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A Fast Soluble Carbon-Free Molecular Water Oxidation Catalyst Based on Abundant Metals

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Science  11 Mar 2010:
1185372
DOI: 10.1126/science.1185372

Abstract

Traditional homogeneous water oxidation catalysts are plagued by instability under the reaction conditions. We report that the complex [Co4(H2O)2(PW9O34)2]10- (1) comprising a Co4O4 core stabilized by oxidatively resistant polytungstate ligands, is a hydrolytically and oxidatively stable homogeneous water oxidation catalyst that self-assembles in water from salts of earth abundant elements (Co, W, and P). With [Ru(bpy)3]3+ (bpy = 2,2’-bipyridine) as the oxidant, we observe catalytic turnover frequencies for O2 production ≥ 5 s-1 at pH 8. The rate’s pH sensitivity reflects the pH dependence of the 4-electron H2O/O2 couple. Extensive spectroscopic, electrochemical, and inhibition studies firmly indicate that 1 is stable under catalytic turnover conditions: Neither hydrated cobalt ions nor cobalt hydroxide/oxide particles form in situ.