A Nickel(II) Complex as a Homogeneous Electrocatalyst for Water Oxidation at Neutral pH: Dual Role of HPO42− in Catalysis

A new mononuclear nickel complex, featuring two cis‐relative labile sites, is reported as a homogeneous electrocatalyst for water oxidation in a neutral phosphate buffer. The water oxidation catalysis can be initiated at a moderate overpotential of approximately 0.48 V. Mechanistic studies reveal that the oxidation of water by a two‐electron oxidized species of the nickel catalyst is feasible, with formation of a peroxide intermediate through intramolecular O−O coupling. Interestingly, it has been found that the buffer base (HPO42−) plays a dual role in the catalytic system: it acts as a proton acceptor to expedite proton‐coupled electron transfer (PCET) during catalysis, but it also suppresses the electrocatalysis through an anation process. Dual role of HPO42−: A nickel(II) complex is reported as a robust homogeneous electrocatalyst for water oxidation at mild conditions, following a catalytic mechanism described by electrochemical studies and DFT calculations. Interestingly, it has been found that HPO42− plays a dual role, both positive and negative, in the electrocatalysis with the nickel complex.