Solar fuels: thermodynamics, candidates, tactics, and figures of merit.

Inorganic chemistry has been and continues to be a central discipline in the field of renewable energy and solar fuels. A fundamental approach to storing solar energy is artificial photosynthesis, whereby uphill chemical reactions are driven by light, e.g.

Fast water oxidation using iron.

Photolysis of water, a long-studied strategy for storing solar energy, involves two half-reactions: the reduction of protons to dihydrogen and the oxidation of water to dioxygen. Proton reduction is well-understood, with catalysts achieving quantum yields of 34% when driven by visible light. Water oxidation, on the other hand, is much less advanced, typically involving expensive metal centers and rarely working in conjunction with a photochemically powered system.

Polyoxometalate embedding of a tetraruthenium(IV)-oxo-core by template-directed metalation of [gamma-SiW10O36]8-: a totally inorganic oxygen-evolving catalyst.

Solid state and solution evidence confirms the embedding of an adamantane-like, Ru4O6 fragment by the divacant, gamma-decatungstosilicate ligand. The resulting complex catalyzes water oxidation to oxygen with TON up to 500 and TOF > 450 h-1.

Cyclometalated iridium(III) Aquo complexes: efficient and tunable catalysts for the homogeneous oxidation of water.

A series of bis-phenylpyridine, bis-aquo iridium(III) complexes is herein shown to robustly and efficiently catalyze the oxidation of water to dioxygen in the presence of a sacrificial oxidant. Through substitution on the cyclometalating ligands of these complexes, it is shown that a broad range of oxidation potentials can be achieved within this class of catalyst. Parallel, dynamic monitoring of oxygen evolution, made possible by equipping reaction vessels with pressure-voltage transducers, facilitates correlation of these complexes' ionization potentials with their respective activity toward water oxidation.

Visible light induced catalytic water reduction without an electron relay.

Protons from water are reduced by a catalytic system composed of a heteroleptic iridium(III) photosensitizer [Ir(ppy)2(bpy)]+, platinum catalyst, and sacrificial reductant. The hydrogen quantum yield reaches 0.26 in this study, which proceeds via reductive quenching of the excited photosensitizer by triethanolamine.