A Glutamate-Enabled Proton Relay in a Bioinspired Cu ₄ O ₄ Cubane Boosts Neutral Water Oxidation via Proton-Coupled Electron Transfer

The oxygen evolution reaction under neutral conditions remains a significant challenge due to sluggish kinetics and catalyst instability, largely stemming from inefficient proton management. Inspired by the proton-coupled electron transfer (PCET) networks in the oxygen-evolving complex of photosystem II, we report the rational design of two bioinspired cubane-type tetranuclear copper catalysts, Cu₄(L_Gly)₄ and Cu₄(L_Glu)₄, functionalized with amino acid derivatives. Electrochemical studies reveal that the glutamate-modified Cu₄(L_Glu)₄ outperforms its glycine counterpart, achieving a remarkable turnover frequency (TOF) of 9.64 ± 0.07 s^-1 at a low overpotential of 0.63 V in phosphate buffer solution (pH 7.30). Differential pulse voltammetry and mechanistic investigations indicate a PCET nature for the copper redox transitions. Density functional theory calculations demonstrate that the carboxylate group of the glutamate residue acts as an intrinsic proton relay, significantly lowering the energy barrier for the critical O-O bond formation step. Furthermore, a photovoltaic-electrocatalytic (PV-EC) device utilizing the Cu₄(L_Glu)₄ anode achieves a solar-to-hydrogen (STH) conversion efficiency of 10.24% under neutral conditions, one of the highest reported values without a strong alkaline environment. This work underscores the critical role of second-sphere proton-transfer functionality in designing efficient molecular catalysts for PCET-driven energy conversion reactions.