Shaping alkaline hydrogen evolution at Ti-vacancy mediated valence-asymmetric Ru on TiO2 quantum dots

It remains a significant challenge for simultaneously regulating the water dissociation and hydrogen adsorption/desorption of Ru in alkaline media. Herein, we successfully architected an entity of individually-functionalized spatial valence-asymmetric Ru sites on Ru/TiO 2 quantum dots for high-performance alkaline hydrogen evolution. The Ru nanoclusters were self-adaptively grown along the Ti vacancies, triggering the phase transformation from anatase to rutile TiO 2 . The well-defined Ru/TiO 2 interface produced a strong electronic metal-support interaction, acquiring a Ru site with asymmetric electronic state. Resultantly, the anisotropy of the surface low-valence Ru δ- site and the interface high-valence Ru δ+ site break the scaling relationship of water dissociation, hydroxyl and hydrogen adsorption. The asymmetrical Ru electronic state achieves 15 mV overpotential at 10 mA cm -2 and delivers a high mass activity of 5.4-fold than commercial Pt/C at 100 mV, outperforming most reported Ru-based catalysts. Our work sheds light on the potential of support-crystal phase engineering to design catalysts with the required electrocatalytic performance.