Pt/AuNiFe/C Multi-metallic Catalysts For Oxygen Reduction Reaction Of Fuel Cells

The synthesis of low cost and highly efficient catalysts for the oxygen reductionreaction (ORR) is one of the urgent needs in the development of fuel cell devices forpractical applications. In recent pioneer studies, it has been demonstrated thatmultimetallic catalysts show superior catalytic properties, which are not attainable bytheir monometallic counterparts, providing attractive perspectives for the effectivetuning of the catalytic performance in proton-exchange membrance fuel cells. Thesuperior catalytic properties are ascribed to the electronic (ligand) effects or geometriceffects (or both) caused by the surface atomic environment of distinct metal atoms. Inthis thesis, we prepared Pt/AuNiFe/C catalysts for the oxygen reduction reaction withthree methods. The main contents and results are summarized as follows:1. Pt/AuNiFe/C catalysts prepared by UPD-RRRPt/AuNiFe/C catalysts were prepared by Cu under potential deposition (Cu UPD)on AuNiFe/C NPs and redox replacement reaction (RRR). A series of Ptn/AuNiFe/Ccatalysts with spiny-cactus-like morphology (where n=the number of Cu-UPD-RRRcycles) were synthesized and their electrochemical properties for ORR wereinvestigated. It is shown that with increased Cu-UPD-RRR cycles, the Ptn/AuNiFe/Ccatalysts show larger electrochemical surface areas and higher ORR activity. But theORR activity for the Ptn/AuNiFe/C catalysts is still very low compared with commercialPt/C catalysts.2. Pt/AuNiFe/C catalysts prepared by RRRCore-shell structured Pt/AuNiFe/C catalysts were prepared by the RRR betweenAuNiFe/C nanoparticles (NPs) and PtCl42-ions in aqueous solution. The surfacemorphology and electrochemical properties for ORR were investigated. It is shown thatthe size of AuNiFe/C NPs is~40nm. After reaction with PtCl42-ions, we found that PtNPs not only exist on the surface of AuNiFe/C, a large number of small and highlydispersed Pt NPs on carbon supports were also observed. The electrochemical activesurface area (ECSA) for the Pt/AuNiFe/C catalysts is1.7times higher than that ofJM-Pt/C catalyst. And Pt-mass activity for the Pt/AuNiFe/C catalysts is1.3times higherthan that of JM-Pt/C catalyst. After5000cycles of sweeping between0.6and1.1V, theECSA of Pt/AuNiFe/C catalysts decreased approximately55.5%, and the half-wave ofPt/AuNiFe/C catalysts decreased approximately15mV. After10000cycles, the ECSA decreased approximately56%, and the half-wave decreased approximately19mV.3. PtAuNiFe/C catalysts prepared by chemical reduction-RRRFirst, AuNiFe NPs were prepared by chemical reduction. Then we can transform afraction of exposed Ni、Fe atoms to Pt by RRR to prepare core-shell structuredPtAuNiFe NPs. Finally, the as-synthesized PtAuNiFe NPs were supported on carbonblack, thus we can get PtAuNiFe/C catalysts. It is shown that the NiFe NPs are inspherical shape and have an average crystallite size of40nm, the AuNiFe NPs are alsoin spherical shape and have an average crystallite size of20nm, and the mean diameterof PtAuNiFe NPs can be as low as≈1.8nm. Further more the PtAuNiFe NPs arewell-dispersed and have a high uniformity in diameter. The ECSAs for thesePtAuNiFe/C-1and PtAuNiFe/C-2catalysts are2.2and2.6times higher than that ofJM-Pt/C catalyst, respectively. And Pt-mass activitives for these PtAuNiFe/C-1andPtAuNiFe/C-2catalysts are2.2and2.8times higher than that of JM-Pt/C catalyst,respectively. After1500cycles of sweeping between0and1.2V, the ECSA ofPtAuNiFe/C-1catalysts decreased approximately77%, and the half-wave decreasedapproximately40mV. After1500cycles, the ECSA of PtAuNiFe/C-2catalystsdecreased approximately72.7%, and the half-wave decreased approximately20mV.