Asymmetric Charge Redistribution at the Tri‐Functional Cu ₁ –Ru/CeO _<i>x</i> Interface Enables Alkaline Hydrogen Evolution Reaction

ABSTRACT The development of efficient electrocatalysts for the alkaline hydrogen evolution reaction (HER) remains a key challenge for hydrogen energy conversion. Here, we report a Cu‐substituted Ru nanoparticle catalyst in which atomically dispersed Cu (0.31 wt%) is substituted into Ru nanoparticles (3.54 wt%) supported on oxygen‐deficient ceria (Cu 1 –Ru/CeO x ). This catalyst exhibits outstanding alkaline HER performance, delivering a low overpotential of 47 mV at 10 mA cm −2 , a small Tafel slope of 43 mV dec −1 , and a high mass activity exceeding 3.0 , outperforming commercial Pt/C. The catalyst retains 95% of its initial activity after 100 h of continuous operation. Spectroscopic, structural, and DFT analyses reveal an asymmetric interfacial charge distribution: charge transfer from Cu to Ru generates electron‐rich Ru and electron‐deficient Cu 1 , while electron donation from Ru to ceria forms Ce 3+ and oxygen vacancies. This tri‐functional interface enables efficient water dissociation at Ce 3+ –O v sites, optimized hydroxyl adsorption/desorption on electron‐rich Ru, and weakened H binding on electron‐deficient Cu 1 , thereby promoting H 2 release. When paired with a RuO 2 anode, the Cu 1 –Ru/CeO x (−)║RuO 2 (+) electrolyzer surpasses Pt/C(−)║RuO 2 (+) in full‐cell efficiency and long‐term stability, highlighting the importance of interfacial charge modulation and multi‐site cooperativity in alkaline HER catalysis.