Electrocatalytic nitrogen fixation using single-atom catalysts (SACs) offers a promising strategy for the sustainable production of NH3. On the basis of density functional theory, we systematically explored the potential for N2 electroreduction of single-atom catalysts (SACs) covering V, Nb, and Ta transition metal (TM) centers supported by graphene and g-C3N4 substrates. The single Nb-atom embedded on g-C3N4 nanosheet possesses outstanding nitrogen reduction reaction (NRR) catalytic activity and exhibits better performance than graphene with a considerably smaller maximum ΔG value (0.05 eV). The single Nb atom on g-C3N4 with more negative valence provides structural advantages for hosting empty d-orbitals for strong N2 and N2H adsorption, as well as more single d-electrons to further promote back-donation to activate the NN triple bond. This work may be helpful in developing more effective TM-based SACs for N2 reduction through varying substrate effect toward the same single-atom catalysts.

We perform first‐principles calculations to investigate whether or not nitrogen is the best dopant in system of Co−X4 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−X4 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 dz2 orbital as well as the reduced work function are responsible for the unexpected activity of Co‐S4 embedded graphene for HER. Overall, Co‐S4 embedded graphene catalyst could be a good candidate for hydrogen evolution reaction.

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