Constructing Built‐in Hydroxyl Relay Through Ru/RuO 2 Interfaces for Efficient PEM Water Electrolysis

As promising non‐iridium alternatives, RuO 2 ‐based catalysts demonstrate superior acidic oxygen evolution reaction (OER) activity, however, their poor stability in acidic electrolyte remains a critical bottleneck hindering their application in proton exchange membrane water electrolysis (PEMWE). Herein, we construct a RuO 2 ‐based catalyst modified with Ru nanoparticles and grain boundaries (mG‐RuO 2 ) to simultaneously improve OER activity and stability. The resulting mG‐RuO 2 catalyst demonstrates superior acidic OER performance, requiring only 171 mV overpotential to reach 10 mA cm −2 and showing stable operation over 650 h. Theoretical calculations combined with in situ spectral analysis reveal that Ru nanoparticles not only break the H‐bond network of water in the double‐layer structure but also overcome the limitations of the adsorbate evolution mechanism pathway through efficient OH* spillover, thereby simultaneously enhancing the activity and stability of mG‐RuO 2 . Moreover, the grain boundaries increase oxygen vacancies in RuO 2 , thereby suppressing the lattice oxygen mechanism and improving structural stability. More importantly, mG‐RuO 2 requires only 1.556 V to reach 1 A cm −2 , while maintaining outstanding stability for over 500 h under this condition. This work elucidates the special OH* spillover mechanism in acidic OER, shedding light on the rational design of highly active, and stable RuO 2 ‐based electrocatalysts for PEMWE.