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Constructing atomically coupled W–O–Ru interfacial units on RuO2 triggers a dynamic strain evolution during the oxygen evolution reaction. An initial tensile strain secures structural stability, while a self-adjusting transition to interfacial compression optimizes catalytic activity. This dynamic strain engineering effectively decouples the long-standing activity-stability trade-off, enabling highly efficient and durable acidic water oxidation. ABSTRACT Developing highly active and durable acidic oxygen evolution reaction (OER) electrocatalysts remains a central challenge for proton-exchange membrane water electrolysis (PEMWE). Here, we combine theory-guided design, atomic-layer engineering, and operando spectroscopy to create a structurally robust, mechanistically tuned Ru-based catalyst. Density functional theory reveals that depositing W1O3 onto RuO2 maximizes Ru and O vacancy formation energies, outperforming other tested transition metals. Guided by this, we employ atomic layer deposition to construct atomically coupled W–O–Ru interfacial units on RuO2 (W–O–RuO2), generating a tensile-stressed surface while preserving the rutile core. Comprehensive in situ spectroscopy and mass spectrometry demonstrate that this architecture effectively suppresses lattice–oxygen activation, shifting the reaction from a lattice–oxygen mechanism to a more reversible adsorbate evolution mechanism. Operando x-ray absorption spectroscopy confirms the dynamic stability of the W–O–Ru interface during OER, which evolves into a resilient, mildly compressive (1%) state without degrading. Consequently, W–O–RuO2 demands a mere 168 mV overpotential at 10 mA cm− 2 and sustains 1 A cm− 2 in a PEMWE device for 1000 h with an ultra-low degradation rate of 63.3 µV/h. This work establishes interfacial unit engineering as a generalizable blueprint for designing exceptionally stable acidic OER catalysts.