Energy Resources through Photochemistry and Catalysis

Energy Resources through Photochemistry and Catalysis reviews the state of the art in the development of energy conversion devices based on catalytic and photochemical reactions. The focus is on catalysis of redox reactions and their application to the photocleavage of water, reduction of carbon dioxide, and fixation of nitrogen. Some fundamental aspects of catalysis as it relates to processes of light energy harvesting and charge separation in photochemical or photoelectrochemical conversion systems are also discussed. This monograph is comprised of 16 chapters covering light-induced redox reactions and reaction dynamics in organized assemblies such as micelles, colloidal metals, or semiconductors, together with strategies for molecular engineering of artificial photosynthetic devices. The principles of electrochemical conversion of light energy via semiconductor electrodes or semiconducting particles are also considered. Furthermore, thermodynamic characteristics for some reactions that can be utilized for storage of solar energy in the form of chemical energy are examined. The remaining chapters look at the role of porphyrins in natural and artificial photosynthesis; the use of semiconductor powders and particulate systems for photocatalysis and photosynthesis; and hydrogen-generating solar cells based on platinum-group metal activated photocathodes. This text will be a useful resource for scientists and policymakers concerned with finding alternative sources of energy.

Contributors

Preface

1. Light-Induced and Thermal Electron-Transfer Reactions

I. Introduction

II. Kinetic Formulation

III. Classical Approach to Electron-Transfer Reactions

IV. Quantum Mechanical Approach to Electron-Transfer Reactions

V. Comparison between the Classical and Quantum Mechanical Models

VI. Peculiar Features of Electronically Excited States as Reactants in Electron-Transfer Processes

VII. Correlations of Rate Constants

VIII. Discussion of Selected Experimental Results

IX. Conclusion

References

2. Dynamics of Light-Induced Energy and Electron Transfer in Organized Assemblies

I. Introduction

II. General Consideration of Organized Structure

III. Kinetic Processes in Micellar Media

IV. Kinetics in Other Organized Assemblies

V. Conclusion

References

3. Molecular Engineering in Photo-conversion Systems

I. Introduction

II. Self-Organization and Light-Induced Charge Separation in Solutions of Amphiphilic Redox Chromophores

III. Water-Cleavage Cycles and Development of Artificial Analogs of Photosystem II of Green Plants

IV. Colloidal Semiconductors

V. Conclusions

References

4. Photocatalytic Water Reduction to H2: Principles of Redox Catalysis by Colloidal-Metal "Microelectrodes"

I. Introduction

II. The Electrochemical Model

III. A Simple Electrochemical Theory

IV. Quantitative Aspects

V. Preparation and Characterization of Active Metal Colloids

VI. Assays of Activity for H20 Reduction

VII. Experimental Results

VIII. Related Systems

Appendix: Equations for Current-Potential Curves as Applied to Heterogeneous Catalysis

References

5. Development of Molecular Photocatalytic Systems for Solar-Energy Conversion: Catalysts for Oxygen and Hydrogen Evolution from Water

I. Introduction

II. Hydrogen Evolution from Water

III. Oxygen Evolution from Water

IV. Photochemical Charge Separation

References

6. The Role of Porphyrins in Natural and Artificial Photosynthesis

I. Introduction

II. Photosynthesis

III. Light Harvesting

IV. Charge Separation

V. Charge Transport

VI. Oxygen Formation

VII. Fuel Production

VIII. Conclusions

References

7. Semiconductor Particulate Systems for Photocatalysis and Photosynthesis: An Overview

I. Introduction

II. Photoprocesses with "Naked" Semiconductor Powder Dispersions

III. Photoprocesses with "Metalized" Semiconductor Powder Dispersions

IV. Photoprocesses in Semiconductor Dispersions Loaded with Oxides: Hole Transfer and Bi-functional Catalysis

V. Semiconductor Dispersions as "Carriers" of Catalysts and Photosensitizers

VI. Physical Methods in the Study of Semiconductor Dispersions and Colloids

VII. Addendum

References

8. Bi-functional Redox Catalysis: Synthesis and Operation in Water-Cleavage Reactions

I. Introduction

II. Required Properties for Efficient Colloidal Semiconductors

III. Preparation and Characteristics of Colloidal Titanium Dioxide

IV. Photoinduced Redox Reactions

V. Colloidal Redox Catalysts

VI. Cyclic Water Cleavage with Bi-functional Redox Catalysts

VII. Increasing the Efficiency and the Sunlight Response

VII. Outlook

References

9. Examples for Photogeneration of Hydrogen and Oxygen from Water

I. Evolutions of H2 Induced by Visible Light in Sacrificial Systems

II. Evolution of O2 in Dark- and Light-Induced Processes in Sacrificial Systems

III. Hydrogen Evolution Induced by Light-Catalyzed Colloidal TiO2-Loaded Systems

IV. Design of Spinel- and Perovskite-Type Semiconductors Active in H2 Evolution Induced by Visible Light

References

10. Photosynthesis and Photocatalysis with Semiconductor Powders

I. Introduction

II. Photocatalytic Effect of Semiconductors

III. Photoassisted Decomposition of Water with Powdered Semiconductors

IV. Hydrogen Production from the Photocatalytic Reaction of Water and Organic Compounds

V. Hydrogen Production by Visible Light

VI. Energy Structure of the Ti02-Pt Particle and Its Photocatalytic Activity

VII. Application of Photocatalytic Reaction to Organic Synthesis

VIII. Summary

References

11. Photoelectrolysis of Water and Sensitization of Semiconductors

I. Introduction

II. Photoelectrolysis of Water with Semiconductors

III. Sensitization of Semiconductors: Chlorophyll-Sensitized Semiconductor Electrodes

References

12. Hydrogen-Generating Solar Cells Based on Platinum-Group Metal Activated Photocathodes

I. Scope

II. Requirements for Efficient Solar Hydrogen Generation

III. Solar Conversion Efficiency

IV. Chemical Stability of the Photocathode-Solution Interface

V. Radiationless Recombination of Photogenerated Electrons at the Photocathode-Electrolyte Interface

VI. The Relationship between the Fill Factor and the Overvoltage in Hydrogen-Evolving Solar Cells

VII. The Relationship between the Barrier Height and the Gain in Threshold Potential for Hydrogen Evolution

VIII. Stability of the Solar Conversion Efficiency

IX. Photoelectrolysis at High Levels of Irradiance

X. Photoelectrolytic Cells with p-lnP (Rh, H Alloy) Photocathodes

XI. Spontaneous Two-Photon Photoelectrolysis of HBr

XII. Conclusions

References

13. Photoelectrochemistry of Cadmium and Other Metal Chalcogenides in Polysulfide Electrolytes

I. Introduction

II. Interaction between CdS and Sulfide Ions in Solution

III. Stability of the CdSe-Polysulfide System

IV. Other Cadmium Chalcogenide-Polysulfide Systems

V. Zinc (and Zinc-Cadmium) Chalcogenides

VI. Other Metal Chalcogenides

VII. Polyselenide and Polytelluride Electrolytes

VIII. Surface Treatment of CdX Photoelectrodes

References

14. Electrically Conductive Polymer Layers on Semiconductor Electrodes

I. Introduction

II. Photoelectrochemical Devices: Principles and Definitions

III. Instability of n-Type Semiconductor Electrodes

IV. Experimental Considerations

V. Transport Properties

VI. Electrochemical Photovoltaic Cells

VII. Surface States and Interface Energetics

VIII. Photoelectrolysis of Water

IX. Guidelines for Control of Interface

References

15. Photochemical Fixation of Carbon Dioxide

I. Introduction

II. Energetics of Carbon Dioxide Reduction

III. Photochemical Fixation of Carbon Dioxide

IV. Electrochemical Reduction of Carbon Dioxide

V. Dynamics of Carbon Dioxide Reduction

VI. Photoelectrochemical Reduction of Carbon Dioxide

VII. Photoreduction of Carbon Dioxide with Semiconductors

VIII. Conclusions

References

16. Catalytic Nitrogen Fixation in Solution

I. Introduction

II. Peculiarities of the Thermodynamics of Molecular Nitrogen Reduction

III. Nitrogen Reduction in Aprotic Media

IV. Molecular Nitrogen Complexes with Transition-Metal Compounds and the Mechanism of Nitrogen Reduction in the Coordination Sphere of the Complex

V. Nitrogen Reduction in Protic Media

VI. Conclusion

References

Index