N-Doped Graphene Supported on Metal-Iron Carbide as a Catalyst for the Oxygen Reduction Reaction: Density Functional Theory Study

The development of an efficient electrocatalyst for the oxygen reduction reaction (ORR) is essential for the commercialization of fuel-cell technologies. Iron carbide encapsulated in N-doped graphene (NG/Fe3C) has been recognized recently as a promising ORR catalyst. In this study, the stability and catalytic activity of N-doped graphene supported on metal-iron carbide (NG/M_Fe3C) toward the ORR are investigated by using DFT calculations. The NG/M_Fe3C heterostructure is modeled by substituting Fe atoms in the Fe3C substrate near the NG/Fe3C interface by metal atoms M (M=Cr-Mn, Co-Zn, Nb-Mo, Ta-W). The calculations show that the introduction of the metal atoms M alters the work function of the overlayer N-doped graphene, which is found to correlate with the binding strength of the ORR intermediates. The introduction of Ni or Co atoms at the interface improves the ORR activity of the NG/Fe3C and stabilizes the heterostructure. The ORR activity increases as the concentration of Ni or Co atoms near the interface increases, and the stable heterostructure is available in a wide range of substituted concentrations. These results suggest approaches to improve the ORR activity of NG/Fe3C catalysts.