electrocatalysts 41214.2.6 Morphology and Material System 41214.2.7 Library Format, Data Management and Analysis 41414.3 Practical Methods of High-Throughput Synthesis of Photoelectrocatalysts 41514.3.1 Vapor Deposition 41614.3.2 Liquid Phase Synthesis 41714.3.3 Electrochemical Synthesis 41914.3.4 Spray Pyrolysis 42214.4 Photocatalyst Screening and Characterization 42314.4.1 High-Throughput Screening 42414.4.2 Secondary Screening and Quantitative Characterization 43214.5 Specific Examples of High-Throughput Methodology Applied to Photoelectrocatalysts 43714.5.1 Solar Absorbers 43714.5.2 Improving Charge-Transfer Efficiency 44314.5.3 Improved PEC Electrocatalysts 44814.5.4 Design and Assembly of a Complete Nanostructured Photocatalytic Unit 45114.6 Summary and Outlook 453References 45415 Multidimensional Nanostructures for Solar Water Splitting: Synthesis, Properties, and Applications 459Abraham Wolcott and Jin Z. Zhang15.1 Motivation for Developing Metal-Oxide Nanostructures 45915.1.1 Introduction 45915.1.2 PEC Water Splitting for Hydrogen Production 46015.1.3 Metal-Oxide PEC Cells 46015.1.4 Dye and QD Sensitization 46215.1.5 Deposition Techniques for Metal Oxides 46215.2 Colloidal Methods for 0D Metal-Oxide Nanoparticle Synthesis 46315.2.1 Colloidal Nanoparticles 46315.2.2 TiO 2 Sol-Gel Synthesis 46415.2.3 TiO 2 Hydrothermal Synthesis 46515.2.4 TiO 2 Solvothermal and Sonochemical Synthesis 46615.2.5 TiO 2 Template-Driven Synthesis 46815.2.6 Sol-Gel WO 3 Colloidal Synthesis 47015.2.7 WO 3 Hydrothermal Synthesis 47015.2.8 WO 3 Solvothermal and Sonochemical Synthesis 47015.2.9 WO 3 Template Driven Synthesis 47115.2.10 ZnO Sol-Gel Nanoparticle Synthesis 47315.2.11 ZnO Hydrothermal Synthesis 47415.2.12 ZnO Solvothermal and Sonochemical Synthesis 47515.2.13 ZnO Template-Driven Synthesis 47915.3 1D Metal-Oxide Nanostructures 48115.3.1 Colloidal Synthesis and Fabrication 48115.3.2 Synthesis and Fabrication of 1D TiO 2 Nanostructures 48115.3.3 Colloidal Synthesis and Fabrication of 1D WO 3 Nanostructures 48615.3.4 Colloidal Synthesis and Fabrication of 1D ZnO Nanostructures 48715.4 2D Metal-Oxide Nanostructures 48815.4.1 Colloidal Synthesis of 2D TiO 2 Nanostructures 48815.4.2 Colloidal Synthesis of 2D WO 3 Nanostructures 49015.4.3 Colloidal Synthesis of 2D ZnO Nanostructures 49115.5 Conclusion 492Acknowledgments 493References 49316 Nanoparticle-Assembled Catalysts for Photochemical Water Splitting 507Frank E. Osterloh16.1 Introduction 50716.2 Two-Component Catalysts 50916.2.1 Synthetic and Structural Aspects 50916.2.2 Photocatalytic Hydrogen Evolution 51116.2.3 Peroxide Formation 51316.2.4 Water Electrolysis 51516.3 CdSe Nanoribbons as a Quantum-Confined Water-Splitting Catalyst 51616.4 Conclusion and Outlook 518Acknowledgment 519References 51917 Quantum-Confined Visible-Light-Active Metal-Oxide Nanostructures for Direct Solar-to-Hydrogen Generation 523Lionel Vayssieres17.1 Introduction 52317.2 Design of Advanced Semiconductor Nanostructures by Cost-Effective Technique 52417.2.1 Concepts and Experimental Set-Up of Aqueous Chemical Growth 52417.2.2 Achievements in Aqueous Design of Highly Oriented Metal-Oxide Arrays 52817.3 Quantum Confinement Effects for Photovoltaics and Solar Hydrogen Generation 52917.3.1 Multiple Exciton Generation 53017.3.2 Quantum-Well Structures 53117.3.3 Intermediate Band Materials 53117.4 Novel Cost-Effective Visible-Light-Active (Hetero)Nanostructures for Solar Hydrogen Generation 53317.4.1 Iron-Oxide Quantum-Rod Arrays 53317.4.2 Doped Iron-Oxide Quantum-Rod Arrays 54117.4.3 Quantum-Dot–Quantum-Rod Iron-Oxide Heteronanostructure Arrays 54517.4.4 Iron Oxide Oriented Porous Nanostructures 54617.5 Conclusion and Perspectives 548References 54818 Effects of Metal-Ion Doping, Removal and Exchange on Photocatalytic Activity of Metal Oxides and Nitrides for Overall Water Splitting 559Yasunobu Inoue18.1 Introduction 55918.2 Experimental Procedures 56118.3 Effects of Metal Ion Doping 56118.3.1 Sr 2 þ Ion-Doped CeO 2 56118.3.2 Metal-Ion Doped GaN 56418.4 Effects of Metal-Ion Removal 56918.5 Effects of Metal-Ion Exchange on Photocatalysis 57318.5.1 Y X in 2 X O 3 57318.5.2 Sc X in 2 X O 3 58018.5.3 Y X in 2 X Ge 2 O 7 58218.6 Effects of Zn Addition to Indate and Stannate 58318.6.1 li 1.6 Zn 1.6 Sn 2.8 O 8 58418.6.2 Ba 3 Zn 5 In 2 O 11 58418.7 Conclusions 585Acknowledgments 586References 58619 Supramolecular Complexes as Photoinitiated Electron Collectors: Applications in Solar Hydrogen Production 589Shamindri M. Arachchige and Karen J. Brewer19.1 Introduction 58919.1.1 Solar Water Splitting 58919.1.2 Supramolecular Complexes and Photochemical Molecular Devices 59019.1.3 Polyazine Light Absorbers 59119.1.4 Polyazine Bridging Ligands to Construct Photochemical Molecular Devices 59419.1.5 Multi-Component System for Visible Light Reduction of Water 59519.1.6 Photoinitiated Charge Separation 59619.2 Supramolecular Complexes for Photoinitiated Electron Collection 59819.2.1 Photoinitiated Electron Collection on a Bridging Ligand 59819.2.2 Ruthenium Polyazine Light Absorbers Coupled Through an Aromatic Bridging Ligand 60019.2.3 Photoinitiated Electron Collection on a Platinum Metal 60219.2.4 Two-Electron Mixed-Valence Complexes for Multielectron Photochemistry 60419.2.5 Rhodium-Centered Electron Collectors 60519.2.6 Mixed-Metal Systems for Solar Hydrogen Production 61319.3 Conclusions 614List of Abbreviations 616Acknowledgments 616References 617Part Five—new Devices for Solar Thermal Hydrogen Generation20 Novel Monolithic Reactors for Solar Thermochemical Water Splitting 623Athanasios G. Konstandopoulos and Souzana Lorentzou20.1 Introduction 62320.1.1 Energy Production and Nanotechnology 62320.1.2 Application of Solar Technologies 62420.2 Solar Hydrogen Production 62420.2.1 Solar Hydrogen Production: Thermochemical Processes 62520.2.2 Solar Chemical Reactors 62620.3 HYDROSOL Reactor 62720.3.1 The Idea 62720.3.2 Redox Materials 62720.3.3 Water Splitting: Laboratory Tests 62920.3.4 HYDROSOL Reactors 63020.3.5 Solar Testing 63120.3.6 Simulation 63320.3.7 Future Developments 63620.4 HYDROSOL Process 63620.5 Conclusions 637Acknowledgments 638References 63821 Solar Thermal and Efficient Solar Thermal/Electrochemical Photo Hydrogen Generation 641Stuart Licht21.1 Comparison of Solar Hydrogen Processes 64121.2 STEP (Solar Thermal Electrochemical Photo) Generation of H 2 64621.3 STEP Theory 64821.4 STEP Experiment: Efficient Solar Water Splitting 65321.5 NonHybrid Solar Thermal Processes 65721.5.1 Direct Solar Thermal Hydrogen Generation 65721.5.2 Indirect (Multistep) Solar Thermal H 2 Generation 65921.6 Conclusions 660References 661Index 665

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