Ni─Nb Synergistic Regulation in RuO 2 Nanocrystals Enables Efficient and Stable Acidic Water Oxidation

The activity‐stability trade‐off of RuO 2 ‐based catalysts in the acidic oxygen evolution reaction (OER) remains a major bottleneck for proton exchange membrane water electrolysis (PEMWE). Herein, a synergistic bimetallic codoping strategy was proposed to harness the complementary benefits of high‐valence Nb and low‐valence Ni dopants. The resulting NiNb‐RuO 2 catalyst exhibits outstanding OER performance in acidic media, delivering an ultralow overpotential of 157 mV at 10 mA cm −2 and stable operation for 200 h at 100 mA cm −2 , outperforming most reported Ru‐based catalysts. Remarkably, it also demonstrates excellent stability at a current density of 250 mA cm −2 over 200 h under PEMWE operations at 60 °C. Combined with density functional theory (DFT) calculations and in situ characterizations, a distinct Ni─Nb synergistic mechanism reveals that Nb suppresses lattice oxygen activation and mitigates structural degradation, while Ni regulates the electron‐withdrawing capability of Ru sites to optimize the adsorption of *OOH intermediates, thereby accelerating OER kinetics through the AEM pathway. This work provides an effective strategy for simultaneously enhancing the activity and durability of RuO 2 ‐based catalysts toward practical PEMWE applications.