Ni─Nb Synergistic Regulation in RuO2 Nanocrystals Enables Efficient and Stable Acidic Water Oxidation.

The activity-stability trade-off of RuO2-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-RuO2 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 RuO2-based catalysts toward practical PEMWE applications.