List of Contributors ......................................... xvii
Preface ....................................................... xix
Editor Biography ............................................ xxiii
PART ONE—FUNDAMENTALS, MODELING, AND EXPERIMENTAL
INVESTIGATION OF PHOTOCATALYTIC REACTIONS FOR DIRECT SOLAR
HYDROGEN GENERATION
1 Solar Hydrogen Production by Photoelectrochemical
Water Splitting: The Promise and Challenge ................... 3
Eric L. Miller
1.1 Introduction ............................................ 3
1.2 Hydrogen or Hype? ....................................... 4
1.3 Solar Pathways to Hydrogen .............................. 5
1.3.1 The Solar Resource ............................... 5
1.3.2 Converting Sunlight .............................. 6
1.3.3 Solar-Thermal Conversion ......................... 7
1.3.4 Solar-Potential Conversion ....................... 8
1.3.5 Pathways to Hydrogen ............................. 9
1.4 Photoelectrochemical Water-Splitting ................... 10
1.4.1 Photoelectrochemistry ........................... 10
1.4.2 PEC Water-Splitting Reactions ................... 10
1.4.3 Solar-to-Hydrogen Conversion Efficiency ......... 13
1.4.4 Fundamental Process Steps ....................... 14
1.5 The Semiconductor/Electrolyte Interface ................ 14
1.5.1 Rectifying Junctions ............................ 14
1.5.2 A Solid-State Analogy: The np+ Junction ......... 15
1.5.3 PEC Junction Formation .......................... 17
1.5.4 Illuminated Characteristics ..................... 19
1.5.5 Fundamental Process Steps ....................... 20
1.6 Photoelectrode Implementations ......................... 23
1.6.1 Single-Junction Performance Limits .............. 23
1.6.2 Multijunction Performance Limits ................ 24
1.6.3 A Shining Example ............................... 27
1.7 The PEC Challenge ................................. 28
1.7.1 What's Needed, Really? .......................... 28
1.7.2 Tradeoffs and Compromises ....................... 29
1.7.3 The Race with PV-Electrolysis ................... 29
1.8 Facing the Challenge: Current PEC Materials Research ... 29
Acknowledgments ............................................. 32
References .................................................. 32
2 Modeling and Simulation of Photocatalytic Reactions at Ti02
Surfaces .................................................... 37
Hideyuki Kamisaka and Koichi Yamashita
2.1 Importance of Theoretical Studies on TiO2 Systems ...... 37
2.2 Doped TiO2 Systems: Carbon and Niobium Doping .......... 39
2.2.1 First-Principle Calculations on TiO2 ............ 39
2.2.2 C-Doped TiO2 .................................... 41
2.2.3 Nb-Doped TiO2 ................................... 45
2.3 Surface Hydroxyl Groups and the Photoinduced
Hydrophilicity of TiO2 ................................. 51
2.3.1 Speculated Active Species on TiO2 - Superoxide
Anion (O2-) and the Hydroxyl Radical (OH•) ...... 51
2.3.2 Theoretical Calculations of TiO2 Surfaces and
Adsorbents ...................................... 51
2.3.3 Surface Hydroxyl Groups and Photoinduced
Hydrophilic Conversion .......................... 53
2.4 Dye-Sensitized Solar Cells ............................. 58
2.4.1 Conventional Sensitizers: Ruthenium Compounds
and Organic Dyes ................................ 58
2.4.2 Multiexciton Generation in Quantum Dots:
A Novel Sensitizer for a DSSC ................... 59
2.4.3 Theoretical Estimation of the Decoherence Time
between the Electronic States in PbSe QDs ....... 60
2.5 Future Directions: Ab Initio Simulations and the
Local Excited States on TiO2 ........................... 63
2.5.1 Improvement of the DFT Functional ............... 64
2.5.2 Molecular Mechanics and Ab Initio Molecular
Dynamics ........................................ 65
2.5.3 Description of Local Excited States ............. 66
2.5.4 Nonadiabatic Behavior of a System and
Interfacial Electron Transfer ................... 67
Acknowledgments ............................................. 68
References .................................................. 68
3 Photocatalytic Reactions on Model Single Crystal Ti02
Surfaces .................................................... 77
G.I.N. Waterhouse and H. Idriss
3.1 TiO2 Single-Crystal Surfaces ........................... 78
3.2 Photoreactions Over Semiconductor Surfaces ............. 80
3.3 Ethanol Reactions Over TiO2 (l10) Surface .............. 81
3.4 Photocatalysis and Structure Sensitivity ............... 83
3.5 Hydrogen Production from Ethanol Over Au/TiO2
Catalysts .............................................. 84
3.6 Conclusions ............................................ 87
References .................................................. 87
4 Fundamental Reactions on Rutile Ti02(110) Model
Photocatalysts Studied by High-Resolution Scanning
Tunneling Microscopy ........................................ 91
Stefan Wendt, Ronnie T. Vang, and Flemming Besenbacher
4.1 Introduction ........................................... 91
4.2 Geometric Structure and Defects of the Rutile
TiO2 (110) Surface ..................................... 93
4.3 Reactions of Water with Oxygen Vacancies ............... 96
4.4 Splitting of Paired H Adatoms and Other Reactions
Observed on Partly Water Covered TiO2 ( 110) ........... 98
4.5 O2Dissociation and the Role of Ti Interstitials ........ 101
4.6 Intermediate Steps of the Reaction BetweenO2and
H Adatoms and the Role of Coadsorbed Water ............ 106
4.7 Bonding of Gold Nanoparticles on TiO2(l10) in
Different Oxidation States ............................ 112
4.8 Summary and Outlook ................................... 115
References ............................................ 117
PART TWO—ELECTRONIC STRUCTURE, ENERGETICS, AND TRANSPORT
DYNAMICS OF PHOTOCATALYST NANOSTRUCTURES
5 Electronic Structure Study of Nanostructured Transition
Metal Oxides Using Soft X-Ray Spectroscopy ................. 125
Jinghua Guo, Per-Anders Glans, Yi-Sheng Liu, and Chinglin
Chang
5.1 Introduction .......................................... 125
5.2 Soft X-Ray Spectroscopy ............................... 126
5.2.1 Soft X-Ray Absorption and Emission
Spectroscopy ................................... 126
5.2.2 Resonantly Excited Soft X-Ray Emission
Spectroscopy ................................... 127
5.3 Experiment Set-Up ..................................... 127
5.3.1 Beamline ....................................... 128
5.3.2 Spectrometer and Endstation .................... 129
5.3.3 Sample Arrangements ............................ 131
5.4 Results and Discussion ................................ 132
Acknowledgments ....................................... 139
References ............................................ 139
6 X-ray and Electron Spectroscopy Studies of Oxide
Semiconductors for Photoelectrochemical Hydrogen
Production ................................................. 143
Clemens Heske, Lothar Weinhardt, and Marcus Bär
6.1 Introduction .......................................... 143
6.2 Soft X-Ray and Electron Spectroscopies ................ 145
6.3 Electronic Surface-Level Positions of WO3 Thin
Films ................................................. 147
6.3.1 Introduction ................................... 147
6.3.2 Sample Handling and the Influence of X-Rays,
UV-Light and Low-Energy Electrons on the
Properties of the WO3 Surface .................. 147
6.3.3 Surface Band Edge Positions in Vacuum -
Determination with UPS/IPES .................... 149
6.3.4 Estimated Surface Band-Edge Positions in
Electrolyte .................................... 151
6.3.5 Conclusions .................................... 153
6.4 Soft X-Ray Spectroscopy of ZnO:Zn3N2 Thin Films ....... 154
6.4.1 Introduction ................................... 154
6.4.2 The О К XES Spectrum of ZnO:N Thin Films -
Determination of the Valence Band Maximum ...... 154
6.4.3 The Impact of Air Exposure on the Chemical
Structure of ZnO:N Thin Films .................. 155
6.4.4 Conclusions .................................... 157
6.5 In Situ Soft X-Ray Spectroscopy: A Brief Outlook ...... 158
6.6 Summary ............................................... 158
Acknowledgments ............................................ 159
References ................................................. 159
7 Applications of X-Ray Transient Absorption Spectroscopy
in Photocatalysis for Hydrogen Generation .................. 163
Lin X. Chen
7.1 Introduction .......................................... 163
7.2 X-Ray Transient Absorption Spectroscopy (XTA) ......... 165
7.3 Tracking Electronic and Nuclear Configurations in
Photoexcited Metalloporphyrins ........................ 171
7.4 Tracking Metal-Center Oxidation States in the MLCT
State of Metal Complexes .............................. 176
7.5 Tracking Transient Metal Oxidation States During
Hydrogen Generation ................................... 178
7.6 Prospects and Challenges in Future Studies ............ 180
Acknowledgments ............................................ 181
References ................................................. 181
8 Fourier-Transform Infrared and Raman Spectroscopy of Pure
and Doped Ti02 Photocatalysts .............................. 189
Lars Österlund
8.1 Introduction .......................................... 189
8.2 Vibrational Spectroscopy on TiO2 Photocatalysts:
Experimental Considerations ........................... 191
8.3 Raman Spectroscopy of Pure and Doped TiO2
Nanoparticles ......................................... 195
8.4 Gas-Solid Photocatalytic Reactions Probed by FTIR
Spectroscopy .......................................... 199
8.5 Model Gas-Solid Reactions on Pure and Doped TiO2
Nanoparticles Studied by FTIR Spectroscopy ............ 205
8.5.1 Reactions with Formic Acid ..................... 205
8.5.2 Reactions with Acetone ......................... 221
8.6 Summary and Concluding Remarks ........................ 229
Acknowledgments ............................................ 230
References ................................................. 230
9 Interfacial Electron Transfer Reactions in CdS Quantum
Dot Sensitized Ti02 Nanocrystalline Electrodes ............. 239
Yasuhiro Tachibana
9.1 Introduction .......................................... 239
9.2 Nanomaterials ......................................... 240
9.2.1 Semiconductor Quantum Dots ..................... 240
9.2.2 Metal Oxide Nanocrystalline Semiconductor
Films .......................................... 241
9.2.3 QD Sensitized Metal Oxide Semiconductor
Films .......................................... 242
9.3 Transient Absorption Spectroscopy ..................... 245
9.3.1 Principle ...................................... 245
9.3.2 Calculation of Absorption Difference ........... 245
9.3.3 System Arrangement ............................. 246
9.4 Controlling Interfacial Electron Transfer Reactions
by Nanomaterial Design ................................ 247
9.4.1 QD/Metal-Oxide Interface ....................... 248
9.4.2 QD/Electrolyte Interface ....................... 250
9.4.3 Conducting Glass/Electrolyte Interface ......... 252
9.5 Application of QD-Sensitized Metal-Oxide
Semiconductors to Solar Hydrogen Production ........... 258
9.6 Conclusion ............................................ 260
Acknowledgments ............................................ 260
References ................................................. 260
PART THREE—DEVELOPMENT OF ADVANCED NANOSTRUCTURES FOR
EFFICIENT SOLAR HYDROGEN PRODUCTION FROM CLASSICAL LARGE
BANDGAP SEMICONDUCTORS
10 Ordered Titanium Dioxide Nanotubular Arrays as
Photoanodes for Hydrogen Generation ........................ 267
M. Misra and K.S. Raja
10.1 Introduction ......................................... 267
10.2 Crystal Structure of TiO2 ............................. 268
10.2.1 Electronic and Defect Structure of TiO2 ........ 269
10.2.2 Preparation of TiO2 Nanotubes .................. 272
10.2.3 Energetics of Photodecomposition of Water on
TiO2 ........................................... 279
References ................................................. 288
11 Electrodeposition of Nanostructured ZnO Films and Their
Photoelectrochemical Properties ............................ 291
Torsten Oekermann
11.1 Introduction .......................................... 291
11.2 Fundamentals of Electrochemical Deposition ............ 292
11.3 Electrodeposition of Metal Oxides and Other
Compounds ............................................. 294
11.4 Electrodeposition of Zinc Oxide ....................... 295
11.4.1 Electrodeposition of Pure ZnO .................. 295
11.4.2 Electrodeposition of Doped ZnO ................. 297
11.4.3 P-n-Junctions Based on Electrodeposited ZnO .... 298
11.5 Electrodeposition of One- and Two-Dimensional ZnO
Nanostructures ........................................ 298
11.5.1 ZnO Nanorods ................................... 298
11.5.2 ZnO Nanotubes .................................. 301
11.5.3 Two-Dimensional ZnO Nanostructures ............. 302
11.6 Use of Additives in ZnO Electrodeposition ............. 303
11.6.1 Dye Molecules as Structure-Directing
Additives ...................................... 303
11.6.2 ZnO Electrodeposition with Surfactants ......... 307
11.6.3 Other Additives ................................ 311
11.7 Photoelectrochemical and Photovoltaic Properties ...... 312
11.7.1 Dye-Sensitized Solar Cells (DSSCs) ............. 312
11.7.2 Photoelectrochemical Investigation of the
Electron Transport in Porous ZnO Films ......... 316
11.7.3 Performance of Nanoporous Electrodeposited
ZnO Films in DSSCs ............................. 320
11.7.4 Use of ZnO Nanorods in Photovoltaics ........... 321
11.8 Photocatalytic Properties ........................ 322
11.9 Outlook ............................................... 323
References ................................................. 323
12 Nanostructured Thin-Film W03 Photoanodes for Solar Water
and Sea-Water Splitting .................................... 333
Bruce D. Alexander and Jan Augustynski
12.1 Historical Context .................................... 333
12.2 Macrocrystalline WO3 Films ............................ 334
12.3 Limitations of Macroscopic WO3 ........................ 336
12.4 Nanostructured Films .................................. 336
12.5 Tailoring WO3 Films Through a Modified Chimie Douce
Synthetic Route ....................................... 339
12.6 Surface Reactions at Nanocrystalline WO3 Electrodes ... 342
12.7 Conclusions and Outlook ............................... 345
References ................................................. 346
13 Nanostructured α-Fe203 in PEC Generation of Hydrogen ....... 349
Vibha R. Satsangi, Sahab Dass, and Rohit Shrivastav
13.1 Introduction .......................................... 349
13.2 α-Fe2O3 ............................................... 350
13.2.1 Structural and Electrical/Electronic
Properties ..................................... 350
13.2.2 α-Fe2O3 in PEC Splitting of Water .............. 351
13.3 Nanostructured α-Fe2O3 Photoelectrodes ................ 352
13.3.1 Preparation Techniques and
Photoelectrochemical Response .................. 353
13.3.2 Flatband Potential and Donor Density ........... 365
13.4 Strategies to Enhance Photoresponse ................... 368
13.4.1 Doping ......................................... 368
13.4.2 Choice of Electrolytes ......................... 373
13.4.3 Dye Sensitizers ................................ 374
13.4.4 Porosity ....................................... 375
13.4.5 Forward/Backward Illumination .................. 375
13.4.6 Loading of Metal/Metal Oxide ................... 377
13.4.7 Layered Structures ............................. 377
13.4.8 Deposition of Zn Islands ....................... 380
13.4.9 Swift Heavy Ion (SHI) Irradiation .............. 382
13.4.10 p/n Assemblies ................................ 385
13.5 Efficiency and Hydrogen Production .................... 386
13.6 Concluding Remarks .................................... 388
Acknowledgments ............................................ 393
References ................................................. 393
PART FOUR—NEW DESIGN AND APPROACHES TO BANDGAP PROFILING AND
VISIBLE-LIGHT-ACTIVE NANOSTRUCTURES
14 Photoelectrocatalyst Discovery Using High-Throughput
Methods and Combinatorial Chemistry ........................ 401
Alan Kleiman-Shwarsctein, Peng Zhang, Yongsheng Нu, and
Eric W. McFarland
14.1 Introduction .......................................... 401
14.2 The Use of High-Throughput and Combinatorial Methods
for the Discovery and Optimization of
Photoelectrocatalyst Material Systems ................. 402
14.2.1 The Use of High-Throughput and Combinatorial
Methods in Materials Science ................... 402
14.2.2 HTE Applications to PEC Discovery .............. 405
14.2.3 Absorbers ...................................... 408
14.2.4 Bulk Carrier Transport ......................... 411
14.2.5 Electrocatalysts ............................... 412
14.2.6 Morphology and Material System ................. 412
14.2.7 Library Format, Data Management and Analysis ... 414
14.3 Practical Methods of High-Throughput Synthesis of
Photoelectrocatalysts ................................. 415
14.3.1 Vapor Deposition ............................... 416
14.3.2 Liquid Phase Synthesis ......................... 417
14.3.3 Electrochemical Synthesis ...................... 419
14.3.4 Spray Pyrolysis ................................ 422
14.4 Photocatalyst Screening and Characterization .......... 423
14.4.1 High-Throughput Screening ...................... 424
14.4.2 Secondary Screening and Quantitative
Characterization ............................... 432
14.5 Specific Examples of High-Throughput Methodology
Applied to Photoelectrocatalysts ...................... 437
14.5.1 Solar Absorbers ................................ 437
14.5.2 Improving Charge-Transfer Efficiency ........... 443
14.5.3 Improved PEC Electrocatalysts .................. 448
14.5.4 Design and Assembly of a Complete
Nanostructured Photocatalytic Unit ............. 451
14.6 Summary and Outlook ................................... 453
References ................................................. 454
15 Multidimensional Nanostructures for Solar Water
Splitting: Synthesis, Properties, and Applications ......... 459
Abraham Wolcott and Jin Z. Zhang
15.1 Motivation for Developing Metal-Oxide
Nanostructures ........................................ 459
15.1.1 Introduction ................................... 459
15.1.2 PEC Water Splitting for Hydrogen Production .... 460
15.1.3 Metal-Oxide PEC Cells .......................... 460
15.1.4 Dye and QD Sensitization ....................... 462
15.1.5 Deposition Techniques for Metal Oxides ......... 462
15.2 Colloidal Methods for 0D Metal-Oxide Nanoparticle
Synthesis ............................................. 463
15.2.1 Colloidal Nanoparticles ........................ 463
15.2.2 TiO2 Sol-Gel Synthesis ......................... 464
15.2.3 TiO2 Hydrothermal Synthesis .................... 465
15.2.4 TiO2 Solvothermal and Sonochemical Synthesis ... 466
15.2.5 TiO2 Template-Driven Synthesis ................. 468
15.2.6 Sol-Gel WO3 Colloidal Synthesis ................ 470
15.2.7 WO3 Hydrothermal Synthesis ..................... 470
15.2.8 WO3 Solvothermal and Sonochemical Synthesis .... 470
15.2.9 WO3 Template Driven Synthesis .................. 471
15.2.10 ZnO Sol-Gel Nanoparticle Synthesis ............ 473
15.2.11 ZnO Hydrothermal Synthesis .................... 474
15.2.12 ZnO Solvothermal and Sonochemical Synthesis ... 475
15.2.13 ZnO Template-Driven Synthesis ................. 479
15.3 ID Metal-Oxide Nanostructures ......................... 481
15.3.1 Colloidal Synthesis and Fabrication ............ 481
15.3.2 Synthesis and Fabrication of ID TiO2
Nanostructures ................................. 481
15.3.3 Colloidal Synthesis and Fabrication of ID WO3
Nanostructures ................................. 486
15.3.4 Colloidal Synthesis and Fabrication of ID ZnO
Nanostructures ................................. 487
15.4 2D Metal-Oxide Nanostructures ......................... 488
15.4.1 Colloidal Synthesis of 2D TiO2
Nanostructures ................................. 488
15.4.2 Colloidal Synthesis of 2D WO3 Nanostructures ... 490
15.4.3 Colloidal Synthesis of 2D ZnO Nanostructures ... 491
15.5 Conclusion ............................................ 492
Acknowledgments ............................................ 493
References ................................................. 493
16 Nanoparticle-Assembled Catalysts for Photochemical
Water Splitting ............................................ 507
Frank E. Osterloh
16.1 Introduction .......................................... 507
16.2 Two-Component Catalysts ............................... 509
16.2.1 Synthetic and Structural Aspects ............... 509
16.2.2 Photocatalytic Hydrogen Evolution .............. 511
16.2.3 Peroxide Formation ............................. 513
16.2.4 Water Electrolysis ............................. 515
16.3 CdSe Nanoribbons as a Quantum-Confined Water-
Splitting Catalyst .................................... 516
16.4 Conclusion and Outlook ................................ 518
Acknowledgment ............................................. 519
References ................................................. 519
17 Quantum-Confined Visible-Light-Active Metal-Oxide
Nanostructures for Direct Solar-to-Hydrogen Generation ..... 523
Lionel Vayssieres
17.1 Introduction .......................................... 523
17.2 Design of Advanced Semiconductor Nanostructures
by Cost-Effective Technique ........................... 524
17.2.1 Concepts and Experimental Set-Up of Aqueous
Chemical Growth ................................ 524
17.2.2 Achievements in Aqueous Design of Highly
Oriented Metal-Oxide Arrays .................... 528
17.3 Quantum Confinement Effects for Photovoltaics and
Solar Hydrogen Generation ............................. 529
17.3.1 Multiple Exciton Generation .................... 530
17.3.2 Quantum-Well Structures ........................ 531
17.3.3 Intermediate Band Materials .................... 531
17.4 Novel Cost-Effective Visible-Light-Active (Hetero)
Nanostructures for Solar Hydrogen Generation .......... 533
17.4.1 Iron-Oxide Quantum-Rod Arrays .................. 533
17.4.2 Doped Iron-Oxide Quantum-Rod Arrays ............ 541
17.4.3 Quantum-Dot-Quantum-Rod Iron-Oxide
Heteronanostructure Arrays .................... 545
17.4.4 Iron Oxide Oriented Porous Nanostructures ...... 546
17.5 Conclusion and Perspectives ........................... 548
References ................................................. 548
18 Effects of Metal-Ion Doping, Removal and Exchange on
Photocatalytic Activity of Metal Oxides and Nitrides for
Overall Water Splitting .................................... 559
Yasunobu Inoue
18.1 Introduction .......................................... 559
18.2 Experimental Procedures ............................... 561
18.3 Effects of Metal Ion Doping ........................... 561
18.3.1 Sr2+ Ion-Doped CeO2 ............................. 561
18.3.2 Metal-Ion Doped GaN ............................ 564
18.4 Effects of Metal-Ion Removal .......................... 569
18.5 Effects of Metal-Ion Exchange on Photocatalysis ....... 573
18.5.1 Yxn2-xO3 ........................................ 573
18.5.2 Scxln2-x03 ...................................... 580
18.5.3 YxIn2-xGe2O7 .................................... 582
18.6 Effects of Zn Addition to Indate and Stannate ......... 583
18.6.1 Li1.6Zn1.6Sn2.8O8 ................................ 584
18.6.2 Ba3Zn5In2O11 .................................... 584
18.7 Conclusions ........................................... 585
Acknowledgments ............................................ 586
References ................................................. 586
19 Supramolecular Complexes as Photoinitiated Electron
Collectors: Applications in Solar Hydrogen Production ...... 589
Shamindri M. Arachchige and Karen J. Brewer
19.1 Introduction .......................................... 589
19.1.1 Solar Water Splitting .......................... 589
19.1.2 Supramolecular Complexes and Photochemical
Molecular Devices .............................. 590
19.1.3 Polyazine Light Absorbers ...................... 591
19.1.4 Polyazine Bridging Ligands to Construct
Photochemical Molecular Devices ................ 594
19.1.5 Multi-Component System for Visible Light
Reduction of Water ............................. 595
19.1.6 Photoinitiated Charge Separation ............... 596
19.2 Supramolecular Complexes for Photoinitiated Electron
Collection ............................................ 598
19.2.1 Photoinitiated Electron Collection on
a Bridging Ligand .............................. 598
19.2.2 Ruthenium Polyazine Light Absorbers Coupled
Through an Aromatic Bridging Ligand ............ 600
19.2.3 Photoinitiated Electron Collection on
a Platinum Metal ............................... 602
19.2.4 Two-Electron Mixed-Valence Complexes for
Multielectron Photochemistry ................... 604
19.2.5 Rhodium-Centered Electron Collectors ........... 605
19.2.6 Mixed-Metal Systems for Solar Hydrogen
Production ..................................... 613
19.3 Conclusions ........................................... 614
List of Abbreviations ...................................... 616
Acknowledgments ............................................ 616
References ................................................. 617
PART FIVE—NEW DEVICES FOR SOLAR THERMAL HYDROGEN GENERATION
20 Novel Monolithic Reactors for Solar Thermochemical Water
Splitting .................................................. 623
Athanasios G. Konstandopoulos and Souzana Lorentzou
20.1 Introduction .......................................... 623
20.1.1 Energy Production and Nanotechnology ........... 623
20.1.2 Application of Solar Technologies .............. 624
20.2 Solar Hydrogen Production ............................. 624
20.2.1 Solar Hydrogen Production: Thermochemical
Processes ...................................... 625
20.2.2 Solar Chemical Reactors ........................ 626
20.3 HYDROSOL Reactor ...................................... 627
20.3.1 The Idea ....................................... 627
20.3.2 Redox Materials ................................ 627
20.3.3 Water Splitting: Laboratory Tests .............. 629
20.3.4 HYDROSOL Reactors .............................. 630
20.3.5 Solar Testing .................................. 631
20.3.6 Simulation ..................................... 633
20.3.7 Future Developments ............................ 636
20.4 HYDROSOL Process ...................................... 636
20.5 Conclusions ........................................... 637
Acknowledgments ............................................ 638
References ................................................. 638
21 Solar Thermal and Efficient Solar Thermal/Electrochemical
Photo Hydrogen Generation .................................. 641
Stuart Licht
21.1 Comparison of Solar Hydrogen Processes ................ 641
21.2 STEP (Solar Thermal Electrochemical Photo)
Generation of H2 ...................................... 646
21.3 STEP Theory ........................................... 648
21.4 STEP Experiment: Efficient Solar Water Splitting ...... 653
21.5 NonHybrid Solar Thermal Processes ..................... 657
21.5.1 Direct Solar Thermal Hydrogen Generation ....... 657
21.5.2 Indirect (Multistep) Solar Thermal H2
Generation ..................................... 659
21.6 Conclusions ........................................... 660
References ................................................. 661
Index ......................................................... 665
Index ......................................................... 665
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