Water oxidation is the key half reaction to achieve full splitting of water to hydrogen and oxygen.Herein,a binuclear complex,[(L4-)Co2Ⅲ(OH)]ClO4,was reported as a stable and efficient homogenous catalyst for electrocatalytic water oxidation in 0.1 M phosphate buffer (pH 7.0).Cyclic voltammetry experiments indi-cated that the catalytic process proceed via "one-site catalysis with two-sites oxidation" mechanism in which both two metal sites store the required oxidation equivalents for water oxidation and O-O bond for-mation occurs by single-site water nucleophilic attack (WNA).