Sm-Induced Strain Heterogeneity Enables AEM-Dominated Oxygen Evolution on RuO ₂ for Proton Exchange Membrane Water Electrolysis

Ruthenium dioxide (RuO 2 ) exhibits high catalytic activity for the acidic oxygen evolution reaction (OER) in proton-exchange membrane water electrolysis (PEMWEs), yet its practical application is limited by sluggish kinetics and rapid degradation associated with lattice oxygen participation and Ru over-oxidation. Here, we present a strain-heterogeneity strategy to engineer an overall tensile lattice environment with localized compressive regions through samarium (Sm) doping RuO 2 (Sm-RuO 2 ) for enhanced OER activity and stability. In situ characterization combined with density functional theory (DFT) calculations reveal that strain heterogeneity suppresses lattice oxygen dissolution and weakens Ru-O covalency, while shortened Ru-Ru bonds near Sm atoms lower the kinetic barrier for the *O to *OOH conversion. Together, this strain-induced reconfiguration suppresses the lattice oxygen mechanism (LOM) and promotes an adsorbate evolution mechanism (AEM)-dominated pathway. Consequently, Sm-RuO 2 delivers an overpotential of only 189 mV at 10 mA cm −2 and maintains stable operation for over 500 h in the acidic electrolyte. When implemented in a PEMWE, Sm-RuO 2 operates stably for more than 200 h at 500 mA cm −2 with a low degradation rate of 0.12 mV h −1 . This work establishes 4f-metal-induced strain heterogeneity as an effective strategy for tuning the reaction pathways of Ru-based catalysts for the acidic OER.