▎ 摘　　要

Optimizing the hydrogen adsorption Gibbs free energy (Delta G(H)) of active sites is essential to improve the overpotential of the electrocatalytic hydrogen evolution reaction (HER). We doped graphene-like Co0.85Se with sulfur and found that the active sites are reversed (from cationic Co sites to anionic S sites), which contributed to an enhancement in electrocatalytic HER performance. The optimal S-doped Co0.85Se composite has an overpotential of 108 mV (at 10 mA cm(-2)) and a Tafel slope of 59 mV dec(-1), which exceeds other reported Co0.85Se-based electrocatalysts. The doped S sites have much higher activity than the Co sites, with a hydrogen adsorption Gibbs free energy (Delta G(H)) close to zero (0.067 eV), which reduces the reaction barrier for hydrogen production. This work provides inspiration for optimizing the intrinsic HER activity of other related transition metal chalcogenides.