Octanuclear Cu(ii) cluster–tungstosilicate composite as efficient electrocatalyst for oxygen evolution reaction at near-neutral pH

Abstract

Transition metal clusters have been used for water oxidation with high catalytic efficiency. However, they are water-soluble and often used homogeneously rather than heterogeneously. Herein, a water-soluble octanuclear Cu(II) cluster was heterogenized by binding it with α-undecatungstosilicate [α-SiW₁₁O₃₉]⁸⁻via the electrostatic effect. Octanuclear cluster [Cu₈(dpk·OH)₈(OAc)₄]⁴⁺ (dpk·OH = monoanion of the hydrated, gem-diol form of di-2-pyridyl ketone) was transformed into insoluble [Cu₈(dpk·OH)₈(OAc)₄]₂@[α-SiW₁₁O₃₉] (1) composite. This composite catalyzes water electro-oxidation efficiently with an onset potential of only 370 mV and attains a catalytic current density of 1 mA cm⁻² at a low overpotential of 580 mV with a Tafel slope value of 62 mV per decade at near-neutral pH. Electrochemical measurements and spectroscopy characterization indicate that this composite remains stable and active after prolonged electrolysis experiments. This work reveals that the electrostatic interaction between transition metal complexes and polyoxoanions is a feasible and convenient method to synthesize efficient heterogenized homogeneous water oxidation catalysts (WOCs).