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UNCLASSIFIEDUNCLASSIFIED
IntegrationofNonTraditionalMembranesintoMEAs
YuSeungKimSensorsandElectrochemicalDeviceGroup
LosAlamosNationalLaboratory
HighTemperatureMembraneWorkingGroupMeeting,WashingtonDC,May18,2009
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Outline Background MEA Fabrication Part1.MembraneElectrodeInterface
Interfacialresistancemeasurement ImpactofpoorMEAadhesion MethodofimprovingMEAadhesion
Part2. NonPFSAIonomers Ionomertocatalystratio Dispersingagent Oxygenpermeability Chainmobility
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IonomerBinderforNonTraditionalMembranes
HT IonomerBinder
HT Membrane
MEA for PEMFCs
Membrane
High proton conductivity at low RH
Good thermal/electrochemical stability
Low reactant permeability
Low electronic conductivity
Ionomer Binder
High proton conductivity at low RH
Good thermal/electrochemical stability
High reactant permeability
Good catalyst-ionomer interaction
Ionomerbinderhavingdissimilarstructurewithmembranesmaybedesirable.
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StrugglingforRobustMEAFabrications Gubleretal.,Hotpressingofradiationgraftedmembraneswasnotsuccessfulinourlaboratory.SuccessfulfabricationofhotpressedMEASwaspossiblewhenthinner
membraneswithlowerdegreeofgraftingwereusedFuelCells,(2005)5,317. Baeetal.,TheMEAcomposedofSPSgPPcompositemembranemaysufferfromthe
heterogeneousinterfacialstructureincreasingthecontactresistancebetweenmembraneand
catalyst
layer
J.
Memb.
Sci.
(2003),
220,
75.
Lufranoetal.Poorelectrode/electrolyte(sulfonatedpolysulfone)contactcausedfromthe
assemblyofanonperfluorinatedmembranewithacatalyticlayercontainingNafionionomerandlowchainsmobilityoftheseglassypolymersJ.Appl.Sci.(2000)77,1250.
LeNinivinetal.OptimizationofElectrodemembraneinterfaces(sulfonatedpolyphenylene)isnecessaryJ.Appl.Electrochem.(2004)34,1159.
Vernonetal...WiththisinmindoptimizationofMEAfabricationprocessesaswellasthedevelopmentofmorecompatibleionomermaterialsintheelectrodesmayproduceverysignificantimprovementsinperformanceforthehybridmembraneMEAJ.PowerSources(2005)139,141151.
Besseetal...Wehaveobservedthatthefuelcellperformancesofourpolyimidemembranesarerelativelydependentofprelimianryacidtreatment.Inordertoimprovetheelectrode/membraneinterface,athinsulfonatedpolyimidelayerwasdepositedontheelectrodesurfacebeforemakingtheassemblyNewMater.Electrochem.Sys.(2001),346.
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LANLMEAProcessingforNonTraditionalMembranes DirectMembranePainting
Y.S.Kim,J.Electrochem.Soc.151,A2150(2004) Catalystinkisdirectlypaintedonto
membranesusingvacuumplate Simpleprocess Difficulttocontrolcatalystloading Difficulttoprocesshighlywater
swollenmembrane Easytoisolatemembraneproperty
MostlyusedforDMFCapplications
Decaltransfer(Hotpressing)Wilson,USPatent5,211,984(1993)
Catalystinkispaintedondecalthentransfertomembraneusinghotpressing
Complexprocedure Precisecontrolofcatalystloading Easytoprocesshighlywaterswollen
membrane Electrodeadhesiontomembraneis
critical Difficulttoisolatemembrane
property MostlyusedforPEMFCapplications
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DirectMembranePaintingAdd water
Mixing Catalyst
+ Ink
Electrolyte Pt black catalyst
dispersionNafion 5%Water/alcohol >90%
Vacuum table
Teflon masking sheet
Ink Painting
75-80oC
current
time
Cell break-in
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DecalTransfer(Hotpressing)Glycerol
TBAOH
+ Mixing
Electrolyte Supported catalyst Catalyst Decal paintingPt 20%dispersion Ink & dryingCarbon 80%Nafion 5%
Water/alcohol >90%
time
current
Cell break-in Drying Acidif ication Hot pressing75oC/30 min 0.5M H2SO4 1.5 h 210oC few min.Under vacuum Water for 1.5 h
at boiling temp.
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UNCLASSIFIED
TwoMajorIssueswithDissimilarIonomerBindersHT IonomerBinder
HT Membrane
Interfacial Delamination
membraneanode cathode
GDL
PtCarbon
Binder
(K.More,DOEHydrogenandFuelCellsAnnualReport(2005))
Poor Performance due to lack of
Understanding of electrode structure
8
Catalyst/support dispersityCatalyst-ionomer interactionIonomer morphologyPorosityReactant/water permeability
Catalyst solubilityIonomer relaxationetc
Membrane-electrode interface
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UNCLASSIFIED
MeasurementofInterfacialResistance,RinterfaceRinterface=NonmembraneResistance ElectronicResistance
Non-membrane Resistance
Wet membrane thickness (m)0 50 100 150 200 250 300 350
H
FR
(c
m2)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Y = 7.2 x 10-4+0.035
non-membrane resistance
Electronic Resistance
Current (A)
0 5 10 15 20 25
Voltage(V)
0.00
0.02
0.04
0.06
0.08
0.10
0.12
cell 1
cell 2
cell 3
metal sheet replaced cell(including catalyst layers)electronic resistance
(27 cm2)
metal sheet replaced cell(excluding catalyst layers)
(35 cm2)
Rinterface for the example is 8 mcm2
Ref. Y.S. Kim and B.S. Pivovar, J. Electrochem. Soc. (2007) 154, B739.
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UNCLASSIFIED
RinterfacebetweenHCmembraneandNafionElectrode
Membrane Thickness (m)
0 50 100 150 200 250
HFR
(c
m2)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
1: BPSH-30
2: BPSH-35
3: BPSH-40
4: Nafion
1
2
30 2 4
0.03
0.040.05
0.06
0.07
0.08
4
1
2
3
4
Membrane (mS/cm) Rinterface(mcm2)
BPSH30 39 17
BPSH35 54 31BPSH40 78 43
Nafion 111 8
Conductivity, , andInterfacial Resistance, R
interface
SulfonatedPoly(Aryleneether)Sulfone(BPSHx)*
*Ref. M. Hickner et al. Chem. Rev. 104, 4587, 2004
SO 2
SO 3H
O
x
Oco
HO 3S
SO 2OO
1-x
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ImpactofMembraneElectrodeIncompatibilityonDecalTransferElectrode transfer@ 210oC hot pressing
Membrane Tg* Requiredhotpressing(oC)
Temp.(oC)Nafion memb./Nafion electrodeBPSH30 260 280BPSH
35 266 285
BPSH40 271 >295Nafion 120 140210
BPSH/Nafion electrode
HighTgHCmembranesrequirehigherhotpressingtemperature.
Hotpressingtemp.increaseswithdegreeofsulfonation.
LowsurfaceadhesionpropertyofHCmembranesmakesdifficultto100%electrodetransfer.
Ref. F.Wang et al. J. Memb. Sci. (2002), 197, 231.
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Method of Improving Interfacial Adhesion: 1. Thin Coating LayerBPSH/Nafion electrode with thin coating layersThin coating layer system*
Currentdensity(A/cm
2)
Cathode
0.25
0.0.2020
0.0.1515
0.0.1010
0.0.0505
0.2
0.1
Anode catalystcatalyst Low Proton Low 0.0layer
layer swelling exchange swelling 0 250 500 750 1000 1250 1500 1750 2000PEM membrane PEMTime (hour)
layer layer
*Y.S. Kim and B.S. Pivovar, US Patent Applications, LANL (2006) Stable DMFC performance (and HFR) wasobtained with thin coating layer system.
HFR
(Ohmc
m2)
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UNCLASSIFIED
LANLMEAFabricationStepsusingNontraditionalMembranes
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Is your membranehighly water swollen?
(i.e. >35 wt.%)
yes
no
Direct membranepainting
DecalTransfer
Does HFR increaseover time (under fully
humidification)?
yes Thin layercoating*
MEA testing
no
Are the electrodesadhered after acidification?
no
Plasticizedelectrode*
MEA testing
yes
* LANL Intellectual properties
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Part1.MembraneElectrodeInterface Interfacialresistancemeasurement ImpactofpoorMEAadhesion MethodofimprovingMEAadhesion
Part2. NonPFSAIonomers IonomertoCatalystRatio DispersingAgent OxygenPermeability ChainMobility
Electrode formulation & testing
conditions for electrode studies
Catalyst: Carbon supported platinum (20 wt.%)
Catalyst loading: 0.2 mg/cm2Anode ionomer: Commercial Nafion dispersionMembrane: Nafion 212MEA fabrication: LANL proprietary
Cell temperature: 80oC
Anode humidity bottle temperature: 105o
CBack pressure: 20 or 30 psiBreak in time: >14 h
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UNCLASSIFIED
NonPFSAElectrode Fact &Motivation
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Current density (A/cm2)
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
Cellpoten
tial(V)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
BPSH-35 bonded Pt/C (Pt 0.2 mg/cm2)
Nafion bonded Pt/C (Pt: 0.2 mg/cm2)
80oC
BPSH35
O O SO2 O O SO2
SO3HHO3S x1-x
CF2 CF2 CF CF2
OCF2 CF O(CF2)2 SO3-H
CF3
x y
z
n
CF2 CF2 CF CF2
OCF2 CF O(CF2)2 SO3-H
CF3
x y
z
n
Nafion
Electrodebondedbyhydrocarbonionomer(similarconductivitytoNafion)showedmuchinferiorperformancetotheelectrodebondedbyNafionionomer.
NoelectrodeionomerisavailableforhightemperaturemembraneswherethePFSAionomercannotbeused.
Membrane: Nafion 212
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EffectofIonomerContentonFuelCellPerformanceBPSH-35-bonded Electrode
CellPotential(
V)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
21
29
35
Ionomer content wt.%
Cell temp. 80oC with cathode bypass; backpressure: 30/30 psig
Catalsyt : 20% Pt/C (ETEK): 0.2/0.2 mgpt/cm2, ionomer: BPSH-35
ionomer Density(g/cm3) Wt.% Vol.%
Nafion 2 29 30BPSH35 1.3 21 27
29 4035 53
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Current density (A/cm2)
DuetothelowerdensityofBPSH35,electrodewithlessamountofBPSH35performedbetter. OptimumBPSH35contentis~21wt.%(~27vol.%).
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SANS Study of Nafion Dispersion
d/D(
cm-1)
1
0.1
0.01
0.0010.001 0.01
q (A-1)
SolventNMPEthyleneglycolWater/IPA(2:3)ButanediolGlycerol
Line represents slopecorresponding to sharpinterface betweensolvent and Nafion
0.1 1
Slope1.72.0
2.03.33.5
NMPdispersion:CoreShellCylinder*Structuresarevisualaidsreflectingcurrentunderstanding,andmaybelaterupdated
102
1239
27SharpinterfacebetweencoreandshellSLD*ofcore=~calculatedNafionbackboneSLDofshell=~solventNosolventpenetrationintothecoreSolventpenetratessidechains(lowslope)Glyceroldispersion:CylinderModel
14828
LessphaseseparationbetweenNafionbackboneandsidechainsGlycerolappearstopenetrateNafionlessthanNMP(highslope),butsomepenetrationmayoccur* Moreinformation:FC_16ChristinaJohnston,LANL,Wed.9:00AM.
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Effect of Dispersing Agent on Electrode PerformanceInitial Performance
Durability (potential cycling)
IR-corrected polarization curves Water/1-propanol/2-propanol0.901.1
InitialNafion electrode 1.0 After 1000 cycles0.85 After 3000 cycles
0.9After 10000 cycles
0.8
0.80
(V)
EIR-corrected
Cellpo
tential
Cellpoten
tial 0.7
0.6
0.5
0.4
0.75DISPERSION
N-methylpyrrolidone
water/2-propanol (1:3)0.700.3
glycerol 1 A cm-2: 60 mV loss0.2
0.650.1o
Cell temp. 80 C with fully humidified; backpressure: 30/30 psig2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Catalsyt : 20% Pt/C (ETEK): 0.2/0.2 mgpt/cm , ionomer: Nafion 212
Current density (A/cm2
)0.600.1 1 Glycerol
1.1
Initiali (A/cm2)
1.0 After 1000 cyclesAfter 3000 cycles
0.9After 10000 cycles Electrodes from NMP (and waterisopropanol) dispersion
0.8
exhibits good ORR kinetics while electrode from glycerol
dispersion have relatively good mass transfer. Electrode from water/2propanol showed poor potential
0.7
0.6
0.5
0.4
cycling durability while electrode from glycerol showed good
durability. 0.20.3 1 A cm-2: 30 mV loss* More information: FC_16 Christina Johnston, LANL, Wed. 9:00 AM.
U N C L A S S I F I E D
0.10.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Current density (A/cm2)
1.6 1.8 2.0
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HC Ionomer Dispersion in Various Dispersing Agent*IR-corrected polarization curvesEW Dispersing Dispe Mechanical Wettability
0.90medium rsion property 0.85
670 1,4 butanediol NA NA 0.801519 0.75
0.70670 Ethylene + Tough Good1519 glycol 670 Propylene + Tough Good
glycol1519 670 Glycerol + Tough Good1519 + EIR
-correc
ted
(V) 0.65
0.60
0.55
0.50DISPERSION
DMAc0.45
0.40483 + water/2-propanol (1:1)glycerol670 Water/iso + Brittle Poor
propanol (1:1)670 NMP + Tough Good1519 +670 DMSO +1519 +670 DMAc +1519 +*Y.S. Kim, T. Rockward, and K.S. Lee, US Patent Pending, LANL(2009)
0.35
0.30 oCell temp. 80 C with fully humidified; backpressure: 30/30 psig
0.25 Catalsyt : 20% Pt/C (ETEK): 0.2/0.2 mgpt/cm2, ionomer: BPSH-35
0.200.01 0.1
i (A/cm2)
Dispersing agent effect is much greater for BPSH35 electrode than Nafion but similar trend.
We have difficulties using waterbaseddispersion due to poor mechanical properties
and poor wettability.
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ChronoamperometryofOxygenonPt/NafionandPt/6F40
0 0.4 0.8 1.2
0
40
80
120
t-1/2
/ s-1/2
Current(n
A)
0.3 V
0.4 V
cv limiting
current
Ptglass
Ionomer
Oxygen
0
10
20
30
40
0 0.4 0.8 1.2
Current(n
A)
t-1/2
(s-1/2)
0.3 V
0.4 V
cv limiting
current
60 C, 60% RH, 100 m
(diameter) Pt UME(microdisk)Film thickness: Nafion 13.5 m, 6F40 - 26.5 m ;
Pt/Nafionelectrode Pt/6F40electrode
SignificantlyloweroxygenreductioncurrentsforthePt/6F40thanthoseforpt/Nafionindicatessignificantlyloweroxygenpermeabilityof6F40tooxygen.
NonlineariltyandcurrentdecreaseofPt/NafionbeyondthecvlimitingcurrentindicatessignificantpolymerchainreorganizationofNafionduringchromoamperometryprocess.
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EffectofCathodeHumidificationonFuelCellPerformance
Current density (A/cm2)
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Cellpotential(V)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
HFR
(c
m2)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
no humidified cathodefully humidified cathode
cell temp. 80oCcatalsyt : 0.2 mg/cm2 Pt/C
membrane Nafion 212electrode binder:BPSH-35 (27 vol.%)back pressure 30 psig
Redu
ced R
H
HydrocarbonbondedelectrodeshowsbetterperformanceatlowRHconditions,duetobettermasstransfer
GoodchancetoreplacePFSAbondedelectrodewiththermallystableHC bondedelectrodeforhightemp.andlessRHfuelcells
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EffectofHydrophobicityofPolymers
Decafluoro based Polyaromatic
Hexafluoro bisphenol based Polyaromatic
Biphenyl based Polyaromatic
Courtesy: Profs. McGrath (VT) and Lee (GIST)
PFSAFully humidified cathode
Current density (A/cm2)
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Cellpotential(V)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
No humidifed cathode
PFSA
Decafluoro
Hexafluorobiphenyl
PFSA
Decafluoro
Hexafluorobiphenyl
Current density (A/cm2)
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
C
ellpotential(V)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
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UNCLASSIFIED
StateofWaterinESF100andBPSH35using2HNMR
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Neat water
ESF-100
BPSH-35
BPSH35hasmoreboundwaterthanESF100whichpossiblyprohibitsoxygentransport.
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UNCLASSIFIED
EffectofChainMobilityonBreakinProcess
BPSH35 O O SO2 O O SO2SO3HHO3S x1-x
CF2 CF2 CF CF2
OCF2 CF O(CF2)2 SO3-H
CF3
x y
z
nCF2 CF2 CF CF2
OCF2 CF O(CF2)2 SO3-H
CF3
x y
z
nNafion
PtSO3H
PtSO3H
Pt
SO3H
Pt
SO3H
Beforebreakin Afterbreakin
Beforebreakin Afterbreakin
Break in at 0.7 V
time (h)
0 20 40 60 80
current(A
)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
BPSH-35
Nafion
6F-40
Nafion
6F-40
BPSH-35
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Summary PooradhesionbetweenmembraneandelectrodemayresultinprematureMEAfailure(poorelectrodetransfer)duringMEAprocessingorgradualinterfacialdelaminationduring
longtermfuelcelloperation. Interfacialadhesioncanbeenhancedbythincoatinglayersorplasticizationofelectrode. Todate,propertiesandinteractionofnonPFSAionomerbinderswithfuelcellcatalystarepoorlyunderstood. SANSresultsindicatedthatdispersedandsolidionomerhaddifferentstructure(size,
micelleformationandphaseseparation)andmechanicalpropertiesdependingondispersingagent.
SolidNMRstudyindicatedthatstateofwatermaybeimportantfactorforelectrodefloodingwhichhaveobservedasapredominantfactor. Electrodeperformanceincreasedwithfluorinationofpolymers.
Sidechainmobilitymaygivecriticalinfluenceonelectrodeperformance. Moreinvestigationisneededinthisarea.
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AcknowledgmentsBryanS.Pivovar(NREL)
JamesE.McGrath(VirginiaTech)ChulSungBae(UNLV)
MichaelGuiver(CanadaNRC)JaeSukLee(GIST)
KwanSooLee(GIST,LANL)TommyRockward(LANL)AndreaLabourieu(LANL)
BruceOrler(LANL)CindyWelch(LANL)
MarilynHawley(LANL)RexHjelm(LANCE,LANL)ChristinaJohnston(LANL)
JerzyChilstunoff(LANL)NancyGarlend
(DOEEEREProgram)
UN
C
LA
SSIFIED
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