Htmwg May09 Nontraditional Membranes

7/30/2019 Htmwg May09 Nontraditional Membranes

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UNCLASSIFIEDUNCLASSIFIED

IntegrationofNonTraditionalMembranesintoMEAs

YuSeungKimSensorsandElectrochemicalDeviceGroup

LosAlamosNationalLaboratory

HighTemperatureMembraneWorkingGroupMeeting,WashingtonDC,May18,2009

1


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Outline Background MEA Fabrication Part1.MembraneElectrodeInterface

Interfacialresistancemeasurement ImpactofpoorMEAadhesion MethodofimprovingMEAadhesion

Part2. NonPFSAIonomers Ionomertocatalystratio Dispersingagent Oxygenpermeability Chainmobility

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UNCLASSIFIED

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.

3


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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

U N C L A S S I F I E D


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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


9/26

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

10


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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.

U N C L A S S I F I E D11


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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

13

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

15

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


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


DuetothelowerdensityofBPSH35,electrodewithlessamountofBPSH35performedbetter. OptimumBPSH35contentis~21wt.%(~27vol.%).



17/26

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.



18/26

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.


0.10.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4


1.6 1.8 2.0

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19/26

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.

U N C L A S S I F I E D 19


20/26

UNCLASSIFIED20

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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UNCLASSIFIED21

EffectofCathodeHumidificationonFuelCellPerformance


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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UNCLASSIFIED22

EffectofHydrophobicityofPolymers

Decafluoro based Polyaromatic

Hexafluoro bisphenol based Polyaromatic

Biphenyl based Polyaromatic

Courtesy: Profs. McGrath (VT) and Lee (GIST)

PFSAFully humidified cathode


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


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


23/26

UNCLASSIFIED

StateofWaterinESF100andBPSH35using2HNMR

23

Neat water

ESF-100

BPSH-35

BPSH35hasmoreboundwaterthanESF100whichpossiblyprohibitsoxygentransport.


24/26

+

UNCLASSIFIED

EffectofChainMobilityonBreakinProcess

BPSH35 O O SO2 O O SO2SO3HHO3S x1-x

CF2 CF2 CF CF2


CF3

x y

z

nCF2 CF2 CF CF2


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


25/26

Summary PooradhesionbetweenmembraneandelectrodemayresultinprematureMEAfailure(poorelectrodetransfer)duringMEAprocessingorgradualinterfacialdelaminationduring

longtermfuelcelloperation. Interfacialadhesioncanbeenhancedbythincoatinglayersorplasticizationofelectrode. Todate,propertiesandinteractionofnonPFSAionomerbinderswithfuelcellcatalystarepoorlyunderstood. SANSresultsindicatedthatdispersedandsolidionomerhaddifferentstructure(size,

micelleformationandphaseseparation)andmechanicalpropertiesdependingondispersingagent.

SolidNMRstudyindicatedthatstateofwatermaybeimportantfactorforelectrodefloodingwhichhaveobservedasapredominantfactor. Electrodeperformanceincreasedwithfluorinationofpolymers.

Sidechainmobilitymaygivecriticalinfluenceonelectrodeperformance. Moreinvestigationisneededinthisarea.



26/26

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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Htmwg May09 Nontraditional Membranes