We employed density functional theory (DFT) to investigate the mechanisms of sodium adsorption and diffusion on N-doped graphene nanoribbons (GNR). The calculated adsorption energy of edge region (-1.096 eV) on pristine GNR was stronger than that of center region (-0.836 eV). In addition, the adsorption energies on GNRs with nitrogen-doped defects (4ND, 3NV and pyrrolic: -3.794 ~ -1.837 eV) were stronger than that for the pristine-GNR edge (-1.096 eV). The adsorption of sodium on GNRs were strongly affected by the introduction of nitrogen defects. According to the band structure analysis, 3s
valance orbital of sodium is raised when sodium is adsorbed on GNRs. Moreover, when sodium is adsorbed near nitrogen atoms, the p
orbital of nitrogen is shifted down due to strong interaction between sodium and adjacent nitrogen. Although the adsorption of sodium on GNR with nitrogen-doped defects was improved, the diffusion energy barriers of sodium on the pyrrolic-GNR (0.009 ~ 0.021 eV) was lower than that for the pristine-GNR (0.019 ~ 0.079 eV).
Acknowledgements: This research was supported by Global Frontier Program through the Global Frontier Hybrid Interface Materials (GFHIM) of the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (No. 2013M3A6B1078882 and 2013M3A6B1078874). This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (2014R1A1A1004096).