▎ 摘　　要

We perform first-principles calculations to investigate whether or not nitrogen is the best dopant in system of Co-X-4 embedded graphene (X=N, S, B, and P) electrocatalysts towards hydrogen evolution reaction(HER). Our theoretical results reveal that N, S, B, and P-doped graphene can enhance the catalytic activity toward HER compared with the pristine graphene, and S doped graphene exhibits more favorable performance than N doped graphene, consistent with the experimental results. For the Co-X-4 embedded graphene (X=N, S, B, and P), we predict that S may be a promising dopant in graphene supported single atom Co. The rather low hydrogen adsorption free energy (-0.07 eV) and activation energy barrier (0.78 eV) for the rate-determining step, the downshift of the d band center, the enhanced charge density of d(z)(2) orbital as well as the reduced work function are responsible for the unexpected activity of Co-S-4 embedded graphene for HER. Overall, Co-S-4 embedded graphene catalyst could be a good candidate for hydrogen evolution reaction.