Carboxylated Carbonized Polyaniline nanofibers as Pt-Catalyst Conducting Support for Proton Exchange Membrane Fuel Cell

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SyntheticMetals188 (2014) 21–29

ContentslistsavailableatScienceDirect

Synthetic

Metals

j o u r n a l ho me p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s y n m e t

Carboxylated

carbonized

polyaniline

nanoﬁbers

as

Pt-catalyst

conducting

support

for

proton

exchange

membrane

fuel

cell

Yen-Zen

Wang

a

_,

_Kai-Jay

_Chang

a

_,

_Li-Fan

_Hung

b

_,

_Ko-Shan

_Ho

b,∗

_,

_Jing-Ping

_Chen

b

_,

Tar-Hwa

Hsieh

b

_,

_Liang

_Chao

c

a_Department_of_Chemical_and_Materials_Engineering,_National_Yun-Lin_University_of_Science_and_Technology,_640,_Yun-Lin,_Taiwan

b_Department_of_Chemical_and_Materials_Engineering,_National_Kaohsiung_University_of_Applied_Sciences,_415,_Chien-Kuo_Road,_Kaohsiung_80782,_Taiwan c_Department_of_Tourism_and_Hospitality,_Taipei_Chengshih_University_of_Science_&_Technology,_Peito,_Taipei₁₁₂₀₂_Taiwan

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received19September2013

Receivedinrevisedform1November2013 Accepted14November2013

Available online 15 December 2013 Keywords: Polyaniline Carbonization Carboxylation Electrocatalystsupport

a

b

s

t

r

a

c

t

Polyanilinebasednanoﬁbers(PANF)preparedviaemulsionpolymerizationwithoutauxiliaryorganic

sol-ventarecarbonizedtobecomea1Dandnitrogen-containingelectrocatalystsupportforprotonexchange

membranefuelcell.ThecarbonizationcansigniﬁcantlyincreasetheconductivityofPANFbutalsocreate

hydrophobicsurface,causingmuchlessPt-loadingreducedbyethyleneglycol.Carboxylicacidgroups

aresubsequentlygraftedtothesurfacebyreﬂuxinginsulfuricandnitricacids,whichallowcarbonized

PANFtobedispersedintheaqueoussolutionandprofoundlyincreasethePt-loading.

CarboxylatedcarbonizedPANFelectrocatalystsupportdemonstratesbetterelectrochemicalactivity

thatpreparedfromcarbonblack(VulcanXC-72)inthecyclicvoltaicandORRtesting.Thesingle-cell

performanceillustratesahigherpowerandmaxcurrentdensityforMEAmadeofcarboxylatedcarbonized

PANFthanthatofcarbonblack.Besides,theMEAexperiencesneitheraseriouspowerdensitylossathigh

currentdensity(inthecathode)northeaccumulationofwaterproductinthecathodeofMEA.

1. Introduction

Thelong-standing prospectiveadvantages of replacingfossil fuelswithhydrogenfuelcansubstantiallyreducegreenhousegas emissionsandsmogpollution[1–3].Therefore,hydrogenfuelcell technologieshavebeenappliedinmanyareasforpossiblesolutions totheseproblems[4].

Attention has recently been paid on hydrogen and oxygen systemofprotonexchangemembranefuelcells(PEMFCs)under theconsiderationsofbothtransportationandemergencyelectric power sources owing to its friendly by-products, high power density, low noise, and low operating temperatures. However, one ofthe main problemsto commercializePEMFCs is howto producelow-costPt-catalystswithhighcatalyticefficiency and lastingdurabilityundertheworkingorharshconditions[5].The performanceofthePEMFCsdependsonthepropertiesofthegas flowcharacteristicsinthemembrane electrodeassembly(MEA) [6]inwhichinterfacialareasbetweenthereactant,electrolyteand catalystitself,theso-calledtriple-phaseboundary,playimportant rolesonefficiencyofPEMFCs.Tomakeagooduseofthecatalyst, theboundariesbetweenthesedifferentphasesintheMEAsneed tofindgoodionicandelectronicconductingmediatocreatelots

∗ Correspondingauthor.Tel.:+88673814526x5122;fax:+88673830674. E-mailaddress:[email protected](K.-S.Ho).

ofconnectedpathwaysfortheprotonstopassthroughthe elec-trolyteandfortheelectronstotransportthroughthethree-phase electrodestotheoutercircuit. Consequently,connectedcatalyst supportswithhighporosityandconductivityneedtobeprepared toaccommodatemorereactants(fuelgases)toreactandallowthe producedelectronsprotons,andwatertotransportinshortertime. Therefore,weneedconductingcatalystsupportswithnanoscaled porestoacceptandeffectively dispersethereducedPtonthem [7].Atpresent,catalystmaterialforMEAispreparedbyloading nanoscaleplatinum (Pt) particlesonthe surfaceof conducting/ nanostructure carbon black (CB) support in PEMFC. However, adoptingCBasthefuelcellcatalystsupportstillhassome disad-vantages.Forexample,theparticulateCBcansigniﬁcantlyinterrupt thepassingofelectronstotheoutercircuitsincesomeoftheCB particlesdonottouchwitheachother.Meanwhile,carbonsupport inthecathodeissubjectedtoseverecorrosioninthepresenceof waterandproducescarbondioxideathighperformingtemperature [8–10].Thiseffectdeteriorates theperformance ofthecatalysts andshortensthelifetimeofPEMFCs.Eventually,Pt/Ccatalystisstill providedwithahighprice,whichhasalreadydelayedthe com-mercializationofPEMFC.Therefore,cheaperPt-catalystsupporting materialwhichcanresistwatercorrosionattheworking tempera-tureisurgentlyneededtoreplaceCB,andconductingmetaloxides andconductingpolymersaresomeofthecandidates[7,11,12].

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22 Y.-Z.Wangetal./SyntheticMetals188 (2014) 21–29

protection,electrochemicaldisplays,energyconversions, intercon-nectiontechnology,microelectronics,andsensors[13–17].Among theconducting polymers, cheap polyaniline and its derivatives [18,19]arequaliﬁedcandidatesbecauseoftheirhighsurfacearea andporositywhenpreparedontheelectrodesubstrateviasimple electrochemicalpolymerizationinacidicmedia[20].

Anotherapproachtoobtainpolyanilineswithconductingand stablethree-dimensionalnanostructureistochemicallyprepare conductingpolyanilinewithnanofibrousmorphology(PANF)asthe supportforfuelcellcatalysts.Micheletal.[7]introduceda func-tionalizedPt/PANFcompositeanddemonstrateditshighfuelcell performanceandhighPtutilization.Wolzetal.[21]reportedusing polyolreducingmethodtodepositPtnanoparticlesonPANFand single-walledcarbonnanotubes(SWCNTs)tobuildupalternating layersofPANIsupportedcatalyst,it resultsin highpower den-sities.Huangetal.[22] investigatedthemorphology-dependent electrochemical properties of polyaniline micro/nanostructures ascatalystsupporters inDMFC applications.Quet al.[23] pre-paredcore–shellpolyaniline/VulcanCarboncompositestructures byin situ chemical polymerization, followed by thedeposition ofPtparticlestoimprovetheCOanti-poisoningabilityand cat-alyticefficiencyofthePt-catalyst.Yli-Rantalaetal.[24]prepared PtNPs/C-PANI/graphitized-CNFsasahighlyefficientcatalystwith superiorthermalstabilityandcorrosionresistanceforPEMFC.In comparisonwithaconventionalPtNPs/Ccatalyst,PtNPssupported onC-PANImaterials,modifiedbyachemicaltreatmentwithNaOH, H2O2,orHNO3 atroomtemperature,providedupto34%higher powerdensityinPEMFC[25].

However, the poorer conductivity of polyaniline can cause the slow electron transportation during redox reaction and signiﬁcantly reduce the power supply of PEMFC. Recently, carbonizationofnanoﬁbrousnitrogen-containingconducting poly-merstoincreaseitsconductivitybutretainsomeoftheN-related compositionaftercarbonizationathightemperaturehasopened newperspectivesforPANFtobeabettercatalystsupportmaterial thanCB[26].Conductingcarbonizedpolyanilinenanotubes pre-paredbyMentus etal.[27],presenta newnitrogen-containing material which is considered as a promising candidate for Pt support.Gavrilovetal.[28]preparedthenitrogen-containing car-bonizednanotube/nanosheetpolyanilineasanewcarbonaceous supportforPtnanoparticles.Highelectrocatalyticactivityofthe PtNPs/CarbonizedpolyanilineelectrocatalysttowardORRinboth acidicandalkalinemediawasclearlyseen.

ThecommercialPt/Ccatalyst is usuallyprepared byloading reducedPtatomsontothesurfaceofaCB(VulcanXC-72)whose purecarbonstructurecanbeerodedduringperformingofFCand causeasigniﬁcantconcentrationpolarizationofoxygenreduction inthecathode.Inthisstudy,wetrytoreplaceCBwithPANFinthe preparationofanMEAofPEMFCtoavoid thedegradation (cor-rosion)of theelectrode materialsandreducetheconcentration polarizationwiththeN-relatedgroupsofPANF[27,28].Various propertiessuchas,conductivity,surfacearea,surfacepore diame-tersofthecatalystsupport,whichhaveconnectionswiththe%and dispersibilityofPt-loading,andelectrochemicalactivitiesincluding performanceofthesinglecellofPEMFCwillbestudiedaswell.

2. Experimental 2.1. Materials

Theanilinemonomer(TOKYOKASEIKOGYOCO.)wasdistilled under vacuum before use. Ammonium persulfate (APS, Showa ChemicalsInstrumentCo.),para-phenolsulfonicacidhydrate(PSA, Tokyo Chemical Industry), hydrogen hexachloroplatinate (IV) hexahydrate (H2PtCl6·6H2O, Aldrich), ethylene glycol (EG, J.T.

Baker),hydrochloricacid(HCl,Riedel-deHaën(RDH)),Nitricacid (HNO3, Riedel-de Haën (RDH)),Sulfuric acid (H2SO4, Riedel-de Haën(RDH))wereusedwithoutfurtherpuriﬁcation.

2.2. SynthesisofPANF

PANF were prepared through an emulsion polymerization method,describedinpreviouspublications[29–32].

The only difference from the previous preparation of PANF was we replace para-phenolsulfonic acid hydrate with n-dodecylbenzenesulfonicacidasthedopingprotonicacid. 2.3. CarbonizationandcarboxylationonPANFelectrocatalyst supports

2gPANFpowderpreparedin2.2 wascarbonizedinanoven at 1100◦C in a nitrogen atmosphere (CPANF) [26]. Then 0.5g ofCPANF wasmixedwithmixture ofconcentrated 200mL1M HNO3 andH2SO4 (3:1)andultrosonicatedat0◦Cwaterfor12h underultrasonication.Finally,theobtainedacidtreated polyani-line(CPANF-COOH)waswashedwithde-ionizedwateruntilthe ﬁltratebecameneutralandtheﬁltercakesweredriedinanoven at60◦Cfor12h.

2.4. Platinumdepositedonvariouspolyanilines

Ptcontainingpolyanilinecompositeswerepreparedby reduc-ing a 0.02mol hydrogen hexachloroplatinate (IV) hexahydrate (H2PtCl6·6H2O)with20mLofethyleneglycol(EG)inthepresence of16mgofsuspendedneatPANF(orCPANF,CPANF-COOH) pow-dersandmixedundersonicationfor20min.TheH2PtCl6aqueous solutionwasdropwiseaddedtotheEGandelectrocatalystsupport (polyanilines)mixturewhichwasundervigorousstirringfor1h. ThensomeNaOHwasintroducedtoadjustthepHoftheEGsolution toabove11.Thesolutionwasthenheatedto170◦Candreﬂuxing for2h.TheobtainedPtcompositesnamedasPt/PANF(orPt/CPANF, Pt/CPANF-COOH)wereisolatedbyﬁltrationandwashedwith de-ionizedwater,driedat60◦Covernight.Theoretically,20wt%(or 25wt%)ofPtwillbepresentintheobtainedPt/polyaniline com-positeifitisfullyreducedbyEG.

Forcomparison,PtionswerereducedontoVulcanXC-72CBat thesameH2PtCl6acidconcentrationandconditions.

2.5. Materialscharacterization 2.5.1. FTIRspectroscopy

Thefunctionalgroupsofcarbonizedandcarboxylatedsamples werecharacterizedbyFTIRspectroscopy.TheFTIRspectrawere recordedonanIFS3000v/sFourier-transforminfrared spectrome-teratroomtemperature.

2.5.2. Ramanspectroscopy

TheRamanspectraofneatanddegradedsampleswerecarried outbyaTriax550spectroscopywithagreenlaserlightsourceof 520nmwavelength.Thesampleswerepressedintotabletsbefore exposingtoRamansource.

2.5.3. Electronspectroscopyforchemicalanalysis(ESCA)

ThedifferentbindingenergyspectraofC1sofvarious,which wereusedtoestimatethepercentageofcarbon,carboxylicgroups, wereanalyzedbyanESCAinstrumentofFison(VG)-Escalab210 usingAlK_␣X-raysourceat1486.6eV.Thepressureinthechamber wasmaintainedunder10−6Paorlowerduringthemeasurement. Atabletsamplewaspreparedbyastapler.Thebindingenergiesof theC1saround285eVwererecorded.

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Y.-Z.Wangetal./SyntheticMetals188 (2014) 21–29 23 2.5.4. SEM(scanningelectronicmicroscopy)

ImagesofvariousPANF,preparedfromstrewnoncarbonictape andfollowedbypostingonferricstage,weretakeninaField Emis-sionSEM,HRSEM(HITACHIS-4200:acceleratingvoltageof15kV). 2.5.5. BET(Brunauer–Emmett–Tellerspeciﬁcsurfacearea

analyzer)

Nitrogenadsorptionisothermsweremeasuredwithan auto-matedgassorptionsystem(Micromeritics;ASAP2101)keptatlow temperatureinliquidnitrogen.Thespeciﬁcsurfaceareawas cal-culatedusingBrunauer–Emmett–Teller(BET)approach.

2.5.6. Conductivity

A4-probesMilliohmmeter(LUTROMO–2001)wasusedto mea-suretheconductivityofPANF,CPANF,andCPANF-COOHpowders whichwerepressedintotabletsbeforemeasuring.Theconductivity ()wasobtainedfromthefollowingequation.

= L R/A

whereLandAarethethicknessandcross-sectionareaofthetablet sample,respectively.AndRistheresistanceobtainedfrom conduc-tivitymeter.

TheconductivityofallsamplesisexpressedinS/cmunit. 2.5.7. FTIRspectroscopy

Thefunctionalgroupsofcarbonizedandcarboxylatedsamples werecharacterizedbyFTIRspectroscopy.TheFTIRspectrawere recordedonanIFS3000v/sFourier-transforminfrared spectrome-teratroomtemperature.

2.5.8. WXRD(wideangleX-raydiffraction)

Ancoppertarget (Cu-K␣)RigakuX-raysourcewitha wave-lengthof1.5402 ˚Awasusedfordiffraction.Thescanningangle(2) startedfrom5◦ to100◦ withavoltageof40kVandacurrentof 30mAat1min−1.

2.5.9. TEM(transmissionelectronicmicroscopy)

Samplesforﬁeld emissiontransmissionelectronmicroscope, HR-AEM(HITACHIFE-2000)wereﬁrstdispersedinacetoneand putoncarbonic-coatedcoppergridsindropwisebeforesubjecting totheemission.

2.5.10. TGA(thermogravimetricanalysis)

The thermal degradation behavior of various Pt/polyaniline compositesandPt/XC-72wereexaminedbyTGA(TASDT-2960) thermograms.TheamountofPtdepositedonthesurfaceof cata-lystsupportswerecharacterizedbytheresidualweightat800◦C withaheatingrateof10◦Cmin−1underpurgingair.

2.6. Electrochemicalcharacterization

Cyclicvoltammetry(CV)methodwasusedtodeterminethe active electrochemical surface area of the catalyst supports in theelectrode.Theperformanceoftheelectrocatalystsupportwas testedwithathree-electrodesystem.Theworkingelectrodewith a square areaof 1.5cm2 _was_prepared _as_follows. _Ag/AgCl _and platinumwirewereusedasthereferenceandcounterelectrode, respectively.Theelectrochemicaltestwascarriedoutina poten-tiostat/galvanostat(Autolab-PGSTAT30EcoChemie)in1MH2SO4 solutionandvariouscyclicvoltammogramswereobtainedwith potentialscannedbetween_−0.2and1.2Vatasweepingrateof 50mVs−1.Thecatalystinkwaspreparedbymixing3mgsupport powderinisopropanolandstirreduntiluniform.Subsequently,5%

Table1

Propertiesofvariouselectrocatalystsupports.

NeatPANF CPANF CPANF-COOH XC-72 BETsurfacearea(m2_/g) ₄₀ ₁₈₈ ₆₈₉ ₂₅₄

Porediameter( ˚A) 241 66 36 109 Conductivity(S/cm) 0.032 6.667 1.786 4.167

Naﬁonsolutionwasaddedintothemixtureasbinderandthe

mix-turewasultrasonicatedfor1h,theobtainedinkwasuniformlycast

onthecarbonpaperforCVtest.

The electrochemicalactivitiesof thePt-electrocatalysts with

differentPANFsupportsweremeasuredusingarotating-disk

elec-trode(RDE)operatedat1600rpminO2-saturated0.5MH2SO4.The

oxygenreductionreaction(ORR)currentsatthemeasuredvoltage

range(0.5∼1.0V)foreachelectrocatalystmaterialwererecorded.

2.7. MEApreparation

ANaﬁon®₂₁₂_sheet_purchased_from_Ion_Power_Inc.,_New

Cas-tle,DE,USAwasusedasthepolymer exchangemembranes.In

ordertoremovethesurfaceorganicimpuritiesandtoconvertthe

membranes intoprotonated (H+₎_form _for _use_in _the_PEM, _the

Naﬁon-212(4×4cm2₎_membrane _was_treated _at₇₀◦_C _in₅_wt%

H2O2aqueoussolutionfor1h,followedbysubmergedin1MH2SO4

solutionfor1h,respectivelyandsubsequentlythetreated

mem-branesweredippedindistilled waterfor15minthenstoredin

de-ionizedwater.Thecatalystinkswerepreparedbymixing20mg

Pt/PANF(orPt/CPANF,Pt/CPANF-COOH)powdersinanisopropanol

solutionandstirredmechanicallyuntiluniformand5%Naﬁon

solu-tionwasaddedintothemixturefollowedbyultrasonicationfor1h.

Similartodoctorbladecoating,thecatalystinkswaslayerbylayer

coatedonbothsideofthetreatedNaﬁonsheetasanodeand

cath-odeelectrodes(2×2cm2_),_respectively_and_hot_pressed_at₁₄₀◦_C

with70kgcm−2for5minintoanMEA.

2.8. Single-cellperformancetesting

TheMEAwasinstalledinafuelcellteststationfortestingin

single-celltestequipment(modelFCED-P50;AsiaPaciﬁcFuelCell

Technologies,Ltd.).Theactivecellareawas2×2cm2_._The

tem-peraturesofanode,cell,andcathodeand humidifyinggaswere

allcontrolledataround70◦C.TheﬂowratesofanodeinputH2

andthecathodeinputO2fuelsweresetat100and200mLmin−1,

respectively.TotesttheperformanceofthevariousPt/polyaniline

compositescatalystinMEA,polarizationcurves(I–V)andoutput

powerwereconstructedandrecorded,respectively.

3. Resultsanddiscussion

3.1. Conductivity,surfaceareaandporesizeofPANFandits

partlycarbonizedderivativeascatalystsupport

Theparticle-likeand partly disconnectedmorphologyof the

conductingXC-72 willincrease theresistancefor theproduced

electronstotransporttooutercircuit.Toimprovethe

connectiv-ityoftheconductingelectrocatalystsupport,aPANFisprepared

intheabsenceoforganicsolventfromasimpleemulsiﬁed

poly-merization. The obtained PANF owns higher resistance, bigger

pores, and lower surface areacompared withXC-72 according

toTable1.WhenPANFs arepartlycarbonizedatthehigh tem-peratureof1100◦Cinthenitrogenatmosphere,thesurfacearea signiﬁcantlyrisesmorethanfourtimesfrom40to188m2_g−1_and eventuallythebigporesof241 ˚Abreakintosmalleronesof66 ˚A, whichisalreadysmallerthanthatofXC-72(109 ˚A).Althoughthe hightemperaturetreatmenthascutsomeoftheﬁbersintopieces

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Y.-Z.Wangetal./SyntheticMetals188 (2014) 21–29 29 wt%(18.70%)forcarboxylatedcarbonizedPANF(CPANF-COOH)is

foundtobehigherthanthatofXC-72(17.74%).

CPANF-COOH based electrocatalyst support demonstrates higherelectrochemicalactivitythanXC-72withlargerareacyclic voltammogramsandtheelectrocatalystmadeofcarboxylated car-bonizedPANFsupportrevealsahigherreducingcurrentthanthat ofXC-72intheORR(oxygenreductionreaction).

Thesingle-cellperformancetestingillustratesahigherpower (307mWcm−2)andmaximumcurrentdensity(970.6mAcm−2)for CPANF-COOH,respectively. Besides,theMEAbasedonmodiﬁed PANFcatalystsupportdoesnotexperienceaseriouspowerdensity lossathighcurrentdensitycausedbyconcentrationpolarization.

Thecarbonizationathightemperatureandsubsequent acidiﬁ-cationinstrongacidsforPANFareabletoprepareanoptimized electrocatalyticsupportofPtforbetterPEMFCperformance.The connected1D,N-containing,highlyconductingandanti-water cor-rosionfeaturesmakeCPANF-COOHamorecompetingcandidateas theconductingsupportmediumforaPEMFC.

In thefuture, we willtrytograft various,more hydrophilic groupsontoCPANFsurfacetocapturemorePtionsandobtainhigh Pt-loading%forbetterPEMFCperformance.

References

[1]L.B.Brentner,J. Peccia,J.B. Zimmerman,Environ.Sci. Technol.44(2010) 2243–2254.

[2]D.Das,Int.J.HydrogenEnergy34(2009)7349–7357. [3]B.E.Logan,Environ.Sci.Technol.38(2004)160A–167A.

[4]L.Q.Hoa,E.Tamiya,Y.Sugano,H.Yoshikawa,M.Saito,Electrochim.Acta56 (2011)9875–9882.

[5]D.He,C.Zeng,C.Xu,N.Cheng,H.Li,S.Mu,M.Pan,Langmuir27(2011) 5582–5588.

[6]L.Cindrella,A.M.Kannan,J.PowerSources193(2009)447–453.

[7]M.Michel,F.Ettingshausen,F.Scheiba,Phys.Chem.Chem.Phys.10(2008) 3796–3801.

[8]K.Kinoshita,Carbon:ElectrochemicalandPhysicochemicalProperties,Wiley, NewYork,1988.

[9]K.Kinoshita,J.A.S.Bett,Carbon11(1973)403–411.

[10]S.I.Pyun, E.J.Lee,T.Y. Kim,S.J.Lee,Y.G.Ryu,C.S.Kim,Carbon32(1994) 155–159.

[11]K.-S.Lee,I.-S.Park,Y.-H.Cho,D.-S.Jung,N.Jung,H.-Y.Park,Y.-E.Sung,J.Catal. 258(2008)143–152.

[12]T.Ioroi,Z.Siroma,N.Fujiwara,S.Yamazaki,K.Yasuda,Electrochem.Commun. 7(2005)183–188.

[13]J.Janata,M.Josowicz,Nat.Mater.2(2003)19–24.

[14]A.Malinauskas,J.Malinauskiene,A.Ramanavicius,Nanotechnology16(2005) R51–R62.

[15]G.Li,C.Martinez,S.Semancik,J.Am.Chem.Soc.127(2005)4903–4909. [16]H.Yoon,M.Chang,J.Jang,J.Phys.Chem.B110(2006)14074–14077. [17]A.H.Chen,K.Kamata,M.Nakagama,J.Phys.Chem.B109(2005)18283–

18288.

[18]H.D.Tran,R.B.Kaner,Chem.Commun.37(2006)3915–3917.

[19]O.Osamu,Polyanilinederivativesandtheirproductionprocess,USpatent 5821309.

[20]M.Zhiani,B.Rezaei,J.Jalili,Int.J.HydrogenEnergy35(2010)9298–9305. [21]A.Wolz,S.Zils,M.Michel,C.Roth,J.PowerSources195(2010)8162–8167. [22]Y.F. Huang, C.W. Lin, C.S. Chang, M.J. Ho, Electrochim. Acta 56 (2011)

5679–5685.

[23]B.Qu,Y.Xu,Y.Deng,X.Peng,J.Chen,L.Dai,J.Appl.Polym.Sci.118(2010) 2034–2042.

[24]E.Yli-Rantala,A.Pasanen,P.Kauranen,V.Ruiz,M.Borghei,E.Kauppinen,A. Oyarce,G.Lindbergh,C.Lagergren,M.Darab,S.Sunde,M.Thomassen,S. Ma-Andersen,E.Skou,FuelCells11(2011)715.

[25]N.M.Gavrilov,I.A.Paˇsti,G. Ćiri ć-Marjanovi ć,V.M.Nikoli ć,M.P.M.Kaninski,S.S. Miljani ć,S.V.Mentus,Int.J.Electrochem.Sci.7(2012)6666.

[26]K.S.Ho,Y.K.Han,Y.T.Tuan,Y.J.Huang,Y.Z.Wang,T.H.Ho,T.H.Hsieh,J.J.Lin, S.C.Lin,Synth.Met.159(2009)1202–1209.

[27]S.Mentus,G. Ćiri ć-Marjanovi ć,M.Trchová,J.Stejskal,Nanotechnology20 (2009)245601(10pp.).

[28]N.Gavrilov,M.Daˇsi ć-Tomi ć,I.Paˇsti,G. Ćiri ć-Marjanovi ć,S.Mentus,Mater.Lett. 65(2011)962–965.

[29]Y.J.Wu,K.S.Ho,Y.W.Cheng,L.Chao,T.H.Hsieh,T.H.Ho,Y.K.Han,Polym.Int. 62(2013)581–590.

[30]L.Chao,K.S.Ho,S.Y.Shen,H.Y.Pu,T.H.Hsieh,C.W.Kuo,B.H.Tseng,J.Appl. Polym.Sci.127(2013)1853–1862.

[31]S.Y.Shen,Y.J.Wu,K.S.Ho,T.H.Hsieh,T.H.Ho,Y.Z.Wang,P.H.Tseng,Y.C.Hsu, Polymer52(2011)2609–2617.

[32]B.Z.Hsieh,H.Y.Chuang,L.Chao,Y.J.Li,Y.J.Huang,P.H.Tseng,T.H.Hsieh,K.S. Ho,Polymer49(2008)4218–4225.

[33]E.M.Genies,A. Boyle,M.Lapkowski, C.Tsintavis, Synth.Met.36(1990) 139–182.

[34]M.Zhao,X.Wu,C.Cai,J.Phys.Chem.C113(2009)4987–4996. [35]C.H.Hsu,H.Y.Liao,P.L.Kuo,J.Phys.Chem.C114(2010)7933–7939. [36]T.Maiyalagan,B.Viswanathan,U.V. Varadaraju,Electrochem.Commun. 7

(2005)905–912.