Tianrui Xue, Zhuoran Liu, Yiting Song, Miaomiao Liu, Jian Zhang, Kai Zhou, Yongjun Shen, Xiaoqing Mao, Xiaozhi Su, Hui Li, Chunzhong Li
Abstract Designing acid‐stable RuO 2 catalysts capable of overcoming the activity‐stability trade‐off remains pivotal for advancing proton exchange membrane water electrolyzers (PEMWEs). Here, we introduce a cation‐vacancy engineering strategy to generate localized compressive strain in RuO 2 by electrochemically leaching Cd from a pre‐doped lattice. This strain modulation simultaneously elevates the Ru valence state (+4.35) and strengthens Ru─O covalent bonds, optimizing *OH/*O/*OOH adsorption energetics while suppressing over‐oxidation. The resulting V Cd ‐RuO 2 catalyst achieves an overpotential of 203 mV at 10 mA cm −2 in 0.1 M HClO 4 . Integrated into a PEMWE, it sustains >600 h operation at 200 mA cm −2 with a voltage degradation rate of 0.1 mV h −1 . The MEA based on V Cd ‐RuO 2 required cell voltages outperformed commercial RuO 2 by 120–180 mV at industrially relevant current densities (0.5–1.5 A cm −2 ), thereby demonstrating significant energy efficiency. Multiscale analyses confirm that compressive strain stabilizes high‐valence Ru sites through enhanced orbital overlap, reconciling catalytic activity with structural durability. This work establishes vacancy‐driven strain engineering as a universal approach for designing robust, Ir‐free OER electrocatalysts.