| Anode electro-catalyst is the most important part of direct methanolfuel cell and platinum is regarded as an ideal anode catalyst. However,the high price, limited resource and low tolerance to CO poisoning limitits application. In order to reduce the Pt content and improve theelectrocatalytic activity of anode electro-catalyst, Pt should be replacedby Au@Pt nanoparticles. Gold nanoparticles with different particle sizehave been synthetized by various methods. The influences oftechnological parameters on the morphology, particle size and dispersionof the synthesized gold nanoparticles are discussed by controlling variatemethod. Using transmission electron microscopy and UV-Visspectroscopy characterizes the gold nanoparticles’ morphology andparticle size distribution. Au@Pt core-shell nanoparticles weresuccessfully synthesized by successive reduction and were thenassembled on Vulcan XC-72carbon surface (noted as Au@Pt/C). Themorphology and distribution of Au@Pt nanoparticles were characterizedby UV-Vis spectroscopy, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectronspectroscopy (XPS) and the corresponding result is that core-shell likestructure is observed. The Au@Pt/C catalysts with different Au/Pt atomicratios were characterized by TEM, X-ray diffraction (XRD), and X-rayphotoelectron spectroscopy (XPS). The electrocatalytic activities ofAu@Pt/C catalysts were investigated by cyclic voltammetry (CV). Themain conclusions are as follows:(1) The optimized processing parameters for preparing goldnanoparticles with an average diameter of4.3nm were worked out, themolar ratio of chloroauric acid and NaBH4is3.75:1; the mass ratio ofPVP and chloroauric acid is1:1; the reaction temperature is100℃; theNaBH4is added after chloroauric acid.(2) Using sodium citrate as both reducing agent and protective agent,the optimized processing parameters for preparing gold nanoparticleswith an average diameter of13.8nm were worked out, the molar ratio ofchloroauric acid and sodium citrate is1:4.5, the reaction temperature is100℃; sodium citrate is added before chloroauric acid.(3) Gold nanoparticles with an average diameter bigger than20nmwere synthesized by seeded growth method. Ascorbic acid and Na2SO3,which are weak reductive performed better than NaBH4, especially wasascorbic acid. With the molar ratio of chloroauric acid and gold seedchanging from8:1,6:1,4:1to2:1, the particle diameter of the prepared gold nanoparticles have gradually decreased, while the particle sizedistribution have diminished and then became bigger. The optimizedprocessing parameter was that the molar ratio of chloroauric acid andgold seed is4:1.(4) Gold colloid with an average diameter of13.8nm was used asseed, then core-shell Au@Pt nanoparticles were prepared by the seededgrowth method. Chloroplatinic acid could be reduced by ascorbic acidwhen the malor ratio of ascorbic acid and chloroplatinic acid was4:1.Vulcan XC-72which was preprocessed by heating in N2acted as supportmaterials better than Vulcan XC-72without any pretreatment. Thecatalytic activity of the core-shell catalyst for MOR decreases in the order:Au@Pt/C(1:2), Au@Pt/C(1:1), Au@Pt/C(1:4), Au@Pt/C(2:1), Pt/C,Au/C. The better catalytic activity of Au@Pt/C(1:2) results from its betterresistance to toxic CO than Pt/C. Further more, Au@Pt/C(1:2) catalystshows good long-term cycle stability and91.1%value of peak current ofmethanol oxidation remains after200cycles. The consumption ofmethanol during the successive scans results in the decrease of theelectrocatalytic activity. |
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