Study of polyaniline doped with trifluoromethane sulfonic acid in gas-diffusion electrodes for proto
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JournalofPowerSources155(2006)
138–144
Studyofpolyanilinedopedwithtrifluoromethanesulfonicacidin
gas-diffusionelectrodesforproton-exchangemembranefuelcells
HusseinGharibia,∗,MohammadZhiania,AliAkbarEntezamib,
RasolAbdullahMirzaiec,MehdiKheirmanda,KarimKakaeia
aDepartmentofPhysicalChemistry,FacultyofScience,TarbiatModarresUniversity,P.O.Box14115-175,Tehran,IranbFacultyofChemistry,TabrizUniversity,Tabriz,IrancDepartmentofChemistry,FacultyofScience,ShahidRajaeeUniversity,Tehran,Iran
Received6February2005;accepted9May2005Availableonline28June2005
Abstract
Polytetrafluoroethylene(PTFE)-bondedgas-diffusionelectrodes(GDEs),modifiedwithpolyanilineasanelectronandprotonconductorinthecatalystlayer,arepreparedandevaluatedforuseinproton-exchangemembranefuelcells(PEMFCs).PolyanilineiscoatedontheGDEbyelectropolymerizationofanilineandtrifluoromethanesulfonicacidastheproton-conductivemonomer.Theelectrodesarecharacterizedbycyclicvoltammetry,current–potentialmeasurements,electrochemicalimpedancespectroscopy,andchronoamperometry.Thepolyanilineisfoundtobehomogenouslydispersedinthecatalystlayer,makingitagoodcandidateprotonandelectronconductor.UseofpolyanilineinsteadofNafioninthecatalystlayer,increasestheutilityoftheelectrocatalystby18%.TheresultsareconsistentwiththepresenceofpolyanilineasaconductivepolymerinthereactionlayerreducingthepolarizationresistanceoftheelectrodeincomparisonwiththatofacorrespondingelectrodecontainingNafion.Thus,thepresentresultsindicatethatPEMFCsusingpolyaniline-containingelectrocatalystsshouldgivesuperiorperformancetothoseusingcatalystscontainingtraditionalionomers.©2005ElsevierB.V.Allrightsreserved.
Keywords:Polyaniline(PANI);Nanofibular;Modifiedelectrode;Gas-diffusionelectrode;Proton-exchangemembranefuelcell;Nanostructure;Oxygenreductionreaction
1.Introduction
Platinumisthemostimportantcatalystusedingas-
diffusionelectrodes(GDEs)[1,2]forproton-exchangemem-
branefuelcells(PEMFCs).Thediscoveryinthe1980s
thatintroducinganionomer(liquidNafion)intoGDEs[3]
extendsthethree-dimensionalreactionzoneoftheelec-
trodeandleadstoasignificantloweringoftheplatinum
loadings,i.e.,fromabout4–10mgcm−2(platinumblack)to
about0.4mgcm−2orevenless(carbon-supportedplatinum).
Nafionmaybeappliedbyimpregnation,brushing,spraying,
orfloating/dippingtheelectrodeinasolutionoftheionomer.
∗Correspondingauthorat:DepartmentofChemistry,TarbiatModarresUniversity,P.O.Box14115-4838,Tehran14155,Iran.Tel.:+98216462548;fax:+98216462254.E-mailaddress:gharibi@irandoc.ac.ir(H.Gharibi).Severalstudieshaveexaminedtheinfluenceoftheionomer
contentinthecatalystlayeronGDEperformance.Inareview
ofdatafromvariousstudiesontheoptimumNafioncontent
ofthecatalystlayer,Antolini[4]concludedthatintroduction
oftheionomerintothecatalystlayerbyimpregnationgavea
loweroptimumNafioncontentthanintroducingtheionomer
byplacingitinthecatalystink.
Matsubayashietal.[5]reportedthatthevariationinelec-
trodeperformancewiththeamountofNafiondependsonthe
methodusedtointroducetheelectrolyte.Hsuetal.[6]stud-
iedtheeffectofNafionimpregnationofadualelectrodeby
cyclicvoltammetryanda.c.impedancemeasurements.The
maximumelectroactivesurfacearea(ESA)andtheminimum
ohmicresistanceofthecelloccurredat0.67mgNafionper
cm2.
Inallofthemethodsusedtodate,theNafionsolutionis
introducedintothecatalystlayerasaphysicalorchemical
0378-7753/$–seefrontmatter©2005ElsevierB.V.Allrightsreserved.doi:10.1016/j.jpowsour.2005.05.016H.Gharibietal./JournalofPowerSources155(2006)138–144139
mixture[7–9].Theuseofthisapproachhasthedisadvantages
thatitisdifficulttocontroltheamountofNafionapplied
andimpossibletoachieveahomogeneousdistributionofthe
ionomerinthereactivelayer.Asaresult,themassactivity
isdecreasedandhencethecostoffabricationisincreased.
TheidealcatalystlayerforaGDEwouldbegas-andwater-
permeable,andwouldconductbothprotonsandelectrons.
Electron–protonconductivepolymers,especiallypolyani-
line(PANI)dopedwithtrifluoromethanesulfonicacidasa
proton-conductingmonomer,aregoodcandidatesforresolv-
ingtheproblemsoutlinedabove.PANIanditsderivatives
havebeenconsideredpromisingmaterialsforbatteriesand
thecatalysisofelectrochemicalreactions[10–27].
Severalelectrocatalyticreactionshavebeeninvestigated
insystemscomprisedofnoblemetalsdispersedinelectron-
conductingpolymers.Thesereactionsincludethereduction
ofprotons[10,11]oroxygen[12–16],andtheoxidationof
hydrogen[17,18]orsmallorganicmoleculessuchasformic
acid[19,20],methanol[21–26],andethyleneglycol[27].In
addition,studieshavebeencarriedoutontheeffectofvary-
ingthecatalystcomposition(PANIorNafionwithPt)on
theoxygenreductionreaction(ORR)[28]andonthemodi-
ficationofGDEs[29].Inmostcases,thereactionrate(i.e.,
thecurrentdensity)wasincreasedandtheovervoltagewas
greatlyreducedbyintroducingPANIintotheelectrodes.