Electro- and photo-chemical driven water reduction catalyzed by a cobalt(III) complex with high turnover number

•Reaction of CoCl2 and a amine-bis(phenolate) ligand (H2L) affords a cobalt(III) complex [LCoCl] 1.•1 can electrocatalyze hydrogen evolution from water with a TOF of 230 moles/mole/h.•In the presence of blue light, 1 produces hydrogen with a TON of 4130 mol of H2 (mol of cat)−1.

A new catalyst based on a cobalt complex [LCoCl] 1 is formed by the reaction of dimethylaminoethylamino-N,N-bis(2-methylene-4-tert-butyl-6-methyl) phenol (H2L) with CoCl2·6H2O for both electrolytic and photolytic water reduction. 1 can electrocatalyze hydrogen evolution from water with a turnover frequency (TOF) of 230 moles of hydrogen per mole of catalyst per hour at an overpotential of 689 mV (pH 7.0). Additionally, under photoirradiation with blue light (λmax = 469 nm), 1, together with [Ru(bpy)3]Cl2 and ascorbic acid in a pH 6.0 aqueous solution, also produces hydrogen with a remarkable turnover number (TON) of 4130 mol of H2 per mol of catalysts. This performance is different from the reported results that the best pH for photocatalytic H2 evolution by photo-catalyst was observed at pH 4.0. This discovery has established a new chemical paradigm for creating water reduction catalyst that is highly active near neutral media.

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