Electrochemical water oxidation using a copper complex

Abstract

This study highlights the importance of proton coupled electron transfer (PCET) during electrochemical-driven water oxidation catalysis employing a copper complex.

Herein, we report the application of the mononuclear copper complex 1 , [Cu II (L)] 2+ , in electrochemical water oxidation catalysis (L = 1,3-bis(((1-methyl-1 H -imidazol-2-yl)methyl)amino)propan-2-ol). The complex exhibits a N 4 donor set consisting of two amine and two imidazole units and a dangling OH unit in close proximity to the copper ion. 1 exhibits a moderate apparent rate constant k cat of 0.12 s −1 in catalysis and operates at an overpotential of 0.83 V. Detailed investigations allowed us to derive a mechanism for water oxidation. The catalysis proceeds only under basic conditions, where [Cu II (L)(OH)] + , 1 H −1 , is the main solution species, which indicates that a negatively charged ligand is necessary to drive the catalysis. Initial oxidation of 1 H −1 is coupled to proton loss forming a copper( iii ) species and further oxidation initiates oxygen evolution. Initial oxidation of 1 under neutral, i.e. non-catalytic, conditions is pH independent, highlighting the importance of PCET steps during catalysis. We collected reasonable evidence that catalysis proceeds via a water nucleophilic attack mechanism. The electrolyte presumably acts as a proton acceptor in catalysis as the onset potential depends on the buffer employed.