（青岛大学浮山校区山东青岛266071）
ABSTRACT：Protonexchangemembranefuelcells(PEMFC)arepromisinginenergyefficiency,highenergydensity,noliquidelectrolytecorrosion,lowtemperaturequickstarting,compactingstructurewhichmadeithasawideapplicationprospectinelectricvehicles,underwatersubmarineandcommunicationpower.Thispaperismainlyreviewedthetheworkingprincipleoftheprotonexchangemembranefuelcell.Thetestmethodofdurabilityandthedegradationmechanismareanalyzed.MoreresearchneedstobedonetostudythedurabilityofPEMFC.
Keywords:protonexchangemembranefuelcells;durability;degradationmech
1Introdutcion
TheProtonexchangemembranefuelcell(PEMFC)isconsideredasanenvironmentallyfriendlypowergenerationdevice.Comparedwithsomeconventionalpowderdevices,ithashighcurrentdensity,highenergyefficiency,andtheproductiswater,soithasnopollutiontotheenvironmentandisconsideredtobeenvironmentallyfriendly.PEMFChasawiderangeofapplication,bothasapowersourceforautomotive,aerospace,unmannedaerialvehicles,aswellasforpowergeneration,homeheatsupply,backuppower,etc.However,thedurabilityofPEMFCbatterieshasalwaysbeenahindrancetothecommercialproductionoffuelcells.ForPEMFCtomeetcommercialneeds,lifeexpectancyneedstomeetcertainconditions.Whenusedasapowersource,theminimumlifeexpectancyofPEMFCis5000h.Whenusedfordistributedgeneration,thelifeexpectancymustbeatleast4000h.
Inordertoachievethemaximumbenefits,somescholarshavebeeninvestigatingtheimprovementdurabilityofPEMFC.ThispaperisareviewofrecentworkdoneonacceleratedstresstestsinthestudyofPEMFCfuelcelldurability,withaprimaryfocusonthemaincomponentsofthemembraneelectrodeassembly(MEA).zhangreportedtherecentworkofacceleratedstresstestsinthestudyofPEMfuelcelldurability,n,differentdegradationmechanismsproposedinrecentpublicationsarebrieflyreviewed.Litsterfocusedonthecatalystlayerinaveryconstructivemannerbutpresentedalimiteddiscussiononthegasdiffusionlayer.Xiaoreviewedtestprotocolsofpolymerelectrolytemembranefuelcell.WanganalyzedthedurabilityofNafionaselectrolyte.Theresultsshowthatscanning1000circleCVinacidicsolutionenvironmentisanidealtestingmethodoflife.
Theintentofthispaperistoreviewthedurabilityoftheprotonexchangemembranefuelcell.TheworkingprincipleofPEMFCissummarizedinthispaper.Thetestmethodofdurabilityandthedegradationmechanismareanalyzed.Atpresent,theresearchfocusoffuelcelldurabilitymainlyincludeskeycomponentssuchasexchangemembrane,electrode,catalystandgasdiffusionlayer.
2PrincipleofPEMFC
PEMFCisadevicethatdirectlyconvertschemicalenergyintoelectricalenergy,usinghydrogenasfuelandoxygenasoxidant.WhenthePEMFCisworking,hydrogendiffusesthroughthegasdiffusionlayertotheanodecatalyticlayer.Underthecatalyticactionofthecatalyst,hydrogenloseselectronstoformH+,H+passesthroughtheprotonexchangemembrane,andpassesfromtheanodetothecathode.Theelectronsfirstdiffusethroughthecatalyticlayertothegas.Thediffusionlayeristransferredtothebipolarplate,andfinallytheexternalwireconnectedtothecollectorplatemigratestothecathode;atthecathode,oxygendiffusesthroughthegasdiffusionlayertothecathodecatalyticlayer,andunderthecatalyticactionofthecatalyst,oxygenisobtainedfromtheanode.ThemigratedelectronsandH+reacttoformwater,whichisdischargedwiththereactiontailgas.ElectronicmigrationoutsidethePEMFCandinternalH+migrationensureproperbatteryoperation.
Usually,theoutputvoltageofasinglePEMFCisonlyabout0.7V.Inordertomeettheneeds,inpractice,multiplePEMFCsareconnectedinseriesorinparalleltoformabatterystack.Inthisway,tensorevenhundredsofMEAscanbestackedtogether.Sincethisisamodularstructure,itiseasytoachievevariouscapacityrequirements,andmaintenanceandmaintenance.TheoutputofthePEMFCbatterystackisDC.WhenpoweringtheACequipment,itneedstobeinvertedintoAC.
3Durabilitytestmethod
DuetothenumerousfactorsaffectingthedegradationofPEMFCperformance,thedegradationmechanismsofthevariouscomponentsinvolvedaredifferent,alargenumberofexperimentshasbeendonebothathomeandabroad.
LuinvestigatedaavoltagedegradationmodelforPEMFCtackusedinafuelcellbus.PhaseIonsistsofidlingrunning,dynamicloadrunning,partialpowerrunningandphaseIIconsistsoffullpowerrunningandoverloadrunning.OnedrivingcycleconsistsoffourphaseIandonephaseII,andtheidlingconditionandfullpowerconditionaccountforahigherproportion,andtheidlingconditionandfullpowerconditionaccountforahigherproportion.Houintroduceda60KWfuelcellenginedevelopedinDICP.Inordertogethigherefficiency,theFCEwasoperatedunderdifferentpressure.Houconductedastudywitha20-cycletestunderthisconditions,theengineperformanceisstablebycomparingthevoltagevaluesatseveraloutputpowers.Thevoltagestandarddeviationis2.17voltsatratedoutputpower.HuangstudiedthedurabilitythePEMFCunderopencircuitvoltageoperationandrelativehumiditycyclingoperation.Theinfluenceofprotonexchangemembraneontheddurabilityofmembraneelectrodeassembly(MEA)hasinvestigatedunderOCVoperationandthemechanicaldegradationofthemembranehasstudiedunderrelatibehumditycyclingoperation.Finally,theinfluenceofbackpressureonthedurabilityofMEAhasinvestigatedunderOVCoperation.TheresultsindicatesthedurabilityofPEMFChasbeenimproved.
StandarddurabilityassessmentproceduresareimportantforresearchinPEMFC,andadvancedresearchintheUnitedStateshasdrivenresearchintothedurabilityoffuelcellsandtheircriticalcomponents.In2007,theUSDepartmentofEnergyreleasedthePEMFC'sdurabilitytestingstandardtestprocedure,withthemainpurposeoftestingtheresultsofitshydrogenenergyprogram.Thisstandardprocessispidedintotwoparts,oneforthefuelcellasawholeandtheotherfortestingthevariouscomponentsofthefuelcell.Basedinthepowderdemandsfromacardriving,thedynamicstresstestwasdevelopedinordertoassessthelong-timedurabilityofPEMFC.CAFEisacceptontheautomotiveindustrywhichisafuelemissionandeconomystandardofUSA.ThehighwaydrivingcycleandurbandrivingcylcesconstitutetheCAFE.TestingthedurabilityofPEMFCstackwithCAFEcanexaminethefuelcellsdegradationunderdifferenttypicalconditions,suchasdynamicloadconditions,start-stopconditions,idlestate,fullpowerconditions.
4Thedegradationmechanism
Thestudyofdegradationmechanismsisaprerequisiteforustomitigateperformancedegradation.Thestudyofdegradationmechanismismainlybasedonthedegradationmechanismofvariouscomponents,mainlydegradationofprotonmembrane,degradationofcatalystanddegradationofelectrodes.
4.1Protonexchangemembranedegradation
TheroleoftheprotonexchangemembraneistoconductprotonswhilesequesteringH2andoxidizingagents.Protonexchangemembraneshaveexcellentconductivity,lowfuelpermeability,highthermalstability,goodmechanicalpropertiesandelectricalinsulation.Thecommonlyusedprotonexchangemembraneistheperfluorosulfonicacid(PFSA)protonexchangemembranedevelopedbyDuPontCompany.ThePFSAprotonexchangemembraneconsistsofaPFSAresinwithahydrophobicpolytetrafluoroethyleneasthebackboneandahydrophilicsulfonicacidgroupasabranch.ThePFSAprotonexchangemembranehasexcellentprotonconductivityandlowfuelpermeability.However,thesulfonicacidgroupinthePFSAprotonexchangemembraneisunstablewhenthetemperatureistoohigh,andthesulfonicacidgroupintheSAprotonexchangemembraneiseasilyattackedbyfreeradicalattackduringtheactualuseofthePEMFC,andthedurabilityofthePEMFCislowered.Sex.Therefore,thedevelopmentofanewcompositeprotonexchangemembranebasedonPFSAresinhasbecomethefocusofresearch.Mcdonald'sstudyfoundthatafterprotonexchangemembranesundergo350temperaturecyclesof80°CCto-40°C,theprotonexchangemembranehasadecreasedprotonconductivity,alargegaspermeability,andadecreaseinmechanicalstrength.Whentheprotonexchangemembraneformsapinholeduetomechanicalattenuation,thepermeatefluxofthereactiongasisincreased,andthereactiongasisdirectlyburned,resultinginenthalpy.ThelocalhightemperatureonthesurfaceofthecatalyticlayerorthechemicaldecayoftheprotonexchangemembraneacceleratestheattenuationoftheMEA.
4.2Catalyticlayerattenuation
Theattenuationofthecatalyticlayerincludestheattenuationofthecatalystinthecatalyticlayer,thecorrosionofthecatalystcarboncarrier,andthedegradationofthefionresininthecatalyticlayer.TheattenuationofthethreeportionsleadstoadecreaseintheelectrochemicalreactionsurfaceofthecatalyticlayerandadecreaseintheperformanceofthePEMFC.
ThePtparticlesareeasilyaffectedbyimpuritygasesinthereactiongas,suchasgasessuchasCOandSO2.GasessuchasCOandSO2poisonthePtparticlesandreducethereactivityofPt,resultinginreversibledecayorirreversibledecayofPt,andevensintering,migration,andshedding.J.XiefoundthataftertheMEAsectionrunning1000h,theparticlesizeofthePtparticlesattheinterfaceincreases,andtheshapeoftheEFparticleschanges.ThechangeintheshapeoftheparticlesmaybecausedbythemigrationofionsofPttotheinterfacebetweenthefilmandthecatalyticlayer.ItisalsoobservedthatthePtparticlesintheinteriorofthefilmarealsorecrystallizedfromthemigrationofPtionsintothefilm.Thecarboncarrierisacommonlyusedcatalystcarrier,andthecarboncarriercanraisethespecificsurfaceareaofthecatalyst,reducetheagglomerationofthecatalystparticles,andimprovetheutilizationrateofthecatalyst.Typically,thecarbonsupportisasphericalparticleobtainedbypyrolysisofdifferentclasses,havingadiameteroflessthan30nm.Theoretically,whenthepotentialisgreaterthan0.207V,thecarboncarrierwillcorrode.NafionresinisanimportantpartoftheMEAcatalyticlayer,usuallyaccountingfor30%-40%wtanditscontenthasacriticalinfluenceforMEAperformance.Xiaousedsulfonatedpolyetheretherketoneasaprotonexchangemembranetoavoidprotonexchange.Thedecayofthemembranechangestoproducefluorideions,whichhasaneffectonthedegradationofNafioninthecatalyticlayer.ItisfoundthatNafioninthecatalyticlayerwillalsodegradetogeneratefluorideionsduetofreeradicals,resultinginadecreaseIntheECSAoftheMEAandadecreaseinperformance.
4.3Attenuationofthegasdiffusionlayer
Thegasdiffusionlayerisgenerallycomposedoftwolayersofbonding,onelayerofwhichishighlyconductiveandporous.
Thedielectriclayer,theotherlayerisamicroscopicporelayercomposedofcarbonparticlesandTeflontape,whichisakeycomponentofelectronconductionandwatertransfer.Manyresearchershaverecognizedthatinthelifeoffuelcellexperiments,thegasdiffusionlayerisintrinsicallylinkedtochangesinthestateofthewater(mainlymicron-nanoscalechanges).Duringtheexperiment,theoperatingenvironmentofthefuelcellgraduallychangedtheGDLfromhydrophobictohydrophilic,whichinturnaffectedtheoperationofthefuelcell.Forexample,theconvectionofgasandthediffusionofgasinthelaterstageoftheexperimentinterferedwitheachother.Pierrefoundthatafterrunning1000h,thehydrophobicityofthegasdiffusionlayerislowered.BorupreportedthatThehighertheoperatingtemperatureofPEMFC,thefasterthehydrophobicityofthegasdiffusionlayerdecreases.Itisreportedthatthedecreaseinhydrophobicity.Woodimmersedthegasdiffusionlayerinliquidwaterofdifferentoxygencontents.Theresultsshowthatthehighertheoxygencontentandtemperatureofthewater,theworsethehydrophobicityafterthegasdiffusionlayerisimmersedforaperiodoftime.ofthegasdiffusionlayerismainlyduetotheattenuationofthemicroporouslayer.
5conclusions
Toconclude,theworkingprincipleofPEMFCissummarizedinthispaper.Thetestmethodofdurabilityandthedegradationmechanismareanalyzed.
ThedurabilitystudyofPEMFCismainlypavingthewayforitscommercialization.MoreresearchneedstobedonetoimprovethedurabilityofPEMFC.ThedegradationmechanismofthePEMFCisthefocusofthefutureresearch.
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作者简介：张昊1993.06.29男汉黑龙江省牡丹江市硕士青岛大学SOFC电池连接体