Tailoring sulfur reactivity in ReS₂ via d–p orbital hybridization for efficient hydrogen production

The intrinsic anisotropy and tunable electronic structure of rhenium disulfide (ReS₂) make it a compelling platform for electrocatalytic hydrogen evolution, yet its activity is hampered by the imbalanced hydrogen adsorption–desorption kinetics at sulfur active sites. Here, we report a rational orbital-level engineering strategy to unlock the electrocatalytic potential of ReS₂ via Co-induced d–p impurity orbital hybridization. Density functional theory calculations reveal that Co-doping introduces localized impurity electronic states and facilitates strong hybridization between Co 3d and S 3p orbitals, establishing a directional charge transfer pathway from S to Co. This interaction depletes the local electron density around surface S atoms, attenuates the S 3p–H 1 s orbital overlap, and lowers the thermodynamic barrier for hydrogen desorption. As a result, the hydrogen adsorption–desorption equilibrium is significantly improved, facilitating rapid turnover and sustained regeneration of sulfur sites. Guided by these theoretical insights, we synthesize a Co-doped ReS₂ catalyst (Co2–ReS₂, ~5 at.% Co), which exhibits markedly enhanced HER performance, achieving a low overpotential of 98 mV at 10 mA cm⁻². More importantly, Co2–ReS₂ demonstrates long-term operational stability exceeding 50 h without measurable degradation, underscoring the robustness of the engineered sulfur active sites. This work demonstrates an effective orbital-level engineering strategy for activating chalcogen sites and offers a versatile framework for designing high-performance electrocatalysts for hydrogen production.