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...

/pdf/proton-coupled-electron-transfer-3oyvp0w9qd.pdf

Proton-Coupled Electron Transfer

Photosystem II (PSII) is the water splitting enzyme of photosynthesis. Its appearance during evolution dramatically changed the chemical composition of our planet and set in motion an unprecedented explosion in biological activity. Powered by sunlight, PSII supplies biology with the ‘hydrogen’ needed to convert carbon dioxide into organic molecules. The questions now are can we continue to exploit this photosynthetic process through increased use of biomass as an energy source and, more importantly, can we address the energy/CO2 problem by developing new photochemical technologies which mimic the natural system? (Critical review, 82 references)

Photosynthetic energy conversion: natural and artificial

We introduce density functional theory and review recent progress in its application to transition metal chemistry. Topics covered include local, meta, hybrid, hybrid meta, and range-separated functionals, band theory, software, validation tests, and applications to spin states, magnetic exchange coupling, spectra, structure, reactivity, and catalysis, including molecules, clusters, nanoparticles, surfaces, and solids.

Density functional theory for transition metals and transition metal chemistry

Many, if not most, redox reactions are coupled to proton transfers. This includes most common sources of chemical potential energy, from the bioenergetic processes that power cells to the fossil fuel combustion that powers cars. These proton-coupled electron transfer or PCET processes may involve multiple electrons and multiple protons, as in the 4 e–, 4 H+ reduction of dioxygen (O2) to water (eq 1), or can involve one electron and one proton such as the formation of tyrosyl radicals from tyrosine residues (TyrOH) in enzymatic catalytic cycles (eq 2). In addition, many multi-electron, multi-proton processes proceed in one-electron and one-proton steps. Organic reactions that proceed in one-electron steps involve radical intermediates, which play critical roles in a wide range of chemical, biological, and industrial processes. This broad and diverse class of PCET reactions are central to a great many chemical and biochemical processes, from biological catalysis and energy transduction, to bulk industrial chemical processes, to new approaches to solar energy conversion. PCET is therefore of broad and increasing interest, as illustrated by this issue and a number of other recent reviews.

/pdf/thermochemistry-of-proton-coupled-electron-transfer-reagents-v04esq6den.pdf

Thermochemistry of Proton-Coupled Electron Transfer Reagents and its Implications

The blue dimer, cis, cis-[(bpy)2(H2O)Ru(III)ORu(III)(H2O)(bpy)2](4+), is the first designed, well-defined molecule known to function as a catalyst for water oxidation. It meets the stoichiometric requirements for water oxidation, 2H2O --> -4e(-), -4H(+) O-O, by utilizing proton-coupled electron-transfer (PCET) reactions in which both electrons and protons are transferred. This avoids charge buildup, allowing for the accumulation of multiple oxidative equivalents at the Ru-O-Ru core. PCET and pathways involving coupled electron-proton transfer (EPT) are also used to avoid high-energy intermediates. Application of density functional theory calculations to molecular and electronic structure supports the proposal of strong electronic coupling across the micro-oxo bridge. The results of this analysis provide explanations for important details of the descriptive chemistry. Stepwise e(-)/H(+) loss leads to the higher oxidation states [(bpy)2(O)Ru(V)ORu(IV)(O)(bpy)2] (3+) (Ru(V)ORu(IV)) and [(bpy)2(O)Ru(V)ORu(V)(O)(bpy)2](4+) (Ru(V)ORu(V)). Both oxidize water, Ru(V)ORu(IV) stoichiometrically and Ru(V)ORu(V) catalytically. In strongly acidic solutions (HNO3, HClO4, and HSO3CF3) with excess Ce(IV), the catalytic mechanism involves O---O coupling following oxidation to Ru(V)ORu(V), which does not build up as a detectable intermediate. Direct evidence has been found for intervention of a peroxidic intermediate. Oxidation of water by Ru(V)ORu(IV) is far slower. It plays a role late in the catalytic cycle when Ce(IV) is depleted and is one origin of anated intermediates such as [(bpy)2(HO)Ru(IV)ORu(IV)(NO3)(bpy)2](4+), which are deleterious in tying up active components in the catalytic cycle. These intermediates slowly return to [(bpy)2(H2O)Ru(IV)ORu(III)(OH2)(bpy)2](5+) with anion release followed by water oxidation. The results of a recent analysis of water oxidation in the oxygen-evolving complex (OEC) of photosystem II reveal similarities in the mechanism with the blue dimer and significant differences. The OEC resides in the thylakoid membrane in the chloroplasts of green plants, and careful attention is paid in the structure to PCET, EPT, and long-range proton transfer by sequential local proton transfers. The active site for water oxidation is a CaMn 4 cluster, which includes an appended Mn site, Mn(4), where O---O coupling is thought to occur. Photochemical electron transfer results in oxidation of tyrosine Y Z to Y Z (.), which is approximately 7 A from Mn(4). It subsequently oxidizes the OEC through the stepwise stages of the Kok cycle. O---O coupling appears to occur through an initial peroxidic intermediate formed by redox nucleophilic attack of coordinated OH(-) in Ca-OH(-) on Mn (IV)=O.

Mechanisms of water oxidation from the blue dimer to photosystem II

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Mechanisms of water oxidation from the blue dimer to photosystem II