Computationaldesigntoimprovepolymerelectrolytefuelcellperformancebyflowfieldmodification

Abstract

Fuelcellisoneofthepromisingenergyconversiondevicewhichgenerateselectricenergyfromchemicalenergyofhydrogen.Becauseitconvertschemicalenergyintoelectricenergydirectlywithelectrochemicalreactionofhydrogenandoxygen,itsenergyconversionefficiencyishigh.Besides,sinceitproducesonlywaterasby-products,itiseco-friendlyenergy.Polymerelectrolytefuelcell(PEFC)isatypeoffuelcellwhichuses polymermembraneaselectrolyte.Inadditiontogeneraladvantagesoffuelcell.ThePEFChasmanyadvantagessuchashighpowerdensity,faston-offtime,excellentdynamicresponseandwideapplicability.ThemanyadvantageshavedirectedalotofattentionsofresearchersandengineerstothePEFCandmanystudieshavebeenconductedbytheresearchersandengineerstoimprovethePEFCperformance.

TheoneresearchstrategytoupgradethePEFCperformanceisimprovingmasstransfercharacteristics.Themasstransfermeansreactantsupplyandproductdischarge.ThePEFCperformanceisaffectedbytheconcentrationofreactantatreactionsiteandthereactantconcentrationisdeterminedbymasstransfercharacteristics.VaporthatistheproductofPEFCcondensesintoliquidwaterwhenthepartialpressureexceedsthesaturationpressure.BecausetheliquidwaterdegradesthePEFCperformancebyhinderingreactantsupplyandcoveringreactionsite,itisimportanttodischargetheproducteffectivelyandthisproduct dischargeisaffectedbymasstransfercharacteristics.Inthisdissertation,fivestudiesthatimprovedmasstransfercharacteristicsbymodifyingflowfieldincludinggasdiffusionlayer(GDL)andchannelwereconducted.

Firstly,theGDLpropertiesandchanneltypesweretreatedassubjectforstudy.ByapplyingthevariousvaluesofGDLpropertytoserpentine,parallelandinterdigitatedchannelwhicharecalledasconventionalchanneltype,itwasconfirmedthattheeffectofGDLpropertyonthePEFCperformancechanged.GDLpermeabilityandGDLshapewhicharethepropertiesofGDLitselfwereselectedandstackingpressure,whichisexternalconditioncausingGDLdeformationandGDLpropertychange,wasalsoselectedastheGDLpropertiesforanalysis.TheGDLpermeabilityofperpendiculardirectionofmainflowwasdominantpermeabilitywhichremarkablyinfluencesthePEFCperformanceatserpentinechannel.However,thePEFCperformancehavingotherchanneltypehardlychangedbyGDLpermeabilityvariation.TheGDLshapewhichhassameshapetorib upgradedtheperformanceofallPEFCshavingdifferentchanneltypesbyimprovingmasstransfercharacterization.Finally,itwasconfirmedthattheoptimalstackingpressurewasdifferentdependingonthechanneltypeandcellvoltagecondition.

Then,parallelchannelwithvariousbafflepatternandmetalfoamflowfieldwithserpentinestructureforevenreactantdistribution,whichareunconventionalchanneltype,werestudied.ThePEFChavingparallelchannelwasimprovedbyapplyingbafflesandthedegreeofimprovementwaschangedbybafflepattern.Whenthebafflesareappliedasstaggeredpatternwithwidespacingbetweenthebaffles,theparallelchannelPEFCshowedhighestcurrentdensity.Metalfoamflowfieldhavingserpentinestructureasflowguideshowedbetterperformancethanmetalfoamflowfieldwithoutserpentinestructureandwhenthenumberofturnsofserpentinestructureincreases,thePEFCperformanceincreasedwithpressuredrop.

ThestudiesinthisdissertationdemonstratedthattheeffectofGDLpropertieschangebychanneltypeandsuggestedthesignificantparametersinunconventionalchanneltypeandtheeffectofparameters.Throughthestudies,itisexpectedthattheguide,whichhelpstheresearchersselectoptimalGDLpropertyandchanneltypewassuggestedandtheunderstandingofvariousparametersimprovingPEFCperformancewasbroadened.Accordingly,theworkcontributestowardcommercializationofPEFCbypresentingtheeffectivewayofhighperformancePEFCdesignandimprovingPEFCperformancehavingunconventionalchannel.