The mechanism study of oxygen reduction reaction (ORR) on non-equivalent P, N co-doped graphene

The density functional theory (DFT) calculations in this study were applied to investigate the oxygen reduction reaction (ORR) mechanism of non-equivalent P, N co-doped graphene. The simulation results showed that the formation of sp(3) hybridization was energetically more profitable than that of the sp(3)d hybridized doped form. O-2 molecules directly dissociated on G-PN2C1 and G-PN3 by following the Eley-Rideal (ER) mechanism, which involves H2O formation by reaction with H+ from the electrolyte. Furthermore, G-PN3 was found to perform better as ORR catalysts in an acidic medium due to their low overpotentials of 0.419 V. In contrast, G-PN3C1 and G-PN4 tended to follow the OOH* formation pathway, which showed a higher overpotential for the ORR. X-ray photoelectron spectroscopy (XPS) analysis and electrochemical experiments were performed to verify the calculation results, which indicated that the appropriate proportions of G-PN 3 led to greatly improved ORR per- formance in the following order: G-N < < G-P1N1.5 < G-P1N2.9. Therefore, enhanced catalytic performance for the ORR in an acidic medium can be achieved by controlling the proportions of N and P in the P, N co-doped graphene, so that we can design an efficient non-metallic catalyst for the cathode of proton-exchange membrane fuel cells.