A DFT Study Of Oxygen Reduction Reaction Mechanism Over O-doped Graphene-supported Pt-based Alloy Catalysts

Fuel cells have gained increasing attention in recent years due to their highefficiency for energy conversion, high power density, low operating temperature andabove all, low pollution with renewable fuel sources. Since the oxygen reductionreaction at the cathode is~100times slower than the hydrogen oxidation reaction atthe anode, developing a highly efficient cathode catalyst will have a significant impacton fuel cell applications. A new supported alloy catalyst aiming at reducing theprecious metal loadings has been found to accelerate the activity of oxygen reductionreaction. Meanwhile, the lower cost will speed up the development of fuel cell. Butthe mechanism and kinetics of oxygen reduction to shed light on the enhancementmechanism over supported alloy catalyst is still unclear. A detailed analysis ofmechanism and kinetics will also help to provide effective guidance on oxygenreduction catalyst design.In this dissertation, density functional theory calculations were performed toinvestigate the pathways of oxygen reduction reaction over Pt and Pt-based alloycatalysts supported on O-doped graphene substrate. The results show that the danglingC atom resulting from oxygen doping becomes an anchor site for metal clusters. Ourresults also showed that O2adsorbs as a di-oxygen species on the supported Pt4, Pt3Ti,Pt3Mn, Pt3Fe, Pt3Co and Pt3Ni clusters, but dissociates spontaneously on supportedPt3V and Pt3Cr. All the introduced atoms (Ti, V, Cr, Mn, Fe, Co and Ni) canefficiently promote electron transfer to the oxygen species. The di-oxygen speciesdissociates into co-adsorbed HO*and O*upon reduction on all supported clusters andno stable HOO*intermediates were isolated. On supported Pt4, Pt3Cr and Pt3Co,further reduction via both HO*+HO*and H2O*+O*routes is possible, with reactionfavoring the HO*+HO*route energetically. On supported Pt3Fe, the HO*+HO*andH2O*+O*routes are competitive. On supported Pt3V, the reduction reaction is likelyto 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 theexperimentally observed enhancement of oxygen reduction reaction reactivity ongraphene supported Pt3Cr and Pt3Co nanocatalysts, and achieved expected results.