Carbon nanosheet正式稿

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Citethis:RSCAdv.,2016,6,75178

GrowthofcarbonnanoshellsontungstencarbideforloadingPtwithenhancedelectrocatalyticactivityandstableanti-poisoningperformance?

BaoJunHan,aZhiJuanHuang,aGaoWu,bCaiYingZhou,bYeShengLi,*bQingHuiWang,bYuLongZhang,cYanHongYinbandZiPingWu*b

Carbonnanoshells(CNS),with3to8nearlytransparentlayersprecipitatedonWCparticles,havebeenpreparedbyaninsitudeoxidizationapproach.Becausethedecompositionofcarbonatomsfromthecarbonsourcecanbemediatedbymethanol,WO3canbefullydeoxidized.WhentheremainingcarbonatomsimmigrateintotheformedWCatthereactiontemperatureandemigrateoutoftheWCat

Received13thMay2016Accepted27thJuly2016DOI:10.1039/c6ra12475em.kkreddy.com;wuziping724@jxust.edu.cn

SchoolofMaterialsScienceandEngineering,GuilinUniversityofTechnology,12JianganRoad,Guilin541004,P.R.China

?Electronicsupplementary10.1039/c6ra12475e

information(ESI)available.SeeDOI:

carbonoenmixeswiththecarbidephasesinpreparedsamples.11–15ThePt-likebehaviorandsynergistice?ectbetweencarbidesandnoblemetalsincreaseastheparticlesizeofWCdecreases.16Whethersurfacecarbonhasanegativeorapositivee?ectonthecatalyticactivityofWCremainsunclear.Haraetal.reportedthatsurfacecarbonhasanegativee?ectonthecata-lyticactivityofhydrogenoxidation.17Chenetal.reportedthatsurfacecarbononorderedmacroporousWChasapositivee?ectonmethanoloxidationactivity.18Thinlayersofsurfacecarbondonotadverselya?ectthecatalyticactivityofWC,whereasthicklayersofsurfacecarbonsignicantlydecreaseitscatalyticactivity.14AlthoughenhancedhydrogenevolutionhasbeenachievedbymixingreducedgrapheneoxideandWC,athincarbonlayerofsurfacecarbonhasnotyetbeenpreparedinWCbecauseitrequiresacomplexpreparationmethod.19,20

Metallicsubstrateshavebeenanimportantfactorinpreparinggraphenesincetheemergenceofchemicalvapordeposition(CVD).Copperandnickelareidealsubstratesforlowcarbonsolubilityathightemperature.21,22Ethanolcanbesup-pressedbymethanolasamediatorathightemperaturebecauseofthedecompositionofacarbonsource,suchasN-hexane.23Inthepresentstudy,ethanolmixedwithmethanolwaspumpedintoareactionfurnacetocarbonizetungstenoxide(WO3)andcarbonnanoshells(CNS)self-generatedonthesurfaceofpreparedWC.Tothebestofourknowledge,WCasasubstratehasnotbeenstudiedforgrowingCNSsimilartographene.24–29WhenPt(10wt%)accumulatedontheWCwiththesurfacecarbonofself-generatedCNSasacarrier,theobtained(WC–CNS)/Ptcompositedisplayedsignicantlyincreasedelectro-chemicalactivity.Moreover,thestableanti-poisoningperfor-manceoftheelectrocatalystdidnotchange.

75178|RSCAdv.,2016,6,75178–75185Thisjournalis?TheRoyalSocietyofChemistry2016

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2.1

Experimental

Preparationoftungstenoxide(WO3)

2.5Electrochemicalmeasurements

y on 30/08/2016 03:37:21.

Atotalof0.1mgmlà1ofhomogeneousdouble-walledcarbonnanotubes(DWCNT)/ethyleneglycol(EG)suspensionwaspreparedinaccordancewithapreviousreport.30Approximately3.96gofsodiumtungstate(Na2WO4)wasaddedto100mlofDWCNT/EGsuspension.Thecomplexsuspensionwastrans-ferredintoaround-bottomedask,and8mlofHClwasaddedtothesuspensionandmaintainedfor4h.Thecomplexsuspensionwassubsequentlyheatedto100??Cinareuxdevice.Theas-receivedsamplewascooledtoroomtemperature,TheelectrochemicalactivitiesoftheWC–CNScompositewerecharacterizedwithcyclicvoltammetry(CV).Experimentswereperformedinathree-electrodecellusinganEG&Gpotentiostat(CHI618C)atroomtemperature.Workingelectrodeswerepreparedbyspreadingacatalystcoatingand5%Naonmixtureinethanolonaglasscarboncylinderwithadiameterof3mm.ThePtloadingoftheworkingelectrodewascontrolledat0.2mgcmà2.APtfoilandsaturatedcalomelelectrode(SCE)wereusedasthecounterelectrodeandelectrolyte,respectively.ThemethanolelectrooxidationactivitywasmeasuredinamixedN2-saturatedsolutionthatcontained1MCH3OHand0.5MH2SO4.ltered,washedwithexcessdeionizedwater,anddriedatroomtemperatureinalow-vacuumsystem.Aerwards,thereceivedsamplewasplacedinaheatedfurnace(600??C)withairpumpedataowrateof300mlminà1for1h.Aerthefurnacewascooledtoroomtemperature,thereceivedproductswerecollectedfromthefurnace.2.2

InsitugrowthofCNSonWC

Thepreparedtungstenprecursorwasplacedinafurnace,andtwoangeswereappliedonbothendsofthereactiontubetosealthereactionchamber.Aerthesystemwasheatedto950??

C,ethanolandmethanolwithavolumeratioof10:90weresuppliedtothereactorviaanelectronicsquirmingpumpalongwithahigh-puritynitrogenowfor1hwithsupplyandowratesof3mlhà1and300mlminà1,respectively.Thefurnacewasturnedo?andcooledtoroomtemperatureaer3h.Thereceivedproductswerecollectedfromthefurnace.Toremovethedepositedcarbononthesurfaceofthepreparedsamples,high-purityhydrogen(owrate:30mlminà1)andnitrogen(owrate:300mlminà1)weremixedandthensuppliedtothereactorfor1haerthetungstenprecursorwascarbonized.2.3

PtdepositiononWC–CNS

Measuredchloroplatinicacid(H2PtCl6)wasaddedtotheEGsolutionandthenheatedto140??Cinareuxdevicefor5h.Aertheas-receivedsamplewascooledtoroomtemperature,itwasltered,washedwithexcessdeionizedwater,anddriedatroomtemperatureinalow-vacuumsystem.Ptloadingwascontrolledat10wt%.2.4

Characterizationofsamples

Themicrostructuresofthesampleswerestudiedusinghigh-resolutiontransmissionelectronmicroscopy(HRTEM,JEOL2100F,acceleratingvoltage200kV)andeldemissionscanningelectronmicroscopy(SEM,ZeissSupra55Sapphire).Then,energydispersiveX-rayspectroscopy(EDS)wasusedtoanalyzethechemicalcompositionsofselectedareas.Thecrystalstruc-tureswereanalyzedbyX-raydi?raction(XRD,D8Advance,Bruker)usingCuKaradiation,andRamanspectroscopywasperformedtoexaminethepropertiesoftheCNSandWCusingaHoribaJobinYvonHR800UVwitha514.5nmexcitationwavelengthlaser.

Thisjournalis?TheRoyalSocietyofChemistry2016TheCVproleswererecordedatascanrateof100mVsà1forpotentialsagainstSCErangingfromà0.3Vto0.999V.

3.Resultsanddiscussion

Ourgrouprecentlypreparedtungsticacid(H2WO4)andWCnanosheetswithahighsurfaceareausinganinsituDWCNTtemplate.6ThemolarratioofthetungstenprecursorandDWCNTs(W:C)wasincreasedtoapproximately15:1basedonourpreviousresults.ThemicrostructuresofthepreparedH2WO4aerheatingwereexaminedusingSEMandHRTEM.ESIFig.S1?depictsthemorphologyoftheas-preparedH2WO4.Su?cientsupportcouldnotbeprovidedbecausealargenumberofH2WO4crystalseedswerepreparedanddepositedonasmallnumberofDWCNTbundles.Therefore,thesheetmorphologyofH2WO4showninourpreviousstudywastrans-formedintosphericalparticles.ThisresultindicatedthattheDWCNTsinthesolutionsignicantlyinuencedthesizesandmorphologiesofthedepositedsamplesbasedonthereactionofNa2WO4andHCl.Moreover,theWO3samplecouldbeobtainedaertheH2WO4washeated.Fig.1ashowsthathomogeneousparticlesofthesampleconglomerated,andmostoftheseparticleshadadiameteroflessthan50nm.ThemorphologiesofthesampleswerealsoinvestigatedviaHRTEM.Largequan-titiesofnanoparticlesareshowninFig.1b.Sphericalparticleswithadiameterofapproximately50nmwereobservedwhenthemorphologyofthesamplewasmagnied(Fig.1c).TheseresultsindicatedthatthemorphologyoftheheatedH2WO4wascorrelatedwiththatofH2WO4beforeheating.ThelatticefringesdisplayedinFig.1dindicatedthattheobtainedsamplehasahighlycrystallinestructure,andthelatticespacingof0.37nmcorrespondedtothe(200)interplanardistanceofWO3,therebyindicatingtheoccurrenceoftheH2WO4/WO3+H2Oreaction.

Fig.2showsthemorphologyoftheWO3sampleaercarbonizationwithethanolandmethanolsolutioninasealedreactionchamberwithnitrogenatmosphere.Theimagesdis-playedthepresenceoftwostructures:therstimageshowsparticleswithadiameterofapproximately100to200nmthatareconglomeratedwithoneanother,andtheotherimagevaguelyshowsthinshellsofprecipitationontheseparticles,particularlyintheselectedareashowninFig.2a.NearlytransparentshellscouldbeobservedclearlywhentheselectedareawasmagniedinFig.2b.Thecompositesampleswere

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Carbon nanosheet正式稿

images.

Fig.2ThemorphologyoftheWO3aftercarbonization:SEM(aandb)andTEM(candd)images.

furthercharacterizedthroughTEM.AsshowninFig.2c,the

largeparticlesconglomeratedwitheachother,andtheir

diametercannotbeevaluatedeasily.However,alargequantityofnanosheetsornanoshellswithawidthofapproximately100nmandlowthicknesscanbereadilyobserved.TheimageofthecompositeinFig.2dalsoindicatedthatthesamplehasa

Carbon nanosheet正式稿

sheet75180|RSCAdv.,2016,6,75178–75185Thisjournalis?TheRoyalSocietyofChemistry2016

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Withfurtherinternaldi?usionoftheformedcarbonatomsintoWO3(Fig.4dande),WxC(x>1)canbeobtainedbecauseinsu?cientcarbonatomsareprovided.SimilartotheresultsshowninFig.3b,W2Cphasewasobservedintheobtainedsamples.TheXRDdataindicatedthattheWO3sampleswerenotcarbonizedcompletelyat900??C,andtheresultscorre-spondedtotheSEMimagesshowninESIFig.S2.?Mostlyhomogeneousparticleswithdiametersoflessthan100nmcanbeobtainedatacarbonizationtemperatureof900??C,withalatticespacingof0.19nm,whichcorrespondstothe(101)interplanardistanceofWC.However,theW2Cphase(latticespacingof0.23nmthatcorrespondstothe(102)interplanardistanceofWC)canalsobeobservedinESIFig.S2b.?There-Fig.3XRDpatternsoftheas-preparedWO3beforecarbonization(a)andaftercarbonizationat900??C(b)and950??C

Carbon nanosheet正式稿

(c).

orshellstructure,andthewidthofthesampleisnearly100nm.Therefore,ashellstructure(notcageorsphericalstructures)withverylowthicknesswasobtainedaertheprecursorwascarbonizedaccordingtotheSEMandTEMresults.

ToclarifythecarbonizationprocessofWO3,samplesbeforeandaercarbonizationat950??CwereanalyzedusingXRDbasedonourpreviousthermoanalysisresults.6Fig.3ashowsthedi?ractionpeaksof2q?24.1??,28.1??,33.3??,35.8??,41.5??,48.4??,and54.8??,whichwereindexedastheplanesof(200),(111),(021),(121),(221),(040),and(240)forWO3,respectively.ThelatticespacingshowninFig.1disalsoconsistentwiththeXRDdata.Alowcarbonizationtemperatureof900??CwasusedtoobtainWCparticleswithsmalldiameters.Moreover,theWCphasecanbeobservedintheXRDpattern,asshowninFig.3b.TheseresultsdemonstratedthatthecarbonsourceofethanolandmethanolsolutioncoulddecomposeandformcarbonatomsneartheWO3at900??C.Whenthecarbonatomsdi?usetothesurfaceofWO3(Fig.4aandb),thenearbyWO3canbecarbonizedintoWCwhensu?cientcarbonatomsareprovided.

Fig.4Schematicofthemigrationrouteofcarbonatomsdecom-posedfromethanolonthesurfaceorinteriorofWO3or

Carbon nanosheet正式稿

WC.Thisjournalis?TheRoyalSocietyofChemistry20162fore,theWCandW2CphasescanbeobtainedaerWO3iscarbonizedat900??C(thesamplewasnamedWC–W2C).Alargenumberofcarbonsourcescandecompose,andtheformedcarbonatomscanmigratequicklywhenthecarbonizationtemperatureisincreasedto950??C.Therefore,afullcarbon-izationreactionwouldoccurwhenasu?cientnumberofcarbonatomsdi?usedfromthesurfacetowithintheWO3.Fig.3cshowsevidentcharacteristicpeaksat2q?31.5??,35.7??,48.4??,64.1??,73.3??,77.3??,and84.3??,whichwereindexedasthe(001),(100),(101),(110),(111),(102),and(201)planesofWC,respectively.Therefore,thesamplecanbeinferredtobeWC.TheseresultsindicatedthatWO3canbefullycarbonizedat950??

C.Theaboveresultsindicatethatthecarbonizedreactionmayconsistoftwoprocesses.TherstprocessisthecarbonizationofWO3intoWxC(x>1),andthesecondisthefurthercarbon-izationofWxC(x>1)intoWC,giventhepresenceofasu?cientnumberofcarbonatomswithmobilityaroundtheWxC(x>1).ThecarbonizedsamplewasusedtofurtherinvestigatetheWCparticleswithananoshellstructurethroughRamanspectra.TheresultinFig.5arevealsthatthecharacteristicpeaksat127,267,331,715,and805cmà1areconsistentwiththoseofcommercialWC,showninFig.5c.31Thecharacteristicpeaksat1327cmà1and1585cmà1(abroadpeakcanalso

Carbon nanosheet正式稿

Fig.5

Ramanspectraoftheas-preparedWO3aftercarbonization(a)

andafterpuri?cation;(b)RamanspectrumofcommercialWC(c).RSCAdv.,2016,6,75178–75185|75181

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observedat2508cmà1)aresimilartotheRamanspectrumofthereportedgraphene.32Therefore,thethinshellshaveagra-phene-likestructureaccordingtothemorphologyandRamanspectrumofthesample.ThegraphiticcarbonphasewasnotdisplayedintheXRDresultsinFig.3becauseofthenegligibleweightofCNSinthesample.ThegraphiticstructureofthethinshellsisclearlyshowninFig.6.ThedecompositionofacarbonsourceisaprerequisiteforthegrowthofgraphenethroughtheCVDmethod.33–35Inthepresentstudy,carbonatomsfromacarbonsourceweredecomposedtocarbonizeWO3andformCNS.WO3canbefullycarbonizedwhensu?cientcarbonatoms

decomposefromthecarbonsource.TheremainingcarbonatomsaroundthesurfaceoftheformedWCareadsorbedbytheWCbecauseofitssurfaceadsorptionandcarbonsolubility(Fig.4b).Subsequently,thecarbonatomsmigratedonthesurface(Fig.4c)ordi?usedintotheWC(Fig.4d).Asthereac-tiontemperaturedecreased,thecarbonsolubilityofWCalsodecreased.Therefore,thecarbonatomsthatdissolvedinWCwouldmigratefromtheinsidetothesurface(Fig.4e–g)oftheWC,settleandexpandalongthesurfaceoftheWC,andeven-tuallycoalescetoformalargeshell.Methanolisagoodmedi-atorofthecarbonsource,23whichmeansthatwhen

Carbon nanosheet正式稿

the

Fig.6TEM(aandb)andHRTEM(c–e)imagesofthe(WC–CNS)/Ptcatalyst;EDSresult(f)oftheselectedareain(a).

75182|RSCAdv.,2016,6,75178–75185Thisjournalis?TheRoyalSocietyofChemistry2016

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PaperRSCAdvancesadditionofmethanoltothecarbonsourceisincreased,the

proportionofthecarbonsourceavailablefordecompositionof

carbonatomsdecreases.Inthepresentstudy,thedecomposi-

tionofcarbonatomsfromthecarbonsourcecanbemediated

byaddingmethanoltoethanol.Thus,thecoverageoftheWO3

orWCbycarbonatomscanberestricted,asthecarbonsource

decomposesatthebeginning.Inaddition,theformationof

athickgraphiticcarbonlayercanbeavoided,therebyleadingto

directdeoxidizationofWO3andself-growthofCNSinWCusing

methanoltomediatethedecompositionofthecarbonsource.If

methanolisnotaddedtotheethanol,athickgraphiticcarbon

layercanbeformed,asshowninESIFig.S3.?Similarly,WO3

cannotbefullycarbonized,asshowninESIFig.S4,?ifmeth-y on 30/08/2016 03:37:21.

anolaloneisusedasthecarbonsource.Aerhydrogenwas

suppliedtothereactionchamber,WCremainedinthesample,

asshowninESIFig.S5.?However,CNSpeakscannotbe

observedintheRamanspectrum,asshownininFig.5b.These

resultsdemonstratedthatCNScouldberemovedfromthe

compositeunderhydrogenatmosphereatthecarbonization

temperature.

Fig.6showstheTEMandHRTEMimagesof(WC–CNS)/Pt

compositesthatwerepreparedinhomogeneousEGsystems.

SomeisolatedWCparticleswithdiametersrangingfrom100

nmto200nmwereobserved,andotherWCparticles

conglomeratedandformedlargeparticles(darkareainFig.6a).

Inaddition,alargequantityofnanoshellscanbeobserved.The

imagewasmagnied(Fig.6b)toprovideaclearviewofthe

nanoshellswithawidthofapproximately100nm,andthe

resultisconsistentwiththeimagesdisplayedinFig.2.

Furthermore,alargenumberofnanoparticles(smalldots)

loadedonthenanoshellsandisolatedWCparticleswith

diametersofapproximately100nmareshown.Thesmalldots

ontheWCparticlescannotbeobservedeasilybecauseofthe

darknessoftheparticles.Fig.6canddshowthatthesmalldots

loadedonthenanoshellsarehomogeneousanddense,andthe

diameterofthedotsisapproximately3nm.Todescribethe

detailsoftheisolatedWCparticles,theWCparticlesinFig.6b

weremagnied,andtheresultsareshowninFig.6e.Nanoshells

thatcoverthesurfaceoftheWCparticleswereobserved,and

theirlatticespacingofapproximately0.34nmindicatedthe

crystallinestructureofthesamplewithshellmorphology.These

resultsindicatedthatthenanoshellsareCNSwithmultiple

layers.ThenumberoflayersoftheCNSisintherangeof3to8.

Homogeneousdistributionofthesmalldotswithadiameter

rangeof3to5nmloadedonthesurfaceoftheCNSandtheWC

particleswasalsoclearlyobserved.TheEDSresult(Fig.6f)and

XRDdata(Fig.7)indicatedthatthesmalldotsarePtnano-

particles,andthePtloadingisapproximately10wt%(the

selectedareainFig.6a).Moreover,thediameterofthePt

nanoparticlesisincloseagreementwiththatestimatedfrom

theScherrerformula36basedontheXRDdatashowninFig.7.

ThepresenceofWCandPtwereobviouslydisplayedthrough

XRD.However,thegraphiticcarbonstructurewasnotshownby

XRD(Fig.7)becauseofthenegligibleweightoftheCNSinthe

composite.

Themethanoloxidationreactionisalimitingreactionstep

indirectmethanolfuelcells.Inthisstudy,themethanol

Thisjournalis?TheRoyalSocietyofChemistry2016Fig.7XRDpatternofthe(WC–CNS)/Pt

Carbon nanosheet正式稿

catalyst.oxidationperformanceofthe(WC–CNS)/Ptcatalystwasinves-tigatedthroughCVin0.5H2SO4/1.0MCH3OHsolution(Fig.8).Excellentelectrochemicalactivitycanimprove

Carbon nanosheet正式稿

theFig.8CVcurvesofdi?erentcatalystsatascanningrateof100mVsà1(a);CVcurvesofthe(WC–CNS)/Ptcatalystafterdi?erentcyclesatascanningrateof100mVsà1(b).Note:Ptloadingontheworkingelectrodewascontrolledtobe0.2mgcmà2.RSCAdv.,2016,6,75178–75185|75183Published on 28 July 2016. Downloaded by Jiangxi University of Science and Technolog

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electrocatalyticpropertiesoffuelcellsandresultinahighpowerdensity.AsshowninFig.8,themainmethanoloxidationpeakofthecatalystisat0.72V,withacurrentdensityof0.079Acmà2intheanodicsweep.Inaddition,theothermethanoloxidationpeakofthesampleisat0.48V,withacurrentdensityof0.056Acmà2inthecathodicsweep.WhentheCNSinthecompositewasremoved,themethanoloxidationpeaksofthecatalystintheanodicandcathodicsweepscanalsobeobservedatthesamepotential.However,thecurrentdensityoftheWC/Ptcatalystdecreasedsharply(thecorrespondingvalueswere0.023Acmà2and0.015Acmà2,respectively).TheroleofW2Cintheelectrocatalyticactivityofthecatalysthasalsobeenexplored.Aerthe(WC–WC)samplefromWOcarbonizedat900??Cwasy on 30/08/2016 03:37:21.

increasedconductivitybetweenWCcrystallites.18,39Thus,thesynergisticandcatalyticpropertiesofthe(WC–CNS)/Ptcatalystduringmethanoloxidationcouldbearesultoftheself-regulationofthemultiplelayersofCNSintheWC.Inaddi-tion,theanti-poisoningperformanceofthecatalystwasinves-tigated.ThecatalystshowedasimilarIf/Ib(inwhichIfandIbaretheforwardandbackcurrentdensities,respectively)value(1.41)tothatoftheWC/Ptcatalyst,asshowninFig.8,intherstcycle.Thisndingsuggestedthatself-generatedCNSonWCdoesnota?ecttheanti-poisoningpropertiesofWC,40whileW2CinWCdecreasestheanti-poisoningpropertiesofWC(If/Ibvalueis1.38).Thestabilityoftheanti-poisoningpropertiesofthecomposite(WC–CNS)/Ptcatalystwasfurtherstudied.TheI/23loadedwithPtparticles((WC–W2C)/Pt),thecorrespondingcurrentdensitiesof(WC–W22C)/Pt,showninESIFig.S6,?are0.018Acmàand0.013Acmà2,respectively.TheseresultsdemonstratedthattheW2CphaseinWCwilldeterioratetheelectrocatalyticactivityofthecatalyst.ThereasonmaybethethermodynamicandkineticinstabilityofW2C.37,38Whenmethanolwasnotaddedtotheethanolduringcarbonization,athickgraphiticcarbonlayerformedontheWCsurface,therebyproducing(WC–thickcarbon).(WC–thickcarbon)/PtcatalystwasobtainedbyloadingPtparticleson(WC–thickcarbon),andthecorrespondingcurrentdensitiesofthecatalyst,showninESIFig.S6,?are0.035Acmà2and0.021Acmà2,respectively.Inaddition,theCVcurvesofPtparticlesloadedonDWCNTsweremeasured,andtheelectrochemicalactivityoftheDWCNTs/Ptwaslowerthanthatof(WC–CNS)/Pt,asdisplayedinESIFig.S6.?Furthermore,lowelectrochemicalactivityofWCandWC–CNSwasdemonstrated.Thus,athinlayerofgraphiticcarbononWCcanincreasetheelectrochemicalactivityaerPtisloadedonitssurface.

TheCVcurvesofthe(WC–CNS)/PtandWC/PtcatalystswerealsoconductedinH2SO4,andtheresultsareshowninESIFig.S7.?ThePtcatalystbasedonWC–CNSdemonstratedhigherhydrogendesorption/adsorptionpeaksand,thus,higheractivitythanthePtcatalystbasedonWC.Theelectrochemicalsurfacearea(ESA)isanimportantparameterforcharacterizingtheelectroactivityofacatalyst.TheESAisestimatedfromESA?Q/(mb),whereQisthechargeforhydrogendesorptionwithoutthecontributionfromtheelectricdoublelayersandcanbecalculatedfromitsCV,misthequantityofPt,andbisthechargerequiredtooxidizeamonolayerofH2onbrightPt.CalculationsbasedontheCVsshowthattheESAofthe(WC–CNS)/Ptcatalyst(61.6m2gà1)islargerthanthatofWC/Pt(25.3m2gà1).Therefore,thehighelectrochemicalactivityof(WC–CNS)/PtinH2SO4wasdemonstrated.

ThehighelectrochemicalactivityoftheWC–CNSmaybeattributedtotheshellmorphologyandsmallsizeofCNSinthepreparedWCphase.ThepresenceofhomogeneousCNSdistributedintheWCpreventedtheagglomerationofthecrystalseedsoftheloadedPt.Therefore,theformationofsecondaryseedgrowthwasrestricted,whichresultedinthedirectdepositionandgrowthofPtseedswhenusingCNSinWCasasupport.Moreover,theCNSinWCsignicantlyinuencedthesizeandmorphologyofthedepositedPtnanoparticlesfromthereactionofH2PtCl6andEG.Finally,theCNSmayprovide

75184|RSCAdv.,2016,6,75178–75185fIbvaluedecreasedgraduallywithincreasingnumberofcycles(Fig.8b).If/Ibdecreasedto1.02aer300cycles,whichissimilartotheresultfortheWC/Ptcatalystaer300cycles(theIf/IbofWC/PtisshowninESIFig.S8?).Theseresultsdemonstratedthattheself-generatedCNSinWCdidnotadverselya?ectthestabilityoftheanti-poisoningpropertiesofWC.Inaddition,thestabilitiesoftheanti-poisoningpropertiesofthecompositecatalystandWC/Ptwerestudiedin1MCH3OHand0.5MH2SO4solutionat0.7Vviachronoamperometric(CA)experi-ments.TheCAresultsareshowninESIFig.S9.?Thecurrentdensityofthe(WC–CNS)/PtcatalystwashigherthanthatofWC/Ptatalongerduration,therebyindicatingthatCNSonWCcanimprovetheelectrocatalyticactivityandstabilityoftheWC.

4.Conclusions

AcarbonshellCNSstructurewaspreparedthroughaninsitudeoxidizationapproach.ThisCNShasawidthofapproximately100nmandisnearlytransparent;itprecipitatedonWCparti-cleswithdiametersrangingfrom100nmto200nm.Whenmethanolwasaddedtothecarbonsource,carbonatomsdecomposedfromthecarbonsource;thus,thecarbonsourcewasmediatedbymethanol.Moreover,fullcoverageoftheWO3orWCwithcarbonatomscouldberestrainedasthecarbonsourcedecomposed.Thus,WCcanbeobtainedbythedi?usionofcarbonatomsfromthesurfacetoinsidetheWO3.Further-more,theremainingcarbonatomsaroundthesurfaceoftheWCwouldbeadsorbed.Subsequently,thecarbonatomsmigratedintotheWCasareactiontotheincreaseintemper-atureandmigratedoutoftheWCasthetemperaturedecreased.Consequently,acarbonsheetwasformed,andthecarbonatomssettledandexpandedalongthesurfaceoftheWC.AerPtparticleswereloadedontheWC–CNScomposite,excellentelectrochemicalactivityandstabilityoftheanti-poisoningpropertiesoftheelectrocatalystwereachieved.Therefore,theWC–CNScompositecouldbepotentiallyappliedinelectro-chemistryandrelatedeldsbecauseofitsdistinctmorphologyandsize.

Acknowledgements

ThisworkwassupportedbytheNationalNaturalScienceFoundationofChina(51202095and51264010),theDepartmentofScience&TechnologyofJiangxiProvince(20153BCB23011,

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20133BBE50005,20142BDH80025,andGJJ150617)andtheprogramforExcellentYoungTalents,JXUST.

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