Electroactivity of Pt-Ru-polyaniline composite catalyst-electrodes prepared by electrochemical depos(6)

Fuel Cell

1918S.Kim,S.-J.Park/SolidStateIonics178(2008)1915–1921

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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