Electroactivity of Pt-Ru-polyaniline composite catalyst-electrodes prepared by electrochemical depos

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Available online at

SolidStateIonics178(2008)1915–

1921

/locate/ssi

ElectroactivityofPt–Ru/polyanilinecompositecatalyst-electrodes

preparedbyelectrochemicaldepositionmethods

SeokKima,Soo-JinParkb,

a

AdvancedMaterialsDivision,KoreaResearchInstituteofChemicalTechnology,P.O.Box107,Yuseong,Daejeon305-600,SouthKorea

b

DepartmentofChemistry,InhaUniversity,253,Nam-gu,Incheon402-751,SouthKorea

Received6September2007;receivedinrevisedform17December2007;accepted21December2007

Abstract

TheelectrochemicaldepositionofPt–Runanoparticlesonconductingpolymersupportsandcarbonsupports,aswellastheirelectro-catalyticactivities,wereinvestigated.Pt–Rucatalystsof3–8nmaveragesizeweregrownonsupportsbystep-potentialplatingmethods.Thecatalysts'loadingcontentswereenhancedbyincreasingtheplatingtimeofthedepositionmethod.Polyanilineandcarbonblacks(CBs)wereselectedandcomparedascatalystsupports.TheparticlesizesandmorphologicalstructuresofthePt–Ru/supportcatalystswereevaluatedusingX-raydiffraction(XRD)andtransmissionelectronmicroscopy(TEM).TheelectrochemicalbehaviorsofthePt–Ru/supportcatalystsformethanoloxidationwereinvestigatedaccordingtotheircharacteristiccurrent-voltagecurvesandchronoamperometryinamethanolsolution.Asaresult,theelectrochemicalactivitywasenhancedwithincreasedplatingtime,reachingthemaximumat24min,andthendecreased.Thespecificcurrentdensityforthepolyaniline-supportedcatalystswashigherthanthatfortheCBs-supportedones.Theenhancedcatalyticactivitywasrelatedtothehigherelectricalconductivityofthepolyaniline,theincreasedelectrochemicalsurfaceareaofcatalysts,orthehigheriondiffusionbehaviours.©2008ElsevierB.V.Allrightsreserved.

Keywords:Catalyst-electrodes;Platingmethods;Electroactivity;Supportmaterials;Fuelcells

1.Introduction

Directmethanolfuelcells(DMFCs)areanattractivepor-tablepowersourceowingtotheirhighenergydensity,easyfuelhandling,andalowoperatingtemperature[1–4].However,DMFCsentailsomeserioustechnicalobstacles.Oneistherelativelyslowkineticsofthemethanoloxidationreactionatananode,whichleadstohighover-potentials[5].Platinum(Pt)hasahighactivityformethanoloxidation,andhasbeenusedinanodeelectrocatalystsformanyyears[6–8].However,thePtelectrocatalystwillbepoisonedbyintermediatesofmethanoloxidation,suchasCO.Sincethemid-1970s,topromotemethanolelectro-oxidationbyPt,thecatalystsurfacehasbeenmodifiedbytheadditionofasecondmetaltoPt[9–11].TheresultingPt–Rubinarymetalliccatalystiscommonlyacceptedasthebestelectrocatalystformethanoloxidation[12–15].The

Correspondingauthor.Tel./fax:+82328608438.E-mailaddress:sjpark@inha.ac.kr(S.-J.Park).

0167-2738/$-seefrontmatter©2008ElsevierB.V.Allrightsreserved.doi:10.1016/j.ssi.2007.12.074

otherissueinDMFCsisthemethanolcrossoverfromanodetocathodeacrossthemembrane.Itiswellknownthatmethanolcrossoverlowersfuelutilizationandcausescathodeover-potential[16–19].

Pt–Rucatalystscanbepreparedbyanelectrochemicalplatingmethodaswellasaconventionalchemical-reductionmethod[20–22].Recently,electrochemicaldepositionofmetalcatalystshasbeenreceivingmoreandmoreattentionduetoadvantagessuchasitshighpurityofdeposits,simpledepositionprocess,andeasycontroloftheloadingmass.Byapplyingaspecificcurrentforashorttime,andthenrepeatingtheprocessduringelectrodeposition,eachcycleofthisprocesscangeneratenewmetalparticles[23].Therefore,bycontrollingthemag-nitudeofthecurrentorpotential,nanoparticlescanbealteredinsizeandstructure[24].Beside,thedevelopmentofasup-portmaterialisessentialtominimizingnoblemetalloadingandachievingoptimumcatalyticperformance[25–30].Carbonmaterialsarewidelyusedassupportmaterials.Althoughcarbonblacks(CBs)arethemostcommerciallyusedcarbonsupportmaterials,differentkindsofcarbonnanotubes,graphiticcarbon

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nanofibers,andorderedmesoporouscarbonshaverecentlybeeninvestigated[31–34].

Thesizeandloadingcontentofcatalystparticlesonthesubstratedeterminethecatalysts'performanceasanelectrodematerial.Ithasbeenreportedthataneffectivedispersionofcatalystparticlescausesadecreaseinsurfacepoisoning.Dif-ferentsubstratesforcatalystparticleshavebeentried,withtheaimofimprovingtheefficiencyofmethanolelectro-oxidation.Conductingpolymerscanbeusedassuitablehostmatricesfordispersingmetallicparticles.Conductingpolymer/metal-nano-particlescompositespermitafacileflowofelectronicchargesthroughthepolymermatrixduringtheelectrochemicalprocess.Additionally,electricalconductingpolymersprovidealowohmicdropofelectrontransferbetweenthemetalcatalystandthesubstrates.Also,metallicparticlescanbedispersedintothematrixofthesepolymers.Bycombiningconductingpolymersandmetalparticles,itisexpectedthatnovelelectrodeswithhigherspecificsurfaceareasandenhancedelectrocatalyticac-tivitiescouldbeprepared.

Recently,Y.E.Sungetal.proposedthatPt–Runanoparti-cles/electricalconductingpolymernanocompositesareeffectiveasanodecatalysts[35].Atthattime,theelectricalconductivityofpolymerswasrelativelylowcomparedwithamorphouscar-bon,andsyntheticmethodswerelimitedtoelectrochemicalpolymerizationfromnonaqueoussystems.Inpreviousstudies[36,37],metalparticlescouldbehomogeneouslydispersedonpolyanilinefilmbyconstantpotentialelectro-platingtechni-ques.However,inourstudy,step-potentialplatingmethodswereutilizedtoobtainasmallersizeandabetterelectrochem-icalactivity.

Theaimofthisstudywasnotonlytoimproveanelectricalconductivityandaneffectivesurfaceareaofcatalystelectrodesusingelectricalconductivity-enhancedpolyanilineasacatalystsupport,butalsotocontrolthesizeandloadinglevelofPt–Ruparticlesbythesteppotentialplatingmethod.Itisexpectedthatwell-dispersedcatalystsonconductingpolymerscanleadtobetterPtutilizationandanimprovementofthecatalyticactivityinmethanoloxidation.2.Experimental2.1.Supportmaterials

CBsandpolyanilinewereusedasasupportforthemetalcatalysts.TheCBsof24nmaverage 1particlesize,andhavingaDBPadsorptionof153(cc-100g)andaspecificsurfaceareaof112(m2g 1),weresuppliedbyKoreaCarbonBlackCo.Polyanilinepowderwassynthesizedchemicallybyoxidativepolymerizationofanilineinanaqueousacidicsolution[38–40].Theaniline(8.4g,0.09mol;Aldrich),distilledthreetimesbeforeuse,wasdissolvedin300mLofaqueoussolutioncontaining0.09moldodecylbenzenesulfonicacid(DBSA)below5°C,andanaqueoussolution(100mL)of0.06molammoniumperoxydisulfate,(NH4)2S2O8,wasaddedwithvigorousstirring,overaperiodof30min.Themixturewasstirredcontinuouslyfor24h.Theprecipitatewascollectedafterpouringmethanolandbyfiltration,andthenwashedwithwaterandmethanolthreetimes.

Theresultingpowderwasdriedunderadynamicvacuumat40°Cfor2days.TheDBSA-dopedpolyanilinewasconfirmedbymeasuringtheelectricalconductivity(~80S/cm).Theconduc-tivityofCBswas0.7S/cm.PANIandCBspellets,fabricatedbycompressing7PANIandCBspowderunderthepressureof5.0×10kg/m2atroomtemperature,weremeasuredforcon-ductivityusingthefour-probemethod.

2.2.ElectrodepositionofPt–RunanoparticlesonsupportElectrodepositionofPt–RunanoparticlesonsupportwasinvestigatedusinganAutolabwithaPGSTAT30electroche-micalanalysisinstrument(EcoChemieB.V.;Netherlands).Thesolidprecursorschloroplatinicacid(H2PtCl4,Aldrich)andrutheniumchloride(RuCl3,Aldrich)wereusedwithoutpuri-fication.Astandardthree-electrodecellwasemployed.Thesupportmaterialsmixedwith10%NafionPerfluorosulfonatedion-exchangeresin(Aldrich)solutionwasdroppedontotheglassycarbonelectrodeasaworkingelectrode.APtwireasthecounterelectrodeandKCl-saturatedAg/AgClasthereferenceelectrodewereused,respectively.Pt–Runanoparticleswere,bysteppotentialplatingmethod,electrodepositedontheCBandpolyanilinecatalystelectrodesfromdistilledwatersolutioncontainingrutheniumchlorideandchloroplatinicacid.Inthedepositionsolution,theconcentrationofPtandRuwas20mM.Apotentialfunctiongeneratorwasusedtocontrolboththesteppotentialvalueandtheintervaltime.ThepotentialwaveformofthedepositionisshowninFig.1.Thecatalystswerecycledintherangeof 0.3Vto 0.8V(V1andV2)withanintervaltime(t1andt2)of0.1s.Theelectrocatalystswerepreparedbychangingtheplatingtime.

2.3.Physicalmeasurements

Transmissionelectronmicrographs(TEM)ofthecatalystsamplesweretakenusinga200,000×magnification

transmission

Fig.1.Step-potentialplatingmethodshowingparametersofappliedpotentialandintervaltime.

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Fig.2.X-raydiffractionpatternsofPt–Ru/CBscatalystspreparedfordifferentplatingtimesof(a)6,(b)12,(c)24,and(d)36

min.

electronmicroscopewithaspatialresolutionof1nm.Beforetakingtheelectronmicrographs,thecatalystsampleswereultrasonicallydispersedinisopropylalcohol,andadropoftheresultantdispersionwasdepositedanddriedonastandardcopper-gridcoatedwithapolymerfilm.Theappliedvoltagewas100kVforthecatalysts.

AnXRDanalysiswascarriedoutonthecatalyststhatwerepreparedfromdifferentconditions,bymeansofaRigakuD/MAX-ШBX-RaydiffractometerusingaCuKαsourceoper-atingat45kVand100mA.1TheXRDpatternswereplottedatascanningrateof4°min withanangularresolutionof0.05°for2θscans.X-raydiffractogramswereobtainedfor2θvaluesvaryingbetween30°and85°.TheaveragecrystallinesizesoftheparticlesweredeterminedfromtheX-raydffractograms,usingtheScherrerEq.(1)[41].L¼

0:9k

B2hcoshmax

ð1Þ

whereλistheX-raywavelength(1.54056ÅfortheCuKαradiation),B2θisthewidthofthediffractionpeakathalf-height,andθmaxistheangleatthepeakmaximumposition.

Fig.3.X-raydiffractionpatternsofPt–Ru/polyanilinecatalystspreparedfordifferentplatingtimesof(a)6,(b)12,(c)24,and(d)36min.

Table1

MeansizeandloadingcontentsofPt–Ru/CBscatalystsPlatingtimeCrystallinesizeParticlesizePtRuAlloyedRu(min)(nm)a(nm)b(wt.%)c(wt.%)c(%)6–

8.12.11.021125.2±0.35.43.91.224243.4±0.23.66.12.13236

4.2±0.2

4.6

7.2

3.1

26

aMeasuredfromXRDresults.b

MeasuredfromTEMresults.c

MeasuredfromICP-AESresults.

TheloadingmassofthePt–RuwasdeterminedbyInductivelyCoupledPlasma-AtomicEmissionSpectroscopy(ICP-AES)usingaJobinYvonUltima-CSpectrometer.2.4.Electrochemicalmeasurements

Electrochemicalmeasurementswerecarriedoutinaconven-tionalthree-electrodeelectrochemicalcellat25°C.ApieceofPtwirewasusedasthecounterelectrode,andKCl-saturatedAg/AgClwasusedasthereferenceelectrode.Theglassycarbonelectrode,asaworkingelectrode,wascoveredwithcatalystpowder.Allofthesolutionswerepreparedwithultra-purewater.Asolutionof1MCH3OHand0.5MH2SO4wasstirredconstantlyandpurgedwithultra-pureargongas.Electroche-micalexperimentswereperformedusinganAutolabwithaPGSTAT30(EcoChemieB.V.;Netherlands).3.Resultsanddiscussion

3.1.Sizeandloadinglevelofcatalysts

ThecrystallinestructuresofthePt–Ru/CBsandPt–Ru/polyanilinecatalystswereinvestigatedbyX-raydiffraction(XRD).Figs.2and3showtheXRDpatternsofthecatalystspreparedbychangingtheplatingtimeofthestep-potentialplatingmethod.Thepeaksat2θ=40°,47°,68°,and82°wereassociatedwiththe(111),(200),(220),and(311)typesre-spectively.AllofthecatalystsdemonstrateddiffractionpatternssimilartothoseofthePt.ThecharacteristicpeaksforRuwerenotclearlyshownintheXRDpatterns.Inthecaseofthe6minplatingtime,thecharacteristicpeaksofPtwerenotdistinct,indicatinginefficientelectrodepositionofthemetalcatalysts.Forthe12minplatingtime,Pt(111)appearedat~40°.

After

Table2

MeansizeandloadingcontentsofPt–Ru/polyanilinecatalystsPlatingtimeCrystallinesizeParticlesize

PtRuAlloyedRu

(min)(nm)a(nm)b(wt.%)c(wt.%)c

(%)6–

7.42.31.320124.3±0.34.57.63.125242.9±0.23.19.34.63536

3.9±0.3

4.2

11.1

5.3

27

a

MeasuredfromXRDresults.b

MeasuredfromTEMresults.c

MeasuredfromICP-AESresults.

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Fig.4.TEMmicrographofPt–Ru/CBscatalystsby(a)6min,(b)12min,and(c)24minplating

time.

24minplating,thecatalystsshoweddefiniteandenhancedpeakintensityforthefourkindsofpeaks.Inthecaseof36minplating,thecatalystsclearlyshowedthecharacteristicpeaks.ThepreciseloadingcontentsofthecatalystswereobtainedbyusingICP-AESmethods,andaregiveninTable1.TheloadingcontentofPtwasupgradedfrom2.1%to7.2%,andthatofRuwaschangedfrom1.0%to3.1%.Theloadingcontenthadbeenincreasedproportionallyasafunctionofplatingtime.

SimilartotheFig.2results,andasshowninFig.3,thecrystallinepeaksofthepolyaniline-supportedcatalystswerenotclearlyevidentfortheinitialplatingtimeof6min,exceptfortheappearanceofasmallPt(111)peak.After12minplating,thecatalystsshowedthefourcharacteristicpeaks.Within-creasingplatingtimeafter24min,thepeaksbecamesharpanddefinite.

Consideringparticlecrystallinesize,theaveragesizesofCBs-supportedcatalystsshowedthesmallestvalue,3.4nm,at24minplating,asshowninTable1.Beside,particlesizesbyTEMresultswereshowninTables1and2.Inthecaseof6minplatingtime,theaveragesizewas~8nm.Itwasconsideredthatparticlenucleationwasnotasefficientastheparticlegrowthattheinitialstageofelectrodeposition.After24minplating,theparticlenucleationwasefficientenoughtoproduceanew

generationofsmallparticles,resultinginthedecreaseoftheaveragecrystallinesize.AlthoughmoreprecisenucleationandgrowthmechanismsarenecessaryforPt–Runanoparticles,itwasfoundthatthesmallercrystallinesizecouldbeobtainedafteraninitialactivationstate.Thisbehaviorwasalsoobservedinthecaseofpolyanilinesupports,asshowninTable2.Regardlessofthesupportmaterials,thesmallestnanoparticleswereobtainedbyelectrodepositionafter24minplatingtime.TheloadingcontentofPtorRuwas11.1%or5.3%,respec-tively,after36minplatingtime.ThesevalueswereslightlyhigherthatthoseoftheCBssupports.Itwasconcludedthatconductingpolymersupportsaremorebeneficialforahigherloadingforelectrodepositionofcatalysts.

ThepeakpositionofPtRucatalystshadbeenshiftedincomparisonwiththatofpurePtcatalyst.Theshiftofpeakpositioncouldmeanthechangeofalatticeparameter.

Wehadcalculatedthealloyingdegreebythefollowingformula[42];

lPtRu¼0:3916À0:124xRu

ð2Þ

(wherelPtRuisthelatticeparameterofPtRucatalysts,andxRuisthepercentofRuinthealloy).Thelatticparameter

of

Fig.5.TEMmicrographofPt–Ru/polyanilinecatalystsby(a)6min,(b)12min,and(c)24minplatingtime.

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PtRuissmallerthanthatofPt,meaningapartofRuhadenteredintothecrystallatticeofPt.ThealloyingdegreeofRuhadbeeninsertedinTables1and2.

TheparticlesizesandmorphologiesofthePt–Ru/CBsandPt–Ru/polyanilinecatalystswereinvestigatedbyTEM.Fig.4showsaTEMimageofnanoparticlecatalyststhatwerepreparedonCBsbyelectrodepositionwithplatingtime.24minplatingshowedthesmallestparticlesizes.Thisshowsthenanoparticlesinthe2.5–5.0nmsizerange.Fig.5showsaTEMimageofcatalyststhatwerepreparedonpolyanilinesupportswithchangingplatingtime.24minplatingshowsnanoclusterswithindividualparticlesof2.5–4.1nmsize.TheaveragecrystallinesizescalculatedfromtheXRDpeakwidthswerefoundtobefairlyconsistentwiththosefromtheTEMresults,asshowninTables1and2.

3.2.Electrochemicalpropertiesofcatalysts

Theelectrochemicalpropertiesofthecatalystswereinves-tigatedbycyclicvoltammetryin1MCH3OH+0.5MH2SO4aqueoussolution.Fig.6showstherepresentativecurrent–voltagecurvesoftheCBs-supportedcatalysts,presentingtheelectrochemicalbehaviorofmethanoloxidation.VoltammetricbehaviordependsonthePtcontent.Theelectrochemicalactivityincreasedwithincreasingplatingtime,reachingthemaximumat24min,andthenslightlydecreased.However,thecatalystsshowedanincreasedPtcontentwithplatingtimeto36min.Theoptimalplatingtimewas24min,althoughthePtcontentwasthehighestwhentheplatingtimewas36min.Thecatalystby24minplatingshowedthehighestcurrentdensityformethanoloxidation,indicatingthehighestelectroactivitybyanenhancedspecificsurfaceareaofareactionsiteformetalliccatalysts.Thisresultwasconsideredtohavebeenoriginatedfromthecatalyst'ssmallerparticlesizeandloweraggregation.

Inthecaseofthepolyaniline-supportedcatalysts,thecyclicvoltammogramsshowninFig.7alsoexhibitmethanoloxi-dationpeak.ThecatalystdepositedonPANIshowedaratherdefiniteoxidationpeakat~520mV.SimilartotheCBssup-ports,thecatalystsshowedthehighestelectroactivityat24min

Fig.6.CyclicvoltammogramsofPt–Ru/CBscatalystspreparedfordifferentplatingtimesof(a)6,(b)12,(c)24,and(d)36minin1Mmethanolsolution(scanrate:20

mV/s).

Fig.7.CyclicvoltammogramsofPt–Ru/polyanilinecatalystspreparedfordifferentplatingtimesof(a)6,(b)12,(c)24,and(d)36minin1Mmethanolsolution(scanrate:20

mV/s).

plating.Indeed,thecatalystsby24minplatingexhibitedanaveragesizeof3.1nm,whereasthecatalystsby36minplatingshowedanaveragesizeof4.2nm.Smallerparticlesofcatalystsmightresultinalargeavailablecatalystsurfaceareaandgoodelectrocatalyticpropertiesformethanoloxidation.

TodeterminethecarbonandPANIsupportinfluences,in-dividually,ontheoxidationcurrentofcatalysts,supportswith-outmetalcatalystswerestudiedin1MCH3OH+0.5MH2SO4aqueoussolution,asshowninFig.8.Thecarbonsupportdidnotshowanyelectrochemicalactivityexceptforsomesmallcapacitivecurrent.Bycontrast,thePANIsupportshowedadefinitecathodic/anodicpeak,indicatinganoxidation/reductionreaction[38–40].However,itwasconcludedthatpolyanilinesupportscouldnotfunctionaloneascatalystsformethanoloxidation.

Tocheckthespecificsurfaceareaofcatalysts,cyclicvol-tammograms(CVs)hadbeenperformed.Fig.9showstheCVsofthePANI-orCBs-supportedcatalystsin1.0Msulphuricacidsolution.H2adsorption/desorptionpeakwereobservedat 200mVforbothcaseandtheelectrochemicalsurfaceareaarecalculated(PtRu/PANI:4.3cm2,PtRu/CBs:7.4cm2).

By

Fig.8.Cyclicvoltammogramsof(a)CBsand(b)polyanilinesupportsin1Mmethanolsolution(scanrate:20mV/s).

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Fig.9.Cyclicvoltammogramsof(a)Pt–Ru/CBsand(b)Pt–Ru/polyanilinepreparedby24minplatingin1Msulfuricacidsolution(scanrate:20

mV/s).

consideringthedifferentmetalloading,weobtainedthespecificsurfaceareabydividing2themetalweight(PtRu/PANI:62m2/g,PtRu/CBs:75m/g).CatalystdepositedonPANIshowedthehigherspecificsurfaceareathanPtRu/CBs.Thisresultsup-portedthattheeffectivesurfaceareacouldbedependentontheparticlesizeandaggregationdegree.

Beside,chronoamperometrycouldbeusedtoobtaintheap-parentdiffusioncoefficientofionsinelectrochemicalreactions.ThecurrentresponseswithtimewereshowninFig.10.Afterthepotentialwasraisedabruptlyfrom 0.2to0.6V,ingafollowingequation,theapparentdiffusioncoefficienthadbeencalculated[42,43]. lni i¼Àp2Dtð3Þ

Ol

whereioistheinitialcurrent,ithecurrent,lsamplethicknessandtthetime.

Theobtaineddiffusioncoefficientswerelikefollowing;PtRu/PANI:6.1×10 9cm/s,PtRu/CBs:4.2×10 9cm/s.Theformercasewasahighervaluethanthelattercase.Thisresultcouldbeoneofthereasonsoftheimprovedelectroactivity.

Fig.10.Chronoamperometryresultsof(a)Pt–Ru/CBsand(b)Pt–Ru/polyanilineby24minplatingin1Mmethanol

solution.

Fig.11.Specificcurrentdensityforoxidationpeaksof(a)Pt–Ru/CBsand(b)Pt–Ru/polyanilinecatalystspreparedfordifferentplatingtimes((c)CBsand(d)polyanilinesupportsthemselveswereaddedforcomparison)(at600mV).

Fig.11showsthespecificcurrentdensitiesofthepreparedPt–Ru/CBsandPt–Ru/polyanilinecatalysts.Thecurrentden-sitiesofthedifferentmaterials-supportedcatalystsasafunctionofplatingtimeshowedsimilarbehaviours.ThePANI-supportedcatalystsshowedenhancedelectroactivitycomparedwiththecarbon-supportedcatalysts.Intheearlystageof6minplating,thedifferenceofenhancedcurrentdensity(41 9=32(mA/mg))wasalmostsimilartothecurrentdensity(27(mA/mg))ofPANIitself.However,inthecaseof24minplating,thedif-ferenceofincreasedcurrentdensity(121 68=53(mA/mg))wasmuchhigherthanthecurrentdensityofPANIitself.Ac-cordingly,itwasconcludedthattheimprovedelectroactivityofthePANI-supportedcatalystswasaresultnotonlyofthecombinedactivityofthecatalystsandthePANI;oneofthemainsourcesoftheimprovedelectroactivitywasthehighelectronicconductivityofDBSA-dopedpolyaniline(~80S/cm)comparedwiththatoftheCBs(~0.7S/cm)[44].Additionally,wehadfoundthattheelectrochemicalareaofcatalystshadbeenincreased.Theincreasedelectrochemicalareamightberelatedtothesmallparticlesizeandlowdegreeofaggregation.4.Conclusions

Inthepresentstudy,thepreparationandcharacterizationofPt–Ru/CBsandPt–Ru/polyanilinecatalystswereinvestigated.Pt–Ruparticleswere,bystep-potentialplatingmethods,electro-depositedontoCBsandpolyanilinefromdistilledwatersolutioncontainingrutheniumchlorideandchloroplatinicacid.Thepar-ticlesizesofthePt–Rucatalystswereabout3–8nm.Fromtheloadingcontentresultsasafunctionofplatingtime,theefficiencyofloadingwasenhancedtoN11wt.%withtheincreaseoftheplatingtimeto36min.However,fromtheviewpointofaverageparticlesizes,thesmallestnanoparticlesof3.1nmwereobtainedbyelectrodepositionwith24minplatingtime.

Theelectrochemicalactivityincreasedwithincreasingplatingtime,toamaximumof24min,andthendecreased.Theseelec-troactivitychangesasafunctionofplatingtimewereinverselyproportionaltothesizeofthenanoparticlescatalysts,indicatingthatthehigherelectroactivitycouldhavebeenenabledby

the

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decreasingaveragesizeofnanoparticlecatalysts.H2adsorption/desorptionresultsshowedthatPtRu/PANIhadthehigherspecificsurfaceareaforanelectrochemicalreactionthanPtRu/CBs(75N62m2/g).ChronoamperometryresultsindicatedthatPANIsupportsshowedthe9higherapparentiondiffusioncoefficientthanCBs(6.1×10 N4.2×10 9cm/s).Themethanoloxida-tionspecificcurrent(121(mA/mg))forpolyaniline-supportedPt–Rucatalystswashigherthanthat(68(mA/mg))forCBs-supportedPt–Rucatalysts.Theenhancedspecificcurrentdensityofpolyaniline-supportedPt–Runanocompositeswasattributedtotherelativelyhigherelectricalconductivityofthepolyanilineortheincreasedelectrochemicalarea,whichcouldberelatedtothesmallparticlesizeandlowdegreeofaggregation.References

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