Efficient Homogeneous Electrocatalytic Water Oxidation by a Manganese Cluster with Overpotential of Only 74 mV

Water electrolysis is among the simplest method for generating hydrogen as an alternative renewable fuel. A major challenge associated with this process is the development of cheap, simple and environmentally benign catalysts for water oxidation that lead to a minimum overpotential. Inspired by the Mn4CaOx cluster that catalyzes water oxidation in photosystem II, we describe here the synthesis and characterization of the manganese cluster [Mn12O12(O2CC6H2(OH)3)16(H2O)4] (Mn12TH) along with its electrocatalytic activity at pH 6. Electrochemical, spectroscopic and electron microscopy studies show that Mn12TH is a homogeneous electrocatalyst for water oxidation, which enables oxygen evolution with a reaction rate of 22 s‐1, high Faradic efficiency (93%) and an overpotential of only 74 mV, the lowest reported to date. Based on our electrochemical data, we suggest that the organic ligands, which can be described as the second coordination sphere of the catalytic manganese core, play a key role in facilitating the oxidation process and accelerating the reaction.

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