Bias-Responsive S-Scheme Heterojunctions Reconfigure Interfacial Water for Efficient Seawater Hydrogen Evolution.

Electrocatalytic seawater hydrogen evolution is fundamentally limited by the rigidity of interfacial water structures and static electron distributions at catalyst surfaces. Here, we report a bias-responsive S-scheme heterojunction that dynamically couples nonequilibrium electron redistribution with interfacial water activation during operation. Using a MoN/NiCoN model system, in situ x-ray absorption spectroscopy (XAS) reveals a cathodic-bias-induced reversal of interfacial electron transfer relative to the equilibrium state, leading to progressive electron enrichment at the catalytic interface. In situ infrared spectroscopy reveals potential-dependent restructuring of the interfacial water environment associated with this electronic redistribution, transforming strongly and intermediately hydrogen-bonded water into catalytically active free or weakly hydrogen-bonded species. Ab initio molecular dynamics simulations further reveal accelerated hydrogen-bond exchange kinetics, shortened hydrogen-bond lifetimes, and a more adaptive dipole orientation at the MoN/NiCoN interface, providing molecular-level evidence for dynamic water-network reorganization. Ionic-liquid-based experiments further demonstrate that this restructuring originates from electronically driven interfacial activation rather than bulk water availability. Consequently, water dissociation and hydrogen evolution kinetics are synergistically accelerated, enabling ultralow overpotentials in real seawater and high solar-to-hydrogen (STH) conversion efficiency. This work establishes dynamic S-scheme heterojunctions as a general strategy for electronically programmable interfacial reaction environments in electrocatalysis.