燃料电池组件的孔结构表征

燃料电池组件的孔结构表征第1页/共67页IntroductionPorestructuregovernskineticsofphysicochemicalprocesses&Flowsofreactantsandproductsinfuelcells.QuantitativemeasurementofporestructureisessentialforDesign,developmentandperformanceevaluation.Technologiesforporestructuremeasurementarecurrentlybeingdevelopedtocharacterizethecomplexporestructureoffuelcellcomponents.Wewilldiscussseveralinnovativetechniquessuccessfullydevelopedandappliedforevaluationofporestructureoffuelcellcomponents.第2页/共67页ThroughPoreThroatDiameters,Distribution,GasPermeabilityandSurfaceAreaImportanceofSuchPropertiesThroughPores:FluidflowPoreDiameters:CapillaryforcesforliquidmovementThroatdiameters:SeparationofundesirableparticlesGaspermeability:OverallrateoftheprocessesThroughporesurfacearea:PhysicochemicalprocessesEffectsofstress,chemicalenvironments&temperature:Influenceofoperatingconditions第3页/共67页SuitableCharacterizationTechniquesAdvancedCapillaryFlowPorometryCapillaryCondensationFlowPorometryThroughPoreThroatDiameters,Distribution,GasPermeabilityandSurfaceArea第4页/共67页AdvancedCapillaryFlowPorometryForwettingliquid:WettingLiquidsfillporesspontaneouslyCannotcomeoutspontaneouslyApressurizedinertgascandisplaceliquidfromporesprovided: WorkdonebyGas=IncreaseinInterfacial FreeEnergyBasicPrinciple第5页/共67页AdvancedCapillaryFlowPorometryPressureneededtodisplaceliquidfromapore:p=4γcos

θ/D

p=differentialgaspressure

γ=surfacetensionofwettingliquid

θ=contactangleoftheliquid D=porediameterPorediameterisdefinedforallporecross-sections第6页/共67页AdvancedCapillaryFlowPorometry(Perimeter/Area)pore=(Perimeter/Area)cylindricalopeningPoreDiameter=DiameterofCylindricalOpeningSKETCH第7页/共67页AdvancedCapillaryFlowPorometryMeasureddifferentialpressure&gasflowthroughdry&wetsampleyieldporestructure第8页/共67页TheTechniqueAccuratePressuretransducersFlowtransducersRegulatorsControllersSophisticatedsamplesealingmechanismstodirectflowindesireddirectionsInternalcomputersTocontrolsequentialoperationsToexecuteautomatedtestsAdvancedFlowPorometers第9页/共67页TheTechniqueProperalgorithmsTodetectstablepressureandflowToacquiredataSoftwareToconvertacquireddatatoporestructurecharacteristicsTopresentdataintabular,graphicalandexcelformatsAdvancedFlowPorometers第10页/共67页AnExample:ThePMIAdvancedCapillaryFlowPorometer第11页/共67页ThePMIAdvancedCapillaryFlowPorometerFeatures:Sealingwithuniformpressurebypneumaticpiston-cylinderdeviceAutomaticadditionofmeasuredamountofwettingliquidatappropriatetime第12页/共67页ThePMIAdvancedCapillaryFlowPorometerAppropriatedesign&strategiclocationoftransducerstominimizepressuredropintheinstrumentMinimaloperatorinvolvementUseofsampleswithoutcuttinganddamagingthebulkproduct第13页/共67页AnalysisofExperimentalDataDryFlow,WetFlow&DifferentialPressureFlowrateanddifferentialpressuremeasuredinasolidoxidemicrofuelcellcomponent第14页/共67页AnalysisofExperimentalDataPorediametercomputedfrompressuretostartflow=ThroughPoreThroatDiameterThroughPoreThroatDiameter第15页/共67页AnalysisofExperimentalDataComputedfrompressuretoinitiategasthroughwetsampleTheLargestThroughPoreThroatDiameter(BubblePointPoreDiameter)Thelargestporesizeinasolidoxidemicrofuelcellcomponent第16页/共67页AnalysisofExperimentalData50%offlowisthroughporeslargerthanthemeanflowthroughporethroatdiameterMFPDcomputedusingpressurewhenwetflowishalfofdryflowTheMeanFlowThroughPoreThroatDiameterMeanflowporediameterofasolidoxidemicrofuelcellcomponent第17页/共67页AnalysisofExperimentalDataSmallestporeiscomputedusingpressureatwhichwetanddrycurvesmeetTheSmallestThroughPoreThroatDiameter&ThePoreDiameterRangePorediameterrangemeasuredinasolidoxidemicrofuelcellcomponent第18页/共67页AnalysisofExperimentalDataFlowDistributionFlowdistributioninamembraneTheflowdistributionisgivenbythedistributionfunction,fFfF=-d[(Fw/Fd)p×100]/dDFw=wetflow,Fd=dryflow第19页/共67页AnalysisofExperimentalDataFlowDistributionAreaunderdistributionfunctioninanydiameterrange=%flowthroughporesinthatrange第20页/共67页AnalysisofExperimentalDataPoreFractionDistributionPoreFractionNj=thenumberofthroughporesofthroatdiameterDjFj=[1/(4γcos

θ/pj)4][(Fw,j/Fd,j)–(Fw,j-1/Fd,j-1)]pj=differentialpressuretoremovewettingliquidfromporeofdiameterDj第21页/共67页AnalysisofExperimentalDataPoreFractionDistributionFlowfractiondistributionofamembrane第22页/共67页AnalysisofExperimentalDataGasPermeabilityFromDarcy’sLaw:F=k(A/2μ

lps)(Ts/T)(pi+po)[pi–po]

F=gasflowrateinvolumeatSTP ps=standardpressure Ts=standardtemperature k=permeability A=area

μ

=viscosity

l=thickness T=testtemperatureinKelvin pi=inletgaspressure po=outletgaspressure第23页/共67页AnalysisofExperimentalDataGasPermeabilityPermeabilitycomputedfromdryflowFlowratethroughadrysample第24页/共67页AnalysisofExperimentalDataThroughPoreSurfaceAreaKozeny-Carmanequationrelatesthroughporesurfaceareatoflow[F

l/pA]={P3/[K(1-P)2S2μ]}+[ZP2π]/[1-P)S(2π

p

ρ)

½]

F=flowrateinvolumeataveragepressure

p(p=[pi+po/2]), andtesttemperature P

=porosity S=surfaceareaperunitvolumeofsolid

ρ=densityofgasataveragepressure K=5 Z=(48/13π)Flowratethroughadrysample第25页/共67页AnalysisofExperimentalDataThroughPoreSurfaceAreaChangeofenvelopesurfaceareawithflowrate第26页/共67页EnhancedCapabilityAdvancedPorometerswithspecialattachmentscantestsamplesunderavarietyofconditions第27页/共67页EnhancedCapabilitySampleundercompressivestressorcycliccompressivestressCompression&CyclicCompressionPorometryEffectsofcompressivestressongaspermeabilityofGDL第28页/共67页EnhancedCapabilitySampleunderdesiredcontrolledhumidityandtemperatureControlledThermal&ChemicalEnvironmentPorometryThePMIFuelCellPorometer第29页/共67页EnhancedCapabilitySamplesexhibitingverylowflowratesFuelcellcomponentsMembranesDenseceramicsTightlywovenfabricsTinypartsSiliconwafersStoragematerialsMicroflowPorometrySmallflowratesthroughafuelcellcomponentmeasuredinthemicroflowporometer第30页/共67页EnhancedCapabilityIn-PlaneporestructureofsampleorporestructureofeachlayerofmultilayercomponentsFuelcellcomponentsBatteryseparatorsNonwovenfiltersFeltsPaperIn-PlanePorometry(DirectionalPorometry)Porestructureofeachlayerofaceramiccomponent第31页/共67页CapillaryCondensationFlowPorometryCapillaryCondensationFlowPorometryisarecentlypatentednoveltechniqueCondensationofVaporofaWettingLiquidinPoresVaporatp<po

cannotcondenseVaporatp<po

cancondenseinpores p=pressureofvapor,po=eq.vaporpressureBasicPrinciple第32页/共67页CapillaryCondensationFlowPorometryFreeEnergyBalanceshows→condensationoccuresinporessmallerthanDcBasicPrincipleDc=-[4V

γl/vcosθ

/RT]/[ln(p/po)] V=molarvolumeofcondensedliquid R=gasconstant

γl/v=surfacetension T=testtemperature

θ

=contactangle Dc=porediameter

第33页/共67页CapillaryCondensationFlowPorometryFlowofVaporthroughEmptyPoresAsmallimposedvaporpressuregradientcausesflowthroughemptyporesgreaterthanDcBasicPrinciple第34页/共67页TheTechniqueMeasuredvaporpressureinequilibriumwiththesampleyieldsDcMeasuredrateofpressurechangeinthedownstreamsideyieldsflowrate第35页/共67页AnExample:ThePMICapillaryCondensationFlowPorometer第36页/共67页AnalysisofExperimentalDataCondensationstartsatthethroatofathroughporeandpreventsgasflowDc=throughporethroatdiameterThroughPoreThroatDiameter第37页/共67页AnalysisofExperimentalDataMeasuredFlowRate=Flowthroughallpores>DcMolecularflowisapplicabletoflowthroughsuchsmallpores (F/AΔp)cumulative=(Ts/T)(π/12τpsl)(8RT/πM)½ [ΣD

DmaxNi(Di)3]A=areaofsample p=pressuredropacrossthesamplel=samplethickness T=testtemperatureinKM=molecularweight, Ni=numberofporesofdiameterDiF=flowrateinvolumeatSTP,psandTs

=averagetortuosityofporesandisequalto(L/l)whereListhelengthofcapillary,D=porediametercomputedbyaddingtoDcasmallcorrectiontermforthicknessofadsorbedlayerChangeofVaporFlowRate第38页/共67页AnalysisofExperimentalDataChangeofVaporFlowRateVariationofflowratewithporediameterFlowratethroughamembrane第39页/共67页AnalysisofExperimentalDataPoreDistributionExpressedintermsofdistributionfunction,ff=-d((F/AΔp)cumulative)/dDFlowdistributioninamembrane第40页/共67页AnalysisofExperimentalDataNumberofPoresofDiameter,DiNumberofporescomputedusingthefollowingrelationf=(Ts/T)(π/12τpsl)(8RT/

πM)½

[3Ni(Di)2]第41页/共67页StrengthsoftheTechniqueThediametersofporesdowntoafewnanometersandflowthroughthesesmallporesaremeasuredTestpressureonthesampleisalmostzeroExtremetestconditionsareavoidedThereisnostressonthesampleandstructuraldistortionordamagetothesampleisnegligible第42页/共67页StrengthsoftheTechniqueOnlythroughnanoporesaremeasuredandblindporesareignoredunlikethegasadsorptiontechniqueThroatdiametersaremeasuredAwidevarietyofvaporscanbeusedMeasuringtechniqueissimple第43页/共67页HydrophobicThroughandBlind

PoreVolumeandDistributionHydrophobicandhydrophilicporesarerelevantfor:WatermanagementTransportofreactantsReactionratesFlowratesofreactionproducts第44页/共67页VacuaporeBasicPrincipleHydrophilicporesarespontaneouslywettedbywaterHydrophobicporesrepelwaterbecauseγ(water/solid)>γ(gas/solid)PressureonwaterresultsinwaterintrusionIntrusionvolumeisporevolumePorediametercomputedfromintrusionpressureWorkdonebywater=IncreaseinsurfacefreeenergyD=-4γcos

θ/p第45页/共67页TheTechniqueRecentlypatentedtechniqueFeatures:Removalofairfromthepores,thesamplechamberandwaterApplicationofdesiredcompressivestressonthesampleOptionalin-planeintrusionofwater第46页/共67页TheTechniqueVacuapore第47页/共67页AnalysisofExperimentalDataOnlyhydrophobicthroughandblindporediameters

aremeasured.Measuredpressureyieldsporediameter

of

hydrophobicthroughandblindpores.Measuredintrusionvolumeofwater=Cumulativeporevolumeofhydrophobicthroughandblindpores.第48页/共67页AnalysisofExperimentalDataVolumedistributionisgivenasfunction,fvfv=-dV/dlogDHydrophobicandhydrophilicporedistributionsobtainedfromresultsofVacuaporeandMercuryIntrusionPorosimeter.第49页/共67页AnalysisofExperimentalDataHydrophobicpores: 50.3%,MPD=17.1mHydrophilicpores: 49.7%,MPD=<16.3mPoresizedistributioninGDLofaPEMFC第50页/共67页UniqueFeatureCapableofmeasuring:HydrophobiclargeandsmallporediametersIn-planeporestructureInfluenceofcompressivestressonporestructure第51页/共67页ThroughPoreVolume,DiameterandDistributionandLiquidPermeabilityImportantcharacteristicsofflowpermittingpores第52页/共67页LiquidExtrusionPorosimetryBasicPrincipleSamplesupportedbymembraneLargestMembranePore<SmallestSamplePorePoresofsample&membranefilledwithwettingliquidGaspressuredisplacedliquidfromsampleporesflowsoutthroughliquidfilledporesofmembraneGaspressuresufficienttoremoveliquidfromsampleporesdoesnotremoveliquidfrommembranepores第53页/共67页LiquidExtrusionPorosimetryBasicPrincipleMeasuredvolumeofliquidflowingoutofmembraneyieldsporevolumePressureyieldsporediameter p=4γcos

θ/D第54页/共67页TheTechniqueCylindricalsamplechamberholdsasupportscreenandmembraneChamberbelowthesupportscreenconnectedtoacontainerplacedonaweighingbalance第55页/共67页TheTechniqueO-ringsealsagainstthewallofthesamplechamberandthemembraneThepressureoftheinertgasonthewetsampleisincreasedtodisplaceliquidfrompores.第56页/共67页AnalysisofExperimentalDataMeasuredvolumeisthecumulativethroughporevolumeThroughPoreVolumePorevolumeoffivethinlayersofafuelcellcomponent第57页/共67页AnalysisofExperimentalDataAlldiametersbetweenthemouthandthethroataremeasuredDiametersbetweenthethroatandtheexitarenotmeasuredThroughPoreDiameterPorediametersmeasurablebyseveraltechniques第58页/共67页AnalysisofExperimentalDataThroughporevolumedistribution

functionfvThroughPoreVolumeDistributionPorevolumedistributionofToraypaperobtainedbyvarioustechniques第59页/共67页AnalysisofExperimentalDataPermeabilityisdefinedbyDarcy’slaw:F=k(A/

l)(pi-po) F=volumeflowrate k=permeability A=area

=Viscosity (pi-po)=differentialpressureInstrumentmeasuresliquidflowrate