Single-atom doped graphene for hydrogen evolution reactions

Atomic doping is a widely used technique to modify the electronic properties of two-dimensional materials for various applications. In this study, we investigate the catalytic properties of single-atom doped graphene as electrocatalysts for hydrogen evolution reactions (HERs) using first-principles calculations. We consider several elements, including Al, Ga, In, Si, Ge, Sn, P, As, and Sb, which were interstitially doped into single and double C vacancies in graphene. Our density functional theory calculations show that all the considered doped graphene, except for As-doped graphene, can be highly active for HER, with hydrogen adsorption free energies (Delta G (H*)) close to the optimal value (Delta G (H*) = 0), ranging from -0.19 to 0.11 eV. Specifically, Delta G (H*) of Al, Ga, In, and Ge are much closer to zero when doped in the single vacancy than in the double vacancy. In contrast, Delta G (H*) of Sb and Sn are much closer to zero in the double vacancy. Si and P have Delta G (H*) values close to the optimum in both vacancies. Interestingly, the vacancy numbers play a crucial role in forming orbital hybridizations, resulting in distinct electronic distributions for most dopants. As a result, a few doped graphenes show distinctive ferrimagnetic and ferromagnetic orders, which is also an important factor for determining the strength of H adsorption. These findings have important implications for designing graphene-based HER catalysis.