A New Water-Soluble Copper(II) Coordination Polymer for Electrocatalytic Oxygen Evolution Reaction

The development of efficient and low-cost catalysts to promote the oxygen evolution reaction (OER) is a challenge for the generation of green hydrogen through water splitting electrolysis. This work describes the synthesis of a new water-soluble one-dimensional copper(II) coordination polymer for application as an earth-abundant OER molecular electrocatalyst. The ligand was designed to have nitrogenated and carboxylate groups, inspired by the amino acid residues of the Mn4CaO5 cluster of photosystem II (PSII). The multiple coordination sites with different Lewis basicity were envisioned to infer structural stability and modulated electronic structure of the Cu(II) center allowing redox processes to occur during the OER. Furthermore, a N-propanoate linker allows structural flexibility for the formation of carboxylate bridges and the coordination polymer. The single-crystal diffraction structure reveals an unusual monatomic bridge involving the chelation of the carboxylate group to two adjacent Cu(II) ions. The electrocatalysis of the OER was conducted in a phosphate buffer at pH 12.5, and an onset overpotential of 394 mV was achieved at a current density of 0.1 mA cm–2, comparable to those reported for CuII molecular catalysts. Kinetic data show first-order electron transfer with a turnover frequency of 2.1 s–1. Stability tests by chronopotentiometry and cyclic voltammetry showed the formation of a CuOx-OH film at the working electrode surface, indicating the contribution of heterogeneous electrocatalysis for the OER.