Efficient water oxidation catalysts based on readily available iron coordination complexes

Abstract

Water oxidation catalysis constitutes the bottleneck for the development of energy-conversion schemes based on sunlight. To date, state-of-the-art homogeneous water oxidation catalysis is performed efficiently with expensive, toxic and earth-scarce transition metals, but 3d metal-based catalysts are much less established. Here we show that readily available, environmentally benign iron coordination complexes catalyse homogeneous water oxidation to give O2, with high efficiency during a period of hours. Turnover numbers >350 and >1,000 were obtained using cerium ammonium nitrate at pH 1 and sodium periodate at pH 2, respectively. Spectroscopic monitoring of the catalytic reactions, in combination with kinetic studies, show that high valent oxo-iron species are responsible for the O–O forming event. A systematic study of iron complexes that contain a broad family of neutral tetradentate organic ligands identifies first-principle structural features to sustain water oxidation catalysis. Iron-based catalysts described herein open a novel strategy that could eventually enable sustainable artificial photosynthetic schemes

We thank R. Hage, X. Ribas and P. Lahuerta for reading this work and for comments. We thank the European Research Foundation for project FP7-PEOPLE-2010-ERG-268445 (J.Ll.), El Ministerio de Ciencia e Innovacion for project CTQ2009-08464 (M. C.), for a Ramon y Cajal contract (J.Ll.) and for a PhD grant (I. G-B.), Generalitat de Catalunya for an ICREA Academia Award and the European Research Council for Project ERC-2009-StG-239910 (M. C.)