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

Abstract

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.