Sulfur-induced electronic optimization of Mo₅N₆ for hydrogen evolution through topochemical substitution

Nitrogen-rich transition metal nitrides (e.g., Mo₅N₆) have emerged as promising catalysts for the hydrogen evolution reaction (HER) owing to their unique electronic properties and structural stability. However, the higher valence of metal atoms with strong hydrogen adsorption blocks the subsequent desorption process, leading to unsatisfactory HER activity. In this study, we devise a topochemical route for the synthesis of sulfur-doped Mo₅N₆ through the controlled ammoniation of MoS₂. Experiments and density functional theory simulations reveal that the sulfur dopants reform the localized configurations of Mo₅N₆, thereby inducing the electron redistribution and optimizing the hydrogen adsorption energy on the basal plane. Consequently, extraordinary HER performance with an overpotential of 56 mV at 10 mA cm⁻² and a Tafel slope of 37.9 mV dec^-1 are achieved, outperforming most reported Mo nitride-based electrocatalysts. This work provides a feasible strategy to explore efficient electrocatalysts by electronic structure refinement using heteroatom dopants.