Interfacial Water Reorientation in Gadolinium‐Doped Ru/RuO <i> _x </i> Heterostructures Boosts Alkaline Hydrogen Oxidation Electrocatalysis

ABSTRACT The sluggish proton transfer in alkaline electrolytes severely limits hydrogen oxidation reaction (HOR) kinetics of fuel cells. Although the orientation of interfacial water strongly governs proton transport, precise control over its configuration remains challenging due to the inherently random distribution of water molecules. Herein, we report the synthesis of isolated Gadolinium (Gd) embedded into Ru/RuO x heterostructures and engineer the built‐in electric fields (BIEF) at the heterostructure for effectively tuning surface oxophilicity and directing the reorientation of interfacial water configuration to boost HOR catalysis of fuel cells. We find that isolated Gd atoms intensify the BIEF at the Ru/RuO x interface, driving strengthened asymmetrical charge redistribution and finely tune work function of catalyst. This electronic modulation in turn optimizes surface oxophilicity of active sites, enabling balanced hydroxyl species coverage and preferential stabilization of H 2 O ↓ ‐oriented water, thereby strengthening hydrogen‐bond network and constructing an efficient interfacial proton‐conduction channel. The resulting Ru/RuO x ‐Gd@C delivers an exceptional mass activity of 8.87 mA µg Ru − 1 and an exchange current density of 0.39 mA cm −2 , outperforming Pt/C by 6.6 and 2.0 times, respectively. An anion‐exchange‐membrane fuel‐cell assembled with Ru/RuO x ‐Gd@C achieves a PGM‐normalized peak power density of 16.3 W mg Ru −1 and operates stably for over 60 h at 0.2 A cm −2 .