Density functional theory study of adsorption and diffusion of potassium atoms on zigzag graphene nanoribbons with different terminal groups

Despite the extensive use of graphene-based materials in K-ion batteries, the effects of various edge morphologies of graphene on K atom adsorption and diffusion are unclear. In this study, the effects of K atom adsorption and diffusion on zigzag graphene nanoribbons (ZGNRs) with hydrogen (-H), ketone (=O), hydroxyl (-OH), and carboxyl (-COOH) terminal groups were investigated by density functional theory calculations. ZGNRs terminating with -H, =O and -COOH promote K atom adsorption, whereas those terminating with -OH suppress it. The -H, =O, -OH and -COOH terminations have a negligible effect on K atom diffusion in the inner region of ZGNRs. In the edge region, the diffusion barriers are nearly unchanged for -H and -OH terminations; however, they are increased for =O and -COOH terminations in the edge region compared to those in the inner region. All the terminal groups hinder K atom diffusion from the edge region toward the inner region. Our results suggest that -H termination enhances K atom adsorption and has a negligible effect on the diffusion barrier of K atom in the edge region. Therefore, the ZGNR with -H termination could be a promising candidate for K-ion batteries.