Density functional theory study of the oxygen reduction reaction mechanism in a BN co-doped graphene electrocatalyst

摘要

Density functional theory calculations were performed to explore the stability and chemistry of active sites, and the mechanism of the ORR in a metal free BN co-doped graphene electrocatalyst. The results show that formation of graphitic G-BC_xN_y defects is energetically favorable than vacancy induced V-BC_xN_y defects in graphene. We find O2 physisorption on G-BC3, G-BC2N and G-BCN2 defects. Thus these defects are unlikely sites that initiate the ORR. In contrast, the chemisorption of ORR species O2, OOH and O, and the downhill energy landscape of the ORR on G-BN3 sites show that G-BN3 sites are active for the complete 4e~- reduction of O2 to 2H2O. We furthermore explore the catalytic activity of vacancy induced V-BC_xN_y defects for the ORR. Much stronger adsorption of O2 and OH on V-BC_xN_y sites compared to G-BN3 sites indicates that V-BC_xN_y sites would likely be blocked by OH and the catalytic activity is limited to G-BN3 sites. Thus, an enhancement in catalytic activity and selectivity of BN co-doped graphene for a net 4e~- complete O2 reduction can be achieved by increasing the concentration of G-BN3 defects.