Transition metal-Nx doped graphene as an efficient oxygen reduction reaction catalyst: A theoretical perspective

Currently, single atomic catalysts have been extensively explored as electrocatalysts for the oxygen reduction reaction (ORR) for several important energy conversion technologies. We systematically evaluated the catalytic activities of transition metal (Tm) coordinated with N atoms in graphene (TmNx-gra) towards ORR. A series of metals comprising 3d (Fe similar to Ni), 4d (Ru similar to Pd) and 5d (Os similar to Pt) have been employed and systematically investigated their formation energies, bonding energies, adsorption energies of the reaction intermediates and stability characteristics by density functional theory (DFT). The Fukui functional analysis revealed that the Tm atom as active site of TmN4-gra. Excluding OsN4-gra, Eads-OOH and Eads-OH of TmN4-gra have obvious linear relationship: E-a(ds)-OOH approximate to Eads-OH + 1. Based on the requirements of relatively stable adsorption of ORR intermediates (O-2, O, OH, OOH) and low overpotentials, the theoretical study forecasts that CoN4-gra, RhN4-gra and IrN4-gra are the promising ORR catalysts with the overpotentials are 0.448 V, 0.362 V and 0.339 V, respectively.