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 Cu^II 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.