Phase-heterogeneous RuO_x overcomes the activity-stability trade-off in acidic water oxidation

Ruthenium dioxide (RuO₂) is among the most active catalysts for the acidic oxygen evolution reaction (OER), yet its practical deployment is severely limited by rapid deactivation arising from two intertwined degradation pathways: (i) irreversible lattice oxygen oxidation via the lattice oxygen mechanism (LOM), which induces structural collapse, and (ii) electrochemical overoxidation of surface Ru⁴⁺ to soluble high-valent species (e.g., Ru⁶⁺/Ru⁸⁺). Conventional doping strategies often compromise intrinsic activity or introduce leachable components, highlighting the urgent need for a dopant-free stabilization approach. Herein, we demonstrate that engineering a crystalline-amorphous phase heterogeneity in pure RuO_x intrinsically decouples activity from instability. The resulting heterogeneous catalyst (CA-RuO_x) selectively promotes the conventional adsorbate evolution mechanism (AEM) while effectively suppressing LOM-driven oxygen loss, as evidenced by operando differential electrochemical mass spectrometry coupled with ¹⁸O isotope labeling experiments. This dual regulation stabilizes low-valent Ru sites against overoxidation without sacrificing redox activity, enabling a low overpotential of 194 ± 5 mV at 10 mA cm^-2 and exceptional durability (>430 h) in acid. Our work establishes phase heterogeneity as an efficient dopant-free design strategy to overcome the activity-stability trade-off in Ru-based OER electrocatalysts.