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

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Science  16 Apr 2010:
Vol. 328, Issue 5976, pp. 342-345
DOI: 10.1126/science.1185372

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Traditional homogeneous water oxidation catalysts are plagued by instability under the reaction conditions. We report that the complex [Co4(H2O)2(PW9O34)2]10–, 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 is 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 four-electron O2-H2O couple. Extensive spectroscopic, electrochemical, and inhibition studies firmly indicate that [Co4(H2O)2(PW9O34)2]10– is stable under catalytic turnover conditions: Neither hydrated cobalt ions nor cobalt hydroxide/oxide particles form in situ.

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