The development of efficient homogeneous water oxidation catalysts (WOCs) is an important issue for hydrogen production via water splitting. Copper complexes with well-defined structures are widely studied but the overpotential is usually high, especially under neutral conditions. In this article, we report a mononuclear tetracoordinated copper complex [Cu^II(L)](ClO₄)₂ (1, L = hexaaza macrotricyclic ligand 1,3,6,9,11,14-hexaazatricyclo[12.2.1.1^6,9]octadecane) as an efficient homogeneous catalyst for electrochemical water oxidation in phosphate-buffered solution under neutral conditions. Complex 1 exhibits satisfactory stability and activity and oxygen evolution occurs with an onset overpotential of 480 mV, which is much lower than most typical Cu-based homogeneous WOCs. Meanwhile, a turnover frequency of 3.65 s⁻¹ is comparable with some molecular Cu containing electrocatalysts reported so far.