Chlorine Coordination Engineering Optimizes Hydrogen Evolution Reaction Kinetics on Ru(100) Facet

Abstract Electrocatalytic water splitting stands as a pivotal technology for the large‐scale production of high‐purity hydrogen, with the central challenge residing in the development of efficient, stable, and cost‐effective hydrogen evolution reaction (HER) catalysts. This study proposes a simple, room‐temperature stirring method (2 h) developed to anchor [RuCl] 2+ onto carboxyl‐functionalized carbon nanotubes (CNT‐COOH). During the hydrogen evolution reaction (HER), partial Cl⁻ desorption under reductive potentials triggers the in situ formation of Cl‐modified Ru (100) nanoparticles. Localized Cl⁻ coordination induces redistribution of surface electronic states and mitigation site‐blocking effects, activating the traditionally inert (100) facets through optimization of Ru electronic states, thereby surpassing the activity of conventionally synthesized Ru/CNT(101) (prepared via pyrolysis). The self‐optimized Ru/CNT(Cl‐100) demonstrated exceptional mass activity (6.47 A mg Ru ⁻¹ at η = 50 mV) and sustained stability, outperforming most reported Ru‐based catalysts. This work highlights a ligand‐mediated strategy to unlock the latent catalytic potential of low‐index facets, providing a scalable pathway for high‐performance HER systems.