MaterialsLetters112(2013)158–161ContentslistsavailableatScienceDirectMaterialsLettersjournalhomepage:www.elsevier.com/locate/matletNanoCeO2/activatedcarbonbasedcompositeelectrodesforhighperformancesupercapacitorL.S.Aravindaa,K.UdayaBhatb,BadekaiRamachandraBhata,nabCatalysisandMaterialsLaboratory,DepartmentofChemistry,NationalInstituteofTechnologyKarnataka,Surathkal,D.K.,Karnataka575025,IndiaDepartmentofMaterialsandMetallurgicalEngineering,NationalInstituteofTechnologyKarnataka,Surathkal,D.K.575025,Karnataka,IndiaarticleinfoArticlehistory:Received24July2013Accepted4September2013Availableonline13September2013Keywords:NanocompositeEnergystorageandconversionCarbonmaterialsabstractCeriumoxide(CeO2)/Activatedcarbon(AC)basedcompositewerepreparedbysimplemechanicalmixingmethodwithhighdegreeofscalability.ThesampleswerecharacterizedusingX-raydiffraction(XRD),Fieldemissionscanningelectronmicroscope(FESEM)andTransmissionelectronmicroscope(TEM).Thecompositemixturewith10wt%(weight%)CeO2exhibitsaspecificcapacitanceof162FgÀ1intwoelectrodeconfiguration.Thetestcellretains86%specificcapacitanceevenathighcurrentdensitywithexcellentcyclestability.Thecompositeelectrodeexhibitsapowerdensityof3500WkgÀ1atahighcurrentdensity,suggestingagoodelectrodematerialforsupercapacitor.&2013ElsevierB.V.Allrightsreserved.1.IntroductionElectrochemicalsupercapacitorsarecleanenergystoragedeviceusedinvariousapplicationslikeconsumerelectronics,hybridelectricvehiclesandotherapplications[1].Carbonbasedelectrodematerialsareusedaselectrodematerialforelectroche-micaldoublelayer(EDLCs)supercapacitorswhereasconductingpolymerormetaloxidebasedmaterialsareusedaspsuedocapa-citor.Forachievingbetterperformance,thecompositeofcarbo-naceousmaterialsandmetaloxideorconductingpolymerswerebeingused.Inordertosatisfygrowingdemandsforbetterperformancewithhigherenergy/powerdensitiesandlongercyclelife,searchfornewelectrodematerialsareverymuchessential.LowcostenvironmentalfriendlinessandbetterelectrochemicalredoxcharacteristicsmakeCeO2agoodcandidateforelectrodematerial[2,3].Thoughthenanocarbonmateriallikegraphene,carbonnanotubesanditscompositeexhibithighspecificcapaci-tance,butthesematerialsarecostlyanddifficulttoprepare.Activatedcarbonbasedsupercapacitorismoreusefulduetoitslowcost,abundantavailability,andhighsurfacearea[4].Inthiswork,weinvestigatedtheintroductionofCeriumoxidenanopar-ticlesintoactivatedcarbonstoenhanceEDLCcapacitanceofactivatedcarbon.TheintroductionofCeriumoxidenanoparticleswascarriedoutbythesimplemechanicalmixingmethod.Theadvantagesofthismethodare(i)Simplesyntheticrouteatroomtemperatureinshortdurationoftime,(ii)controlovermassofadditionofCeO2onActivatedcarbonand(iii)lowcostmaterialandhencethemethodiseconomical.2.ExperimentalCeO2nanoparticleswerepreparedbydropwiseadditionof5MKOHsolutionintoabeakercontaining1MCe(NO3)3aqueoussolutionundervigorousstirring.Thestirringwascontinuedfor1h,ayellowishwhiteprecipitatewasformed.Theprecipitatewasfilteredandwashedwithdeionisedwateranddriedat1501C.ThecompositemixtureofCeO2/ACcompositewaspreparedbysimplemixing0,5,10,and15wt%ofCeO2withactivatedcarbonusingmixermill.Thecompositewith0,5,10,and15wt%ofCeO2withactivatedcarbonwerenamedasAC,A-1,A-2andA-3respectively.X-raydiffraction(XRD)studieswereperformedbyJEOLJDX8PdiffractometerusingCuKαradiation.Thesurfacemorphologyofsampleswascharacterizedusingafieldemissionscanningelectronmicroscope(FESEM;JSM-7600F)andtransmissionelectronmicro-scope(JEOLJEM2100).Theelectrodeperformancewereevaluatedbygalvanostaticcharge–dischargestudiesatacurrentdensityrangingfrom2mAcmÀ2to18mAcmÀ2,cyclicvoltammetric(CV)studiesweredoneatascanrateof10mVsÀ1–100mVsÀ1andelectro-chemicalimpedancestudies(EIS)weremeasuredatanACfrequencyrange10mHz–100kHzusingAutolabPGSTAT-30electrochemicalworkstation.3.ResultsanddiscussionsCorrespondingauthor:Tel.:þ918242474000x3204;fax:þ918242474033.E-mailaddresses:chandpoorna@yahoo.com,brchandra@gmail.com(B.RamachandraBhat).0167-577X/$-seefrontmatter&2013ElsevierB.V.Allrightsreserved.http://dx.doi.org/10.1016/j.matlet.2013.09.009nTheX-raydiffractogrampatternofsynthesizedCeO2andA-2compositearerepresentedinFig.1a.Thediffractionpeaksat28.31,L.S.Aravindaetal./MaterialsLetters112(2013)158–161159Fig.1.(a)X-raydiffractogramofCeO2nanoparticleandA-2composite,(b)TEMimageofCeO2nanoparticleand(c)FESEMimageofand10wt%CeO2/ACcomposite.Fig.2.(a)Charge–dischargecurvesofAC,A-1,A-2,andA-3atacurrentdensityof2mAcmÀ2,(b)variationsofspecificcapacitancewithCeO2loading,(c)variationofspecificcapacitanceatdifferentcurrentdensity,(e)specificcapacitanceretentionwithcyclenumberand(g)RagoneplotforA-2electrodeatdifferentcurrentdensitiesfrom2mAcmÀ2to18mAcmÀ2.160L.S.Aravindaetal./MaterialsLetters112(2013)158–161Fig.3.(a)CVcurvesofA-2electrodeatascanrateof10mVsÀ1–100mVsÀ1and(b)NyquistplotofAC,A-1,A-2,A-3andinsetrepresentstheenlargedversionatlowfrequencyregion.32.91,47.31,56.01,59.61,69.01,76.71,and88.11matcheswiththecubicstructureofCeO2(JCPDS01-075-0076).ThisconfirmsthecrystallinenatureofCeO2.Furtheradditionalpeakat23.71isobservedinA-2compositealongwiththeotherCeO2peakswhichisduetothe(002)planeofAC,whichconfirmstheformationofcomposite.Fig.1brepresentstheTEMimagesofCeO2whichclearlyindicatestheformationofnanoparticle.Fig.1cindicatesthedistributionofCeO2nanoparticlesovertheAC.Electrochemicalstudies:Thecompositemixtureisdispersedinabeakercontainingethanolfor15–20minusingsonicator.Thenthesolutionwasuniformlybrushcoatedoveracarbonpaper.Thenthecarbonpaperwasvacuumdriedovernightat601C.Thecoatedcarbonpaperwasusedasaworkingelectrode.Thesupercapacitorsetupwasfabricatedbyassemblingtwo1cm2coatedcarbonmaterialbetweentwostainlesssteelplatesseparatedbyathinpaperseparatorin1MH2SO4.Thesystemwaslockedwithstainlesssteelclamps.Fig.2arepresentstheircharge–dischargecurvesofallthesamplesinthevoltagerangeof0toþ1Vatcurrentdensityof2mAcmÀ2.Thespecificcapacitance[5]energydensity(E)andpowerdensity(P)werecalculatedbythefollowingequations:Cs¼2It=mΔVE¼1000CsΔV2=4Â2Â3600P¼E=Tdð1Þð2ÞTheRagoneplotisasshownintheFig.2e.The10wt%CeO2/ACcompositebasedsymmetricsupercapacitorcouldstoreanenergydensityof5.62WhkgÀ1withpowerdensityof289WkgÀ1atacurrentdensityof2mAcmÀ2.Thecompositealsoexhibitanenergydensityof4.86WhkgÀ1withpowerdensityof3500WkgÀ1evenathighcurrentdensityof18mAcmÀ2,indicatesthehighratecapabilityoftheelectrodematerial.Fig.3arepresentsthecyclicvoltammogramsofA-2,recordedatascanrateof10mVsÀ1–100mVsÀ1.Aslightlydistortedrectangular-likeshapewithpeakswasobserved.ThesepeaksareattributedtothepseudocapacitancebehaviourofCeO2.ThelackofsymmetryintheCVcurvesmaybeduetothecombinationofbothEDLCandpseudocapacitivebehaviour.Thecapacitivebehaviourwillberetainedevenathighscanrate.EISmeasurementwascarriedoutanditscorrespondingNyquistplotisasshowninFig.3b.Alltheelectrodematerialshowsastraightlineinthelow-frequencyregionandsmallarcinthehighfrequencyregionwhichisatypicalbehaviourofsupercapacitor[9,10].FromtheNyquistplottheESRvalueswasfoundtobe0.44Ω,0.98Ω,0.55Ω,0.59ΩforAC,A-1,A-2andA-3respectively.TheRctvalueswerefoundtobe1.42Ω,0.74Ω,0.13Ω,0.59ΩforAC,A-1,A-2,A-3respectively.TheRctvalueofA-2hasgreatlyimprovedaftertheincorporationofCeO2nanoparticle,whichimprovesthechargetransferperformanceoftheelectrode.4.Conclusionsð3ÞAsimplemethodwithhighdegreeofscalabilitywasusedtopreparecomposite.Thecompositeelectrodewith10wt%CeO2exhibitsaspecificcapacitanceof162FgÀ1intwoelectrodesystem.Theelectrodeexhibitpowerdensityof3500WkgÀ1evenathighcurrentdensityof18mAcmÀ2withexcellentcyclestabilityshowsapotentialelectrodematerialforhigh-performancesupercapacitors.References[1]LuW,HartmanR.Nanocompositeelectrodesforhigh-performancesuper-capacitors.JournalofPhysicalChemistryLetters2011;43:655–60.[2]WangY,GuoCX,LiuJ,ChenT,YangH,LiCM.CeO2nanoparticles/graphenenanocomposite-basedhighperformancesupercapacitor.DaltonTransactions2011;40:6388–91.[3]MinHY,TaoST,SenNJ,MingJH.Super-capacitiveperformancesofnickelfoamsupportedCeO2nanoparticles.JournalofShanghaiJiaotongUniversity2012;17:513–6.[4]TabernaPL,SimonP,FauvarqueJF.Electrochemicalcharacteristicsandimpedancespectroscopystudiesofcarbon-carbonsupercapacitors.JournaloftheElectrochemicalSociety2003;150:A292–300.[5]BiswalM,BanerjeeA,DeoM,OgaleS.Fromdeadleavestohighenergydensitysupercapacitors.EnergyandEnvironmentalScience2013;6:1249–59.whereCsisthespecificcapacitanceofthesingleelectrode,Iisthecurrent,ΔVisthecellvoltageaftercorrectingforiRdropmisthemassoftheelectrodeandTdisthedischargingtime.Theconstants1000and3600aretheconversionfactors.ThevariationofspecificcapacitancewithCeO2loadingsareshownintheFig.2b.ThecompositeA-2showshighestcapacitancemaybeduetotheeffectofbothACaswellasCeO2.ItisobservedthatthespecificcapacitancedecreaseswithincreaseinCeO2loading.ThismaybeduetothedrasticdecreaseinsurfaceofactivatedcarbonbyCeO2[6].ThevariationofspecificcapacitanceversuscurrentdensitiesisgiveninFig.2c.Only13.6%decreaseinspecificcapacitanceevenat18mAcmÀ2indicatesthegoodcapacitiveretainingtendencyoftheelectrodematerialevenathighcurrentdensity.Thecyclingstudieswerecarriedoutfor1000cyclesat20mAcmÀ2.Thespecificcapacitanceretentionisalmostgreaterthan99%evenupto1000cycleswhichindicatesexcellentcyclestabilityofthematerial.ThespecificcapacitanceretentionwithcyclenumberisrepresentedinFig.2d.TheenergydensityandthepowerdensityofthetestcellwerecalculatedasgiveninEqs.(2)and(3)[7,8].L.S.Aravindaetal./MaterialsLetters112(2013)158–161161[6]ZhangJD,JiangB,ChenZhuJ,JiangL,FangH.Preparationandelectrochem-istryofhydrousrutheniumoxide/activecarbonelectrodematerialsforsuper-capacitor.JournaloftheElectrochemicalSociety2011;48:A1362–7.[7]BoZ,WenZ,KimH,LuG,YuK,ChenJ.One-stepfabricationandcapacitivebehaviourofelectrochemicaldoublelayercapacitorelectrodesusingvertically-orientedgraphenedirectlygrownonmetal.Carbon2012;50:4379–87.[8]Jaidev,JafriRI,MishraAK,RamaprabhuS.Polyaniline–MnO2nanotubehybridnanocompositeassupercapacitorelectrodematerialinacidicelectrolyte.JournalofMaterialsChemistry2011;21:17601–5.[9]KotzR,CarlenM.Principlesandapplicationsofelectrochemicalcapacitors.ElectrochimicaActa2000;45:2483–98.[10]LiX,RongJP,WeiBQ.Electrochemicalbehaviourofsingle-walledcarbonnanotubesupercapacitorsundercompressivestress.ACSNano2010;4:6039–49.