2013-RSC-A-MnO2@CoAl-LDH@C-超级电容器-944

Citethis:DOI:10.1039/c2ra22566bReceived18thOctober2012,Accepted16thNovember2012FlexiblehierarchicalnanocompositesbasedonMnO2nanowires/CoAlhydrotalcite/carbonfibersforhigh-performancesupercapacitors3DOI:10.1039/c2ra22566b*DavidG.EvansandXueDuanAhierarchicalnanocompositebasedonMnO2nanowire/CoAllayereddoublehydroxide/carbonfibersisfabricatedbyafaciletwo-stepmethodasahigh-performancesupercapacitor.TheCoAl-LDHnanocrystalsgrownonflexiblecarbonfiberswerepreparedviaaninsituhydrothermalmethod,followedbyloadingofMnO2nanowiresthroughadirectredoxreactionbetweentheCo2+speciesandMnO42.ThehierarchicalMnO2/LDH/CFselec-trodeasasupercapacitordisplaysahighspecificcapacitance(944Fg21at1Ag21)andratecapability,goodstabilityandexcellentlong-termcyclinglife.Tomeettheurgentneedforsustainableandrenewablepowersources,inmodernelectronicindustriesmanyeffortshavebeenmadeindevelopingflexible,lightweightandenviron-mentallyfriendlyenergystoragedevices.1,2Electrochemicalcapacitors,alsoknownassupercapacitors,3arethemostpromisingcandidatesforvariousportablesystemsandautomotiveapplicationsowingtotheirhighpowerdensity,excellentpulsecharge–dischargecharacteristicsandlongcyclelife.4–6Pseudocapacitivetransition-metaloxides,MnO2forinstance,havebeenextensivelyusedinsupercapacitorsduetotheirhighcapacitance,lowcostandenvironment-friendliness.7,8GiventhatthepoorconductivityofMnO2(1025–1026Scm21)limitsthecharge–dischargerateforhigh-powerapplications,9,10furthereffortshavebeendirectedatincorporatingMnO2nanostructureswithcarbon-basedmate-rialsorconductivepolymers.11–14AnotherproblemofMnO2materialsarisesfromthedensepackingandinaccessiblesurfaceareaasahighloadingisapplied,whichleadstoaremarkableincreaseincontactresistanceandtheresultingdecreaseinspecificcapacitance.Therefore,takingintoaccounttheefficientutilizationofthepseudocapacitanceofMnO2,itishighlyessentialtoachieveahierarchicalmorphologyandreliableelectricconnectionforthepurposeofobtaininghigh-performanceMnO2-basedsupercapacitors.Recenteffortshavebeendevotedtoexploringcompositepseudocapacitivematerials,suchasbinarymetaloxides/hydroxides15,16andmixedmetaloxides,17,18bycombiningtheuniquepropertiesofindividualconstituents.Itwasreportedthatthesynergisticeffectbetweendifferentcompositionscanbeachievedthroughsuitablemicro-/nanostructuredesign.19,20Therefore,moreadvancedandcomplexhetero-structureshavebeenfabricatedtoimprovethepseudocapa-citiveperformance,suchascore–shellstructures,21,22tube-structuredarrays,23–25coaxialnanowires26andconductivecarbon/polymersupportedmetaloxides/hydroxidescompo-sites.27–32Itisbelievedthatanidealelectrodematerialconsistsofathree-dimensional(3D)interpenetratingnetworkofelectronandionpathwaysforefficientmass/electrontransport.33–35Akeychallengeinthisdirectionistodevelopadesirableelectrodearchitecturethatfavorssufficientexpo-sureoftheelectroactivespeciesfortheFaradaicredoxreaction,andsimultaneouslyenhancethekineticsofion/electrontransportthroughouttheelectrode.Basedontheaboveconsideration,onepromisingrouteistorationallydesignandconstructthehybridizationofpseudocapacitiveoxides/hydroxideswithsophisticatednanoarchitectures,whichprovidesahighly-accessiblesurfacearea,fastiondiffusionandexcellentelectronicconductivity.Herein,wedemonstratethedesignandfabricationofanovelnanocomposite(MnO2/LDH/CFs)byloadingMnO2nanowiresontoCoAllayereddoublehydroxide(LDH)nanowallsgrownonflexiblecarbonfibers(CFs)forhigh-performancesupercapacitors.Thesingle-crystallineLDHwithahighlyaccessiblesurfaceareaservesuniquelyasareductantandtheframeworkforanchoringtheMnO2nanowiressimultaneously.BothLDHandMnO2areemployedastheactivespecies,whichcontributetothetotalspecificcapacitance;whiletheconductiveCFswithappropriatechannelsguaranteeeffectiveelectron/iontransportthroughouttheelectrode.Byvirtueofthesynergeticcontributionfromindividualconstituentsandthesophisticatedconfiguration,theresultingMnO2/LDH/CFscompositeexhibitsahighlyboostedspecificStateKeyLaboratoryofChemicalResourceEngineering,BeijingUniversityofChemicalTechnology,Beijing100029,P.R.China.E-mail:[e-mail];Fax:[phone];Tel:[phone]ElectronicSupplementaryInformation(ESI)available:Experimentalprocedures,gasadsorption/desorptionanalysis,XRDpatternsandadditionalelectrochemicaldataareincluded.SeeDOI:10.1039/c2ra22566bRSCAdvancesCOMMUNICATIONThisjournalisTheRoyalSocietyofChemistry2012RSCAdv.Downloadedon08December2012Publishedon19November2012on|doi:10.1039/C2RA22566BViewArticleOnlineViewJournalcapacitance,superiortoitssingle-componentsamples(LDH/CFsandMnO2/CFs).Inaddition,thisintegratedelectrodemanifestsaremarkableratecapabilityandexcellentlong-termcyclingstability.Therefore,thecontroloverthemulti-compositionandbottom-uparchitecturedemonstratedinthisworkoffersapromisingstrategyforthefabricationofsupercapacitormaterialsusedinelectro-chemicalenergystorage.OurstrategyisschematicallyshowninScheme1.ThepreparationprocessoftheMnO2/LDH/CFscompositemainlyinv