Interface Switchable Bonding Tailored Ruthenium Sites Unveil Ultralow Overpotentials for Hydrogen Evolution

Controlling the electronic structure based on the valence state is key for effective electrocatalysis, and the challenge lies in attaining the optimal metal valence states. Here, a new approach called valence‐elastic control is introduced to create intermediate‐valence Ru species within a‐RuO x /C catalyst matrices. By utilizing hetero‐interfaces between RuO x and C, pathways for efficient electron transfer and precise valence adjustment are activated through switchable bonding at the interfaces. The catalyst demonstrates exceptional performance in hydrogen evolution reaction with an unprecedentedly low overpotential of 4.1 mV in KOH + seawater electrolytes at 10 mA cm −2 . Furthermore, the two‐electrode electrolyzer demonstrates improved stability and voltage efficiency compared to the commercial Pt/C‐based system. The in situ tests combined with theoretical analysis reveal the water dissociation and *H adsorption are optimized by the switchable interface bonding of the tailored Ru species. This study showcases a transformative design framework for next‐generation high‐efficiency metal catalysts with variable valence.