| It is well known that Platinum is the most efficient catalyst in the direct methanol fuel cells. However, Platinum is easily poisoned by chemisorption of CO produced by dissociative adsorption of methanol. By far, PtRu bimetallic catalysts are the most acceptable catalysts to tolerate CO. Nevertheless, the ruthenium loss during the anode reaction at working condition is a severe problem, due to the unstablilty and solublility of ruthenium. Pt-Rh catalysts are considered to be the most promising bimetallic anode catalyst candidate. And recent research has mostly focused on the preparation, characterization of rhodium modified platinum single crystals and their applications in electro-oxidation of CO, CH3OH, CH3CH2OH, etc. There have been few papers concerning the formation and characterization of surface alloys, the preparation of actual supported PtRh alloy catalysts.Firstly, the preparation and characterization of PtRh bimetallic film on the Pt mesh with different content of Pt, Rh by force deposition were studied and the effects of the variation of the deposit structure and the catalytic in the methanol electrooxidation were investigated by means of cyclic voltammetry (CV). Then, using graphite as the carrier, Pt5/C substrate was prepared by formaldehyde reduction at ultrasonic enviroument. The effects of different calcination temperature and different reduction temperature to the catalytic properties of Pt5/C were studied. On the Pt5/C substrate, PtxRhy/Pt5/C,PtxRhyPtz/Pt5/C "sandwich structure" layers were deposited by force deposit method. The effects of the variation of the deposit structure, the amount of Pt, Rh and reduction atmosphere on the formation of supported PtRh alloy were studied via CV and X-ray diffraction (XRD), and the methanol catalytic electrooxidation on the surface fo above catalysts were studied as well.The results are as follows:(1) It is observed that both pure Rh and PtRhPt sandwich structure deposit growth are epitaxial on the Pt mesh by force deposition. For pure Rh deposits, there is no siganificant change for the onset potentials of methanol oxidation, but the peak potential of methanol oxidation on the reduced catalysts was 40mV lower than that on the pure Pt mesh, with the Rh coverage increases, the current density of methanol significantly reduced. The PtRhPt sandwich structure deposit on Pt mesh formed partial alloy during the deposition process, which showed better catalytic activity and stability. The peak potential of methanol oxidation at Pt1Rh8Pt1 was 45mV more negative than that on pure Pt mesh, while the oxidation peak current intensity increased by 40%.(2) The self-made Pt5/C substrate possesses similar properties as Pt polycrystal electrode. The calcination temperature has less effect on the catalytic activity of the Pt5/C substrate. The only difference is the current density of methanol oxidation on Pt5/C calcined at 400℃was higher than on those calicned at other ptemoratures.(3) Similar to PtRh alloy formed on Pt mesh, epitaxial PtRh alloy formation are observed on Pt5/C substrate. Therein, PtRh surface alloy derived from Pt0.1Rh2/Pt5/C sandwich structure shows better catalytic activity in methanol electrooxidation, which the oxidation potential was 60mV negative shift compared to that on pure Pt5/C.
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