Synergistic Effect of Tuning Reaction Mechanism and Interfacial Water for Efficient Acidic Water Oxidation

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Abstract
The development of active and durable acidic oxygen evolution reaction (OER) electrocatalysts is crucial for the commercialization of proton exchange membrane water electrolyzers (PEMWEs). Herein, we report a Ru‐substituted spinel Co 2 MnO 4 electrocatalyst (RuMnO), in which surface Co atoms are selectively replaced by Ru. This modification simultaneously tunes the reaction mechanism and interfacial water dynamics, synergistically enhancing OER kinetics. The formation of a short Ru─Ru bond length creates dual metal active sites that promote direct * OO * radical coupling, bypassing the conventional * OOH intermediate and suppressing lattice oxygen vacancy formation. Moreover, Ru substitution increases the fraction of free water molecules at the catalyst‐electrolyte interface, significantly accelerating the overall reaction kinetics. As a result, RuMnO achieves a low overpotential of 278 mV at 50 mA cm −2 and exhibits remarkable long‐term stability for 2500 h. Combined experimental and theoretical analyses reveal that RuMnO favors the oxide path mechanism (OPM) while simultaneously promoting the formation of interfacial free water. This study highlights the critical role of concurrently engineering the reaction mechanism and interfacial water dynamics to overcome the intrinsic limitations of acidic OER catalysis.

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