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PaperReview,李俊乾化学工程（专）14102932,Synthesis,characterizationandelectrochemicalstudiesofnano-structuredCaWO4asplatinumsupportforoxygenreductionreaction(纳米钨酸钙的合成、表征和其负载铂对氧还原反应的电催化),1,Literaturesource,2,Contents,Introduction,1,2,Experimentalsection,1,Conclusions,2,3,4,Resultsanddiscussion,3,1.Introduction,Inrecentyears,protonexchangemembranefuelcells(PEMFCs)havebeenrecognizedaspromisingdevicesforportableandtransportapplicationsduetotheirgoodenergyconversionefficiency,highpowerdensity,lowoperatingtemperature,andeasytransport.,PEMFCSworkingprinciple:,4,1.Introduction,Thecathodicreactionofoxygenreductionreaction(ORR),Theanodicreactionofhydrogenoxidationreactionfor,H2+2M2MH2MH2M+2H+2e-,O2+H+M+e-MHO2MHO2+H+e-MO+H2OMO+H+e-MOHMOH+H+e-M+H2O,Electrocatalyticreactionmechanism:,5,Inthefuelcellintheworkprocess,theplatinumcatalystactivesurfaceareawillbegraduallyreduced,resultingintheattenuationoffuelcellperformance.,thepropertiesofPt/PtMalloyrecessionschematicdiagram,6,Experimentalsection,2,7,2.Experimentalsection,SynthesisofnanostructuredCaWO4:,80C,pH=7,whiteprecipitateswerecollectedbycentrifugation,Na2WO42H2O(5mM),CaCl26H2O(5mM),CaWO4,mixedtogether,driedinitiallyatroomtemperature,calcinate,500Cfor5h,8,2.Experimentalsection,Catalystpreparation:,calciumtungstate(1),Graphite(2),CaWO4/graphiteelectrode,K2PtCl4（2.5mM）,H2SO4（0.25M）,thecatalystofPt/CaWO4-graphite,30wt.%ofn-eicosane,heated,electrochemicallyprecipitated,9,2,3,Resultsanddiscussion,10,3.Resultsanddiscussion,TheapproximatecrystallitesizesofsampleswereestimatedbytheScherrersformula:,TheparticlesizeandmorphologyofCaWO4wereexaminedusingTEM，D=1025nm.,11,3.Resultsanddiscussion,ThesereductionpeaksarenotsymmetricbecauseofdepletionofPtCl42-ionsinthevicinityoftheelectrodesinpotentialsmorenegativethanthepeakpotentials.,CyclicvoltammogramsduringelectrodepositionPtonbothgraphiteandnano-CaWO4/graphite.,12,3.Resultsanddiscussion,(a)and(b)ScanningelectronmicroscopyimagesofPt/CaWO4-graphite.,Inthesepictures,brighterareascorrespondedtoPtandCaWO4thattheplatinumparticlesaredispersedoverthesurfaceofthesupportandgraphitesheet.,13,3.Resultsanddiscussion,(d)TheEDXspectrum,presenceofPt,CaandWinthePt/CaWO4-graphitecatalysts,14,3.Resultsanddiscussion,Areaindicatingthatelectrochemicalactivity.,CyclicvoltammogramsofCaWO4-graphite,graphite,Pt/CaWO4-graphiteandPt/graphiteina0.5MH2SO4aqueoussolutionatscanrateof50mV/s.,ThesizeoftheoxidationandreductioncurrentdependsonthevalueofPt-dispersion.,15,3.Resultsanddiscussion,返回,Theoxygenreductionpeakcurrentincreaseslinearlywiththesquarerootofscanrate,emphasizingonthecontrollingofthereactionbyoxygendiffusiontotheelectrodesurface,CyclicvoltammogramsofthePt/CaWO4-graphiteina0.5MH2SO4atvariousscanrates.,16,3.Resultsanddiscussion,Themorepositivehalfwavepotentialindicatestheenhancedelectroc-atalyticactivityofthecatalystsforORR.,LinearsweepingvoltammogramsofPt/CaWO4-graphiteandPt/graphiteinO2saturated0.5MH2SO4solutionwithascanrateof25mV/s.,17,3.Resultsanddiscussion,ItisclearthatthePt/CaWO4-graphiteshowsalowercharge-transferresistanceduetothesmallersemicirclesdiametercomparedtoPt/graphitecatalystin0.5MH2SO4solution.,NyquistplotforPt/CaWO4-graphiteandPt/graphitein0.5MH2SO4vs.Ag/AgCl.,18,Conclusions,4,19,4.conclusions,Nano-structuredcalciumtungstatewassynthesizedbytheco-precipitation.,TheapplicationofCaWO4asacataly