First-principles study of adsorption and migration of alkali and alkaline earth metals (Rb, Cs, and Ba) on graphene

Abstract

The adsorption and migration characteristics of Rb, Cs, and Ba on pristine and defective graphene have been systematically investigated by utilizing the density functional theory (DFT) method, which could help address the challenges of developing novel anode materials of thermionic energy converters (TECs). In this work, we found that the work function of the adsorption system is lower as Cs is adsorbed on graphene compared with Rb and Ba, which indicates that the electron emission capability has been greatly improved. Computational results of defective graphene demonstrate that defect sites act as traps for metals. The diffusion near the Stone-Wales defect and vacancy is severely hindered and the migration barrier on the surface of B/O doped graphene is also slightly increased. Particularly, the work functions of all defective graphenes are significantly increased, which is attributed to the decrease in the probability of electric dipole formation and the increase of the absolute cohesive energy. O-containing defects are ubiquitous in graphene due to their low formation energies, and the lowest work function of defective graphene is 2.74 eV, which is reached after Cs adsorption at 2OC defect sites, whereas this is still expected to have detrimental effects on graphene-based anode materials.