Reversed active sites boost the intrinsic activity of graphene‐like cobalt selenide for hydrogen evolution

Optimizing hydrogen adsorption Gibbs free energy (ΔG H ) of active sites is essential to improve the overpotential of electrocatalytic hydrogen evolution reaction (HER). Here, we doped S to graphene-like Co 0.85 Se and found that the active sites are reversed (from cationic Co sites to anionic S sites), which contributes to the enhanced electrocatalytic HER performance. The optimal S-doped Co 0.85 Se has the overpotential of 108 mV (at 10 mA/cm 2 ) and Tafel slope of 59 mV/dec, which exceeds other reported Co 0.85 Se-based electrocatalysts. The doped S sites have much higher activity than the Co sites, with hydrogen adsorption Gibbs free energy (ΔG H ) closing 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.