Study On Preparation And Performance Of Pt/WO₃-C Catalysts For Proton Exchange Membrane Fuel Cells

The proton exchange membrane fuel cell (PEMFC) is generally considered to bea good candidate for future energy-generating devices. Electrocatalyst is one of theprimary materials in PEMFC. Catalyst activity, stability and cost are significanthurdles to development and commercialization of PEMFCs. In this paper, tungstentrioxide (WO3) was used as alternative catalyst supports, and Pt/WO3-C catalystswere prepared by microwave-assisted polyol process. The influence of preparingconditions, composition and structure of Pt/WO3-C catalysts on the catalytic activityand stability were studied.Pt nanoparticles catalysts with different mean sizes supported on the VulcanXC-72carbon black were synthesized using microwave-assisted polyol process byadjusting different reaction solution pH values. The effect of different reactionsolution pH values on particle size, distribution and catalytic activity of Ptnanoparticles was discussed. The stability of Pt/C catalysts during the acceleratedpotential cycling test and single cell life test was studied. The results show that themean size of Pt nanoparticles is2.80nm at the solution pH value of9, and disperseevenly on carbon black support. The electrocatalytic activity of self-made Pt/Ccatalysts is comparable to that of commercial Pt/C from John Matthey.The WO3-C hybrid materials were prepared by chemical precipitation reaction ofhydrochloric and sodium tungstate in carbon suspension. And then Pt nanoparticleswere deposited by microwave-assisted polyol process on WO3-C. Influences on thecatalytic activity for oxygen reduction and the single proton exchange membrane fuelcell performance were analyzed systematically, such as different contents of WO3andheat treatment temperature of Pt/WO3-C in N2atmosphere. X-ray diffraction (XRD),transmission electron microscope (TEM) and energy dispersion spectrometry (EDS)were used to characterize the Pt/WO3-C catalysts. The results show that the optimumcontent of WO3is10wt%, and heat treatment temperature in N2flow is250℃. WO3presents as monoclinic phase and about2.77nm Pt metal crystallites disperse onWO3-C. Cyclic votammerty and polarization curves of single cells were investigatedto measure the electrocatalytic activity. The synergistic catalytic effect is foundbetween Pt and WO3. The Pt/WO3-C catalysts are more active for oxygen reduction than traditional Pt/C. The accelerated potential cycling test and single cell life testindicate that the Pt/WO3-C catalysts possess substantially enhanced stability incomparison with Pt/C catalysts.Highly active Pt/WO3-C catalysts were synthesized by microwave-assistedpolyol process. Carbon riveted Pt/WO3-C catalysts with a novel structure based on insitu carbonization of the glucose were designed and prepared. The effect of differentamount of coating carbon on electrocatalytic activity of Pt/WO3-C catalysts wasdiscussed. The mean size of Pt nanoparticles of the carbon riveted Pt/WO3-C catalystsis3.02nm when the mass ratio of Pt and glucose is1:1. And its electrochemical activespecific surface area (ESA) reaches as high as83.70m2/g. The accelerated potentialcycling test and single cell life test indicate that the ESA of the carbon rivetedPt/WO3-C catalysts decreases by26.12%, and the maximum power density reduces2.00%. However, the ESA and the maximum power density of the as-preparedPt/WO3-C catalysts decreases by42.71%and4.31%respectively after the same tests,showing that the carbon riveted Pt/WO3-C catalysts have much higher stability.