https://zenodo.org/record/1258475/files/article.pdf

Electron transfers in chemistry and biology

1. Setting the Scope of the Challenge 6474 1.1. The Need for Solar Energy Supply and Storage 6474 1.2. An Imperative for Discovery Research 6477 1.3. Scope of Review 6478 2. Large-Scale Centralized Energy Storage 6478 2.1. Pumped Hydroelectric Energy Storage (PHES) 6479 2.2. Compressed Air Energy Storage (CAES) 6480 3. Smaller Scale Grid and Distributed Energy Storage 6481 3.1. Flywheel Energy Storage (FES) 6481 3.2. Superconducting Magnetic Energy Storage 6482 4. Chemical Energy Storage: Electrochemical 6482 4.1. Batteries 6482 4.1.1. Lead-Acid Batteries 6483 4.1.2. Alkaline Batteries 6484 4.1.3. Lithium-Ion Batteries 6484 4.1.4. High-Temperature Sodium Batteries 6484 4.1.5. Liquid Flow Batteries 6485 4.1.6. Metal-Air Batteries 6485 4.2. Capacitors 6485 5. Chemical Energy Storage: Solar Fuels 6486 5.1. Solar Fuels in Nature 6486 5.2. Artificial Photosynthesis and General Considerations of Water Splitting 6486

Solar Energy Supply and Storage for the Legacy and Nonlegacy Worlds

▪ Abstract Proton-coupled electron transfer (PCET) is an important mechanism for charge transfer in a wide variety of systems including biology- and materials-oriented venues. We review several are...

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Proton-Coupled Electron Transfer

Striving for new solar fuels, the water oxidation reaction currently is considered to be a bottleneck, hampering progress in the development of applicable technologies for the conversion of light into storable fuels. This review compares and unifies viewpoints on water oxidation from various fields of catalysis research. The first part deals with the thermodynamic efficiency and mechanisms of electrochemical water splitting by metal oxides on electrode surfaces, explaining the recent concept of the potential-determining step. Subsequently, novel cobalt oxide-based catalysts for heterogeneous (electro)catalysis are discussed. These may share structural and functional properties with surface oxides, multinuclear molecular catalysts and the catalytic manganese–calcium complex of photosynthetic water oxidation. Recent developments in homogeneous water-oxidation catalysis are outlined with a focus on the discovery of mononuclear ruthenium (and non-ruthenium) complexes that efficiently mediate O2 evolution from water. Water oxidation in photosynthesis is the subject of a concise presentation of structure and function of the natural paragon—the manganese–calcium complex in photosystem II—for which ideas concerning redox-potential leveling, proton removal, and OO bond formation mechanisms are discussed. The last part highlights common themes and unifying concepts.

The Mechanism of Water Oxidation: From Electrolysis via Homogeneous to Biological Catalysis

The goal of artificial photosynthesis is to use the energy of the sun to make high-energy chemicals for energy production. One approach, described here, is to use light absorption and excited-state electron transfer to create oxidative and reductive equivalents for driving relevant fuel-forming half-reactions such as the oxidation of water to O2 and its reduction to H2. In this “integrated modular assembly” approach, separate components for light absorption, energy transfer, and long-range electron transfer by use of free-energy gradients are integrated with oxidative and reductive catalysts into single molecular assemblies or on separate electrodes in photelectrochemical cells. Derivatized porphyrins and metalloporphyrins and metal polypyridyl complexes have been most commonly used in these assemblies, with the latter the focus of the current account. The underlying physical principleslight absorption, energy transfer, radiative and nonradiative excited-state decay, electron transfer, proton-coupled elec...

Chemical approaches to artificial photosynthesis

Structure and redox properties of the water-oxidation catalyst [(bpy)2(OH2)RuORu(OH2)(bpy)2]4+

Water oxidation by [(bpy)2(O)RuVORuV(O)(bpy)2] 4+. An oxygen-labeling study

Redox and spectral properties of the cis and trans isomers of the osmium(VI) dioxo complex [(bpy)2Os(O)2](ClO4)2

Stereoselectivity in electron-transfer reactions

The oxo-bridged Os dimer ((bpy)/sub 2/(H/sub 2/O)Os/sup III/OOs/sup IV/(OH)(bpy)/sub 2/)/sup 4 +/ has been isolated and characterized. Electrochemical experiments in aqueous solution have revealed an extensive redox chemistry for the dimer. The pH dependences of the potentials for the series of couples are presented and compared to those of the corresponding Ru dimer. The electrochemical results shed considerable light on the role of pH and electronic effects in stabilizing or destabilizing various oxidation states in the thermodynamic sense, in defining decomposition pathways, and in giving insight into the role that the thermodynamic properties of the various oxidation states have in dictating the reactivity properties of the dimers.

Daniel A. Geselowitz

Papers

Structure and redox properties of the water-oxidation catalyst [(bpy)2(OH2)RuORu(OH2)(bpy)2]4+

Water oxidation by [(bpy)2(O)RuVORuV(O)(bpy)2] 4+. An oxygen-labeling study

Redox and spectral properties of the cis and trans isomers of the osmium(VI) dioxo complex [(bpy)2Os(O)2](ClO4)2

Stereoselectivity in electron-transfer reactions

Redox properties of the oxo-bridged osmium dimer [(bpy)2(OH2)OsIIIOOsIV(OH)(bpy)2]4+. Implications for the oxidation of water to oxygen