Abstract
Transition metal catalysts have attracted attention recently because of their promising oxygen reduction reaction (ORR) activity in fuel cells. In this work, the density functional theory calculations were carried out to explore the stability and ORR mechanism of Ni atom-pair supported by N doped graphene. The results indicate that it is thermodynamically stable due to the negative formation energy. The investigation of adsorption properties of O2 molecular show that O2 would like to adsorb on bridge site between two Ni atoms with charge transfer of 0.68|e|. Based on this configuration, the mechanism of ORR was studied in detail. The calculated results indicate that the ORR undergoes four-electron process on Ni2N6 active sites. The calculations of the free energy diagrams show that three ORR pathways are down-hill, which means the reactions are overall exothermic and the overpotential is predicted to be 0.35 V.
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