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

Fuel Cell

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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