Homogeneous Electrochemical Water Oxidation at Neutral pH by Water‐Soluble Ni II Complexes Bearing Redox Non‐innocent Tetraamido Macrocyclic Ligands

Water oxidation is the bottleneck reaction in artificial photosynthesis. Exploring highly active and stable molecular water oxidation catalysts (WOCs) is still a great challenge. In this study, a water‐soluble Ni II complex bearing a redox non‐innocent tetraamido macrocyclic ligand (TAML) is found to be an efficient electrocatalyst for water oxidation in neutral potassium phosphate buffer. Controlled‐potential electrolysis experiments show that it can sustain at a steady current of approximately 0.2 mA cm −2 for >7 h at 1.75 V versus normal hydrogen electrode (NHE) without the formation of NiO x . Electrochemical and spectroelectrochemical tests show that the redox‐active ligand, as well as HPO 4 2− in the buffer, participate in the catalytic cycle. More importantly, catalytically active intermediate [Ni III (TAML 2− )−O . ] is formed via several proton‐coupled electron transfer processes and reacts with H 2 O with the assistance of base to release molecular oxygen. Thus, the employment of redox non‐innocent ligands is a useful strategy for designing effective molecular WOCs.