| Fuels cells, due to its high energy conversion efficiency, high energy density andenvironmentally friendly, is viewed as one of the best energy conversion technologies.However their high cost due to the usage of precious Pt，as well as the poor durability of thePt catalyst, have been major hindrances to the large-scale application of fuel cells, eventhough they are widely recognized as being among the most promising candidates for the nextgeneration of clean-power sources for electrical vehicles and other novel applications.Recently, breakthroughs in generating core-shell structured catalysts may shed some light onfurthering the commercial application of fuel cells, by depositing a monolayer or a very thinlayer of Pt on a relatively cheap core metal nanoparticle, it can result in a type of highperformance core-shell catalyst with high dispersion of Pt, large active surface area, and highutilization of the precious Pt metal. Investigation for core-shell structured catalyst has beenbecoming one of the hottest topics in fuel cell field.In this dissertation work, a series of catalysts, with the high performance, low platinum,good chemical stability and electrochemical stability for goal, were designed and prepared.The performances of the catalysts used for the anode and cathode of low temperature fuelcells were investigated intensively.Firstly, the core-shell structured Ru@Pt/C catalyst with low Pt loading and high activitywas prepared by a pulse electrodeposition approach. In the first stage, we synthesized Ru/Cnanoparticles ((30wt.%of Ru loading, ca.2nm) by an organic colloid method in autoclave.In the second stage, Pt was deposited on the Ru/C nanoparticles through a pulseelectrodeposition process in the electrolyte solution which contains0.5M Pt (NH3)4Cl2/H2O,0.1M Na2SO4and1.25M sodium citrate. The catalyst shows4times higher mass activitytowards the anodic oxidation of methanol and3times higher mass activity towards thecathodic reduction of oxygen than those of commercial Pt/C catalyst.Secondly, we prepared the Ir@Pt/C catalyst (ca.4nm) by depositing Pt layer on the Ir/Cnanoparticles (30wt.%of Ir loading, ca.1.6nm) using pulse electrodeposition method. Forcomparison, we also prepared a PtIr/C alloy catalyst by a impregnation method. The electrochemical performance of Ir@Pt/C catalyst, PtIr/C alloy catalyst and commercial Pt/Ccatalyst (JM-Pt/C) were studied. Ir@Pt/C catalyst (101.42m2/g Pt) exhibited over3timeshigher mass activity towards the anodic oxidation of methanol than that of JM-Pt/C catalystand over2times higher than that of alloy PtIr/C catalyst, also exhibited over3times highermass activity towards the cathodic reduction of oxygen than that of JM-Pt/C catalyst and over7times higher than that of alloy PtIr/C catalyst.Thirdly, a series of RuIr/C alloy nanoparticles with different Ir/Ru ratio (30wt.%of totalmetal loading) were prepared by a impregnation method. RuIr/C was followed by depositingPt layer on the RuIr/C nanoparticles using pulse electrodeposition to obtain RuIr@Pt/Ccatalysts. We studied the performance on HUPD, MOR, ORR and CO stripping and foundthat the catalyst got the best electrocatalytic property when Ir/Ru ratio was9/1.Finally, we applied pulse electrodeposition method to synthesize kinds of core-shellstructured catalysts (M@Pt/C) from M/C (M=Ru, Ir, Au, Pd;30wt.%of M loading), whichwas at the similar size and prepared by different methods. We compared the electrocatalyticactivity of these catalysts, and got the best results of MOR and ORR when using Ir as the corenanoparticles; while the Au@Pt/C got the worst. |
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