The promotion effects of graphitic and pyridinic N combinational doping on graphene for ORR

The promising catalytic activity of nitrogen-doped graphene (N-graphene) for various heterogenous processes has attracted extensive attention, but the active sites of N-graphene for O2 adsorption and the underlying activation mechanism are still unclear. Density functional theory (DFT) was used in this work to investigate the role of graphitic N (GrN), pyridinic N (PyN), and their coexistence in graphene on O2 adsorption and activation. It was found that O2 adsorption is energetically promoted by GrN with the adsorption site atop it. The initially protonated O2 (OOH∗) prefers to bind with the C atom adjacent to the GrN. More interesting, the combinational of PyN and GrN can further redistribute charge among the carbon materials, which subsequently promotes O2 adsorption and lowers the energy barrier of O2 hydrogenation, demonstrating an improved property for ORR. This finding can help to identify the active site of O2 adsorption and protonation on N-graphene and clarify the function of different doped N, providing a guiding suggestion for the experimental design of N-doped graphene.