Iron-zinc bimetal embedded N-doped graphene for the oxygen reduction reaction catalysis: A density functional theory study

In this work, the catalytic activity for the oxygen reduction reaction (ORR) of Fe-Zn bimetal embedded N-doped graphene (FeZnN6) is investigated in detail by density functional theory method. The result of formation energy indicates that the FeZnN6 possesses relatively good likelihood of existence compared with the catalyst with the similar structure. Based on the calculated binding energy of the ORR species, it can be found that FeZnN6 exhibits excessive strong binding strength of *O and *OH, indicating its low catalytic activity. However, the binding strength could be effectively tuned after the FeZnN6 is modified by O or OH ligand, namely, FeZnN6(O) and FeZnN6(OH). The modification of ligand not only changes the mechanism of ORR, but also enhances the catalytic activity. The calculated ORR overpotential of FeZnN6(OH) is only 0.37 V, which is smaller than that of Pt(111). Electronic structure analysis reveals that the ligand itself will receive part of electrons from the active site, resulting in less negative charges on the ORR species. Therefore, between catalyst and adsorbed species, the electrostatic interaction and the binding strength are weakened. Besides, the FeZnN6(OH) is predicted to have excellent poisoning-tolerance ability to CO, NO, NH3, SO2, and H2S.