Interstitial‐Substitutional‐Mixed Solid Solution of RuO ₂ Nurturing a New Pathway Beyond the Activity‐Stability Linear Constraint in Acidic Water Oxidation

Abstract The acidic oxygen evolution reaction (OER) electrocatalysts for proton exchange membrane electrolyzer (PEMWE) often face a trade‐off between activity and stability due to inherent linear relationship and overoxidation of metal atoms in highly oxidative environments, while following the conventional adsorbate evolution mechanism (AEM). Herein, a favorable AEM‐derived proton acceptor‐electron donor mechanism (PAEDM) is proposed in RuO ₂ by constructing interstitial‐substitutional mixed solid solution structure (denoted as C,Ta‐RuO ₂ ), which can effectively break the activity‐stability trade‐off of RuO ₂ in acidic OER. In situ spectroscopy experiments and theoretical calculations reveal that the interstitial C as the proton acceptor reduces the deprotonation energy barrier, enhancing catalytic activity, while the substitutional Ta as the electron donor donates electrons to the Ru sites via bridging oxygen, weakening the Ru─O bond covalency and preventing over‐oxidation of surface Ru, thereby ensuring long‐term stability. Under the guidance of this mechanism, the optimized C,Ta‐RuO ₂ simultaneously achieves far low overpotential (η ₁₀ = 171 mV) and ultra‐long stability (over 1300 h) for the acidic OER. More remarkably, a homemade PEMWE using C,Ta‐RuO ₂ as the anode also shows high water splitting performance (1.63 V@1 A cm ⁻² ). This work supplies a novel strategy to guide future developments on efficient OER electrocatalysts toward water oxidation.