ABSTRACT
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. Before further progress can be made in the field of water splitting, significant developments in the catalysis of oxygen evolution are needed. Herein we present an iron-centered tetraamido macrocyclic ligand (Fe-TAML) that efficiently catalyzes the oxidative conversion of water to dioxygen. When the catalyst is combined in unbuffered solution with ceric ammonium nitrate, its turnover frequency exceeds 1.3 s(-1). Real-time UV-vis and oxygen monitoring of the active complex give insights into the reaction and decay kinetics.
ABSTRACT
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. the water gas shift reaction, halogen acid splitting, or water splitting. This article endeavors to define a common context for these research topics, particularly by analyzing the thermodynamic boundaries of photosynthesis. Specifically, the generalized efficiency restrictions on both light absorption and energy storage are expounded, the analogous limitations for several individual photosynthetic strategies are stated, several synthetic catalyst architectures are highlighted, the advantages of molecular and macroscopic approaches are discussed, and key figures of merit are presented.
ABSTRACT
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.
ABSTRACT
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. The importance of these catalysts lies in (A) their ability to oxidize water in a purely aqueous medium, (B) their simplicity of design, (C) their durability, and (D) the ease with which they can be tuned to accommodate the electrochemical needs of photosensitizers in hypothetical photochemical water oxidation and full artificial photosynthetic schemes.
ABSTRACT
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. This simplified approach allows the characterization of degradation products that are otherwise obscured in more complex systems. A novel 16-well setup for parallel kinetic analysis of H2 evolution enables high-throughput screening of reaction conditions and quantization of the decaying reaction rate. DFT calculations rationalize the differences between this and previous studies on tris-diimine ruthenium(II) photosensitizers.