A DFT Study of the Oxygen Reduction Reaction Mechanism over the O-Doped Graphene-Supported Pt4/Pt3Fe and Pt3V Alloy Catalysts

Developing a highly efficient ORR catalyst will have a significant impact on fuel cell applications. The graphene supported Pt₃M alloy nanoparticles as ORR catalysts exhibit 3-4 times higher ORR activity than that of the supported Pt catalyst. Here density functional theory calculations were performed to investigate the pathways of the oxygen reduction reaction over the Pt₄ and Pt₃M (M = Fe, V) clusters supported on the O-doped graphene substrate. The results show that the dangling C atom resulting from oxygen doping becomes an anchor site for metal clusters. Our results also showed that O₂ adsorbs as a di-oxygen species on the supported Pt₄ and Pt₃Fe clusters, but dissociates spontaneously on supported Pt₃V. The di-oxygen species dissociates into co-adsorbed HO* and O* upon reduction on both supported Pt₄ and Pt₃Fe and no stable HOO* intermediates were isolated. On supported Pt₄, further reduction via both HO*+HO* and H₂O+O* routes is possible, with reaction favoring the HO*+HO* route energetically. On supported Pt₃Fe, the HO*+HO* and H₂O+O* routes are competitive. On supported Pt₃V, the reduction reaction is likely to proceed exclusively through the HO* + HO* route as no stable co-adsorbed H₂O and O* state was isolated. The results were discussed in the context of the experimentally observed enhancement of ORR reactivity on the graphene supported Pt₃Cr and Pt₃Co nanocatalysts.