Investigation Of Pt-based Alloy Catalysts For Direct Methanol Fuel Cell

The basic structure, the research current status, and key technical problems of direct methanol fuel cell (DMFC) were summarized in this paper. And the development and the preparation methods of anode catalysts were also reviewed. The factors that affect the performance of catalysts prepared by using impregnation reduction method were also introduced.This research is aimed to improve the utilization and activity of anode catalysts for methanol electrooxidation. The direct methanol fuel cell anode catalysts, PtNi/C and PtNiPb/C, were prepared by chemical reduction method. We use the CHI-630A electrochemical analyzer to test electrochemical properties of the catalysts. The particle size, lattice parameter, composition, micro-morphology, and surface states of metals in the PtNi/C and PtNiPb/C surface particles were determined by X-ray diffraction (XRD), energy dispersive analysis of X-ray (EDAX) analysis, transmission electron microscopy (TEM), and X-ray photoelectron spectrometry (XPS), respectively. Their performances of catalysts were tested by using a glassy carbon disk electrode through cyclic voltammetric curves, chronoamperometric curves, and amperometric i-t curves in a solution of 0.5 mol·L^-1 CH₃OH and 0.5 mol·L^-1 H₂SO₄.The results show that PtNi/C catalyst has the best performace with an atomic ratio of Pt: Ni =8:2, 80℃, and pH=8 among different PtNi/C catalysts. XRD analysis shows that the catalysts exhibit face-centered cubic structures and have biger lattice parameters than Pt/C (E-Tek) one. Their sizes are relatively biger, about 4.0 nm. No significant differences in performance were found on both the PtNi/C and Pt/C(E-Tek) catalysts for methanol electrooxidation by using cyclic voltammetry. Their size distribution of the metal nanoparticles is very asymmetry, with evident agglomeration. This is similar to proportion of PtNi comparing with theory from EDAX, There are a lot of NiO, Ni(OH)₂, NiOOH, and Pt in the PtNi/C catalyst from XPS. PtNi/C catalyst has smaller active, lower contents of Pt, while PtNi/C catalyst has a bad long-term stability.Optimal reaction conditions of the PtNiPb/C catalyst is a 5:4:1 of Pt: Ni: Pb, at 90℃, at a pH value of 10. The catalytic activity of the PtNiPb/C catalyst is much higher for methanol electrooxidation than that of the Pt/C (E-Tek) one. Also, its CO-tolerance is better than that of the Pt/C. But it has a lower long-term stability. This is similar to proportion of PtNiPb compareing with theory from EDAX. This are a lot of NiO, Ni(OH)₂, NiOOH, PbO, and Pt in the PtNiPb/C catalyst surface from XPS.Catalysts were heated in the four different temperatures such as 200℃, 250℃, 300℃, 350℃. Its stability of the PtNiPb/C catalyst was improved after heat treatment. The catalyst structure was modified, and there was an increase in the conversion of ruthenium into the alloyed state and an increase of particle size with the increase of heat treatment temperatures.