Composition-invariant strain engineering of metal sulfides for efficient hydrogen evolution

Lattice strain engineering offers an effective route to regulate the electronic structures of transition-metal sulfides (TMSs) and enhance their catalytic kinetics, yet the intrinsic relationship between strain and activity remains elusive because most strain-inducing methods alter chemical composition. Here, we develop a molten-salt-mediated quenching (MMQ) strategy that enables precise and composition-invariant control of lattice strain in TMSs. Exploiting the thermal-expansion mismatch between TMSs and nitrogen/sulfur co-doped graphene (NSG), tensile strain is introduced during rapid quenching without changing stoichiometry. Conversely, a slow quenching rate enables the full relaxation of thermal stress, thus producing the TMSs without strain. The investigation shows that a faster quenching rate induces a larger tensile strain. By tuning the quenching rate, RuS₂/NSG catalysts with five continuous strain levels (0–6.8%) are synthesized, where the 2.8% strained sample delivers an overpotential of only 24 mV at 10 mA cm⁻² for the hydrogen evolution reaction in alkaline seawater. The corresponding anion-exchange-membrane water electrolyzer maintains stable operation for over 500 h at a large current density of 1 A cm⁻². Mechanistic analyses reveal that moderate strain strengthens Ru–S electronic coupling, elevates Ru d-band center, and optimizes *H adsorption and water-activation energetics. This MMQ concept provides a general approach to isolate and harness pure strain effects for advanced electrocatalyst design.