Adsorption of Na on intrinsic, B-doped, N-doped and vacancy graphenes: A first-principles study

We investigate the adsorption of Na atoms on intrinsic graphene and three types of doped graphenes using the first-principles method of density functional theory combined with the pseudopotential approximation. The results indicate that three types of graphenes, i.e. doped with B and N to replace C atoms, and with vacancies by removing C atoms, exhibit prodigious differences from the intrinsic graphene in terms of the adsorption energy, electronic structure and Na storage capacity on graphene. The adsorption energies of Na on B-doped and vacancy graphenes are -1.93 eV and -2.46 eV, respectively, which are about 2.7 times and 3.4 times that of Na on the intrinsic graphene -0.71 eV, while the adsorption energy of Na on N-doped graphene is only -0.27 eV. The orbital hybridizations can be observed in the B-doped and vacancy graphenes, while there is no obvious orbital hybridization in the N-doped graphene as well as the intrinsic graphene. Each B and each vacancy in the graphene could adsorb up to three and five Na atoms, respectively. The Na storage capacity of intrinsic graphene is weak, while that of N-doped graphene is weaker. B-doped and vacancy graphenes are expected to be novel materials for storing Na atoms.