Executive Summary : | The large-scale use of sunlight to produce hydrogen and oxygen could revolutionize fuel production, but the water oxidation reaction is kinetically challenging without a catalyst. The stepwise oxidation of water requires extra energy in the form of large overpotentials, which hinder the development of water-oxidation catalysts that can survive harsh oxidizing conditions. The current challenge is to develop artificial molecular Water-Oxidation Catalysts (WOCs) based on earth-abundant and cheap 3D-metals, which are highly efficient and have a turnover frequency comparable to Nature's OEC (100-400 times per second). These catalysts must be robust and survive the strong oxidizing environment in the presence of sacrificial oxidants during electrocatalysis without organic ligand oxidation and degradation. The authors propose two approaches to increase the rate of desired catalysis for water oxidation: increasing the rate of desired catalysis through the association of M-OH2 groups and redox active ligands, and slowing the rate of undesired catalyst degradation through the use of N-heterocyclic carbenes (NHCs) as ligand architectures. Typical experiments involve synthesizing cobalt NHC complexes and evaluating them as WOCs. Immobilizing a soluble catalyst on an electrode can be useful for electrochemical studies, but durability, surface coverage, electron transfer rates, efficiencies, and altered interactions between redox centers will also be considered. A host of stoichiometric reactions, real-time spectroscopic analyses, intermediate trapping, isotope labeling, and kinetic studies will be undertaken to address these points. Computational studies will provide credence to the mechanism. |