Photosystem II Inspired NiFe-Based Electrocatalysts for Efficient Water Oxidation via Second Coordination Sphere Effect

Abstract

The mismatched fast-electron-slow-proton process in the electrocatalytic oxygen evolution reaction (OER) severely restricts the catalytic efficiency. To overcome these issues, accelerating the proton transfer and elucidating the kinetic mechanism are highly sought after. Herein, inspired by photosystem II, we develop a family of OER electrocatalysts with FeO₆ /NiO₆ units and carboxylate anions (TA^2- ) in the first and second coordination sphere, respectively. Benefiting from the synergistic effect of the metal units and TA^2- , the optimized catalyst delivers superior activity with a low overpotential of 270 mV at 200 mA cm^-2 and excellent cycling stability over 300 h. A proton-transfer-promotion mechanism is proposed by in situ Raman, catalytic tests, and theoretical calculations. The TA^2- (proton acceptor) can mediate proton transfer pathways by preferentially accepting protons, which optimizes the O-H adsorption/activation process and reduces the kinetic barrier for O-O bond formation.

Keywords: Metal-Organic Frameworks; Oxygen Evolution Reaction; Proton Transfer; Second Coordination Sphere.