石墨烯负载-英文文献

NanoRes.2011,4(8):729–736729AdvancedAsymmetricalSupercapacitorsBasedonGrapheneHybridMaterialsHailiangWang,YongyeLiang,TissaphernMirfakhrai,ZhuoChen,HernanSanchezCasalongue,andHongjieDai()DepartmentofChemistry,StanfordUniversity,Stanford,CA94305,USAReceived:16February2011/Revised:12March2011/Accepted:13March2011©TsinghuaUniversityPressandSpringer-VerlagBerlinHeidelberg2011ABSTRACTSupercapacitorsoperatinginaqueoussolutionsarelowcostenergystoragedeviceswithhighcyclingstabilityandfastcharginganddischargingcapabilities,butgenerallysufferfromlowenergydensities.Here,wegrowNi(OH)2nanoplatesandRuO2nanoparticlesonhighqualitygraphenesheetsinordertomaximizethespecificcapacitancesofthesematerials.WethenpairupaNi(OH)2/grapheneelectrodewithaRuO2/grapheneelectrodetoaffordahighperformanceasymmetricalsupercapacitorwithhighenergyandpowerdensityoperatinginaqueoussolutionsatavoltageof~1.5V.TheasymmetricalsupercapacitorexhibitssignificantlyhigherenergydensitiesthansymmetricalRuO2–RuO2supercapacitorsorasymmetricalsupercapacitorsbasedoneitherRuO2–carbonorNi(OH)2–carbonelectrodepairs.Ahighenergydensityof~48W·h/kgatapowerdensityof~0.23kW/kg,andahighpowerdensityof~21kW/kgatanenergydensityof~14W·h/kghavebeenachievedwithourNi(OH)2/grapheneandRuO2/grapheneasymmetricalsupercapacitor.Thus,pairingupmetal-oxide/grapheneandmetal-hydroxide/graphenehybridmaterialsforasymmetricalsupercapacitorsrepresentsanewapproachtohighperformanceenergystorage.KEYWORDSAsymmetricalsupercapacitor,graphene,Ni(OH)2,RuO2,hybridnanomaterials,energystorageSupercapacitorsarerecognizedasanimportanttypeofdevicefornextgenerationenergystorageduetotheirhighpowerdensitiesandexcellentcyclingstability[1–6].Theycanbeusedaspowersupplieswherefastandhighpowerdeliveryanduptakeareneeded,suchasemergencydoorsonairplanes.Theycanalsoprovidetransientpowerassistancetobatteriesandfuelcellsinelectricvehicles.Therearetwotypesofsupercapacitorswhichdifferintheenergystoragemechanisminvolved—namelyelectricaldoublelayer(EDL)capacitorsbasedonionadsorption,andpseudo-capacitorsbasedonelectrochemicalredoxreactions[1,5,6].Thelattergenerallyexhibitmuchhigherspecificcapacitancesthantheformerandhavebeenusedtobuildasymmetricalsupercapacitorswithimprovedenergyandpowerdensities[1,6–13].Nevertheless,theenergydensitiesofsupercapacitorswhichcanoperateinaqueoussolution—whichislowcostandsafe(non-inflammable)—remainlowcomparedtobatteries.Graphenehasemergedasapromisingmaterialinenergystorageandconversionapplicationsduetoitshighsurfaceareaandelectricalconductance[14–24].ChemicallyderivedgraphenehasshownsignificantlyNanoRes.2011,4(8):729–736ISSN1998-0124DOI10.1007/s12274-011-0129-6CN11-5974/O4ResearchArticleAddresscorrespondencetohdai@stanford.eduNanoRes.2011,4(8):729–736730higherspecificcapacitiesthangraphite,whichhastraditionallybeenemployedastheanodematerialforlithiumionbatteries[14,15].Graphenesheetsobtainedbyreducinggrapheneoxide(GO)arealsopromisingmaterialsfordoublelayersupercapacitors[16–18].Ontheotherhand,grapheneisanidealsubstrateforgrowingbatteryorsupercapacitorelectrodenanomaterialstoincreasecapacityandrateperformancebyfacilitatingelectrontransfer[19–22].Interactionswithgraphenecouldalsohelptocontrolthenanocrystallinemorphologyofactivematerialsandincreasestabilityduringcycling[19–23].RecentlywehavesynthesizedhexagonalcrystallinenanoplatesofNi(OH)2ongraphenesheetsanddemonstratedhighspecificcapacitancesathighrateswiththishybridmaterial[22,23].Here,wehavefabricatedasymmetricalsuper-capacitorsbydevelopingaRuO2/graphenehybridmaterialandcombiningitwithaNi(OH)2/grapheneelectrode.Theasymmetricalsupercapacitorthusobtainedshowedahighenergydensityof~48W·h/kgatapowerdensityof~0.23kW/kg,andahighpowerdensityof~21kW/kgatanenergydensityof~14W·h/kg,allwitha1.5Vcellvoltageoperatingin1mol/LKOHaqueoussolutions.Theasymmetricalsupercapacitordeliveredhigherenergyandpowerdensitiesthansomeofthebestreportedaqueous-basedsupercapacitors,includingonesbasedonRuO2(oneofthehighestenergycapacitysupercapacitormaterials).Thisisthefirsttimethatnickelhydroxideandrutheniumoxidenanomaterialshavebeenpaireduptoproducesuper-capacitorswithhighenergyandpowerdensities.TheNi(OH)2/graphenehybridwassynthesizedbyatwo-stepsolutionphaseapproach[23],affordingsingle-crystallinehexagonalNi(OH)2nanoplates(thickness<10nm)onchemicallyexfoliatedgraphenesheets(GS,Fig.1(a))thatareidealforhighcapacitysupercapacitorapplications[22].Notethatthegraphenesheetsusedinthispaperweremadebyamildchemicalexfoliation–intercalationmethodresultingingrapheneFigure1Ni(OH)2/graphenehybridmaterial:(a)SEMimageofNi(OH)2nanoplatesgrownongraphenesheets;(b)CVcurvesofNi(OH)2/graphenehybridatvariousscanratesin1mol/LKOH;(c)averagespecificcapacitanceofNi(OH)2/graphenehybridatvariousscanratesbasedonCVdata;(d)averagespecificcapacitanceofNi(OH)2/graphenehybridatvariousgalvanostaticchargeanddischargecurrentdensities.InsetshowsagalvanostaticchargeanddischargecurveofNi(OH)2/graphenehybridatacurrentdensityof2A/gNanoRes.2011,4(8):729–736731sheetswithsignificantlyhigherquality(loweroxygencontentandhigherelectricalconductivity)thancommonlyusedreducedgrapheneoxide[22,23,25].TheNi(OH)2/graphenehybridmaterialshowedhighspecificcapacitanceandratecapability[~855F/gat5mV/sand~560F/gat40mV/sasmeasuredbycyclicvoltammetry(CV),basedonthetotalmassofthehybrid]withinavoltagerangeof0–0.55Vvs.aAg/AgClreferenceelectrode(Figs.1(b)–1(d)).CombiningacounterelectrodematerialhavingsimilarlyhighperformancewiththeNi(OH)2/grapheneshouldresultinsupercapacitorswithhighelectrochemicalperformance.Here,wedevelopedaRuO2/graphenehybridelectrodetocouplewiththeNi(OH)2/graphenematerial.TheRuO2/graphenehybridwasmadeintwosteps(seetheElectronicSupple-mentaryMaterial(ESM)fordetails)insolutionphase(Fig.2(a)),affordingsmallRuO2nanoparticlesselec-tivelygrownongraphenesheets(Figs.2(b)and2(c)).TheRuO2nanoparticlesgrownongraphenewerelessthan10nmindiameter,asrevealedbythescanningelectronmicroscopy(SEM)andtransmissionelectronmicroscopy(TEM)(Figs.2(b)and2(c)).TheRuO2/graphenehybridmaterialwasfirstcharacterizedbyCVmeasurementsagainstaAg/AgClreferenceelectrodeina0.2Vto–1.0Vvoltagerangein1mol/LKOHaqueoussolutions(Fig.2(d)).TheRuO2/graphenehybridshowedaspecificcapacitanceFigure2RuO2/graphenehybridmaterial.(a)Aschematictwo-stepgrowthofRuO2nanoparticlesongraphenesheets.(b)SEMimageofRuO2nanoparticlesongraphenesheets.(c)TEMimageofRuO2nanoparticlesongraphenesheets.TheinsetshowstheelectrondiffractionpatternoftheRuO2nanoparticlesongraphene.(d)CVcurvesoftheRuO2/graphenehybridatvariousscanratesin1mol/LKOH.(e)AveragespecificcapacitanceoftheRuO2/graphenehybridatvariousscanratesbasedonCVdataNanoRes.2011,4(8):729–736732of~367F/g(basedonthetotalmassofthehybrid)atascanrateof2mV/s.Thespecificcapacitancedecreasedto~280F/gwhenthescanratewasincreasedto40mV/s(Fig.2(e),bluedatapoints),suggestinggoodratecapa-bilityoftheRuO2/graphenehybridmaterial.Sincethehybridcontained~33wt%ofgraphenesheets,thespecificcapacitancesbasedonthemassofRuO2alonewouldbe~1.5timeshigher(Fig.2(e),reddatapoints).ThespecificcapacitancevaluesofourRuO2/graphenehybridarehighlycompetitivewithotherRuO2materialsmeasuredinalkalineelectrolytes[26–28].AlthoughhighercapacitanceshavebeenmeasuredforRuO2inacidicelectrolytes[21,29–33],alkalineelectrolytesarerequiredbytheNi(OH)2/graphenehybrid,whichisthecounterelectrodeofRuO2/grapheneintheasymmetricalsupercapacitorasshownbelow.ElectrochemicalmeasurementsofanasymmetricalsupercapacitorcomposedofaNi(OH)2/grapheneelec-trode(~1mg)andaRuO2/grapheneelectrode(~1mg)werecarriedoutinatwo-electrodeconfigurationinabeakercell.ThehybridmaterialswereloadedontoNifoamsubstrateswith2wt%polytetrafluoroethylene(PTFE)mixedinasbinder.ThemassratioofthetwoelectrodeswaschosentomakethecapacitanceoftheNi(OH)2/grapheneelectrodeapproximatelytwicethatoftheRuO2/grapheneelectrode,resultinginavoltagedropof~0.5VattheNi(OH)2/grapheneelectrodeand~1VattheRuO2/grapheneelectrode,givingatotalcellvoltageof~1.5V.NotethatthespecificcapacitanceandcurrentdensityvaluesofthesupercapacitorsreportedbelowareallbasedonthetotalmassofthetwoelectrodesexcludingtheNifoamsupport.Figure3(a)showstheCVcurves(ina1.5Vwindowinatwo-electrodeconfiguration)ofanasymmetricalsupercapacitorcomposedofNi(OH)2/grapheneandRuO2/grapheneelectrodes.Atotalspecificcapacitanceof~153F/gwasobtainedatalowscanrateof2mV/s(Fig.3(b)),basedonthetotalmassofNi(OH)2/grapheneandRuO2/graphenehybrids.Thecapacitancewasstill~97F/gatahighscanrateof80mV/s(Fig.3(b)).Thehighspecificcapacitanceandratecapabilityoftheasymmetricalsupercapacitorwerealsorevealedbygalvanostaticmeasurements(Figs.3(c)and3(d)).Thespecificcapacitancewas~160F/gatacurrentdensityof0.5A/g.Atahighcurrentdensityof20A/g,ausefulcapacitanceof~97F/gwasmeasured.Interestingly,thecharge–dischargevoltageprofilesofourasymmetricalsupercapacitorweresimilartothoseofelectricaldoublelayersupercapacitors(Fig.3(c)),despitethebattery-likecharginganddischargingbehaviouroftheNi(OH)2/graphenematerial(Fig.1(b),1(d)inset)[22].Theasymmetricalsupercapacitoralsoexhibitedgoodcyclingstability(Figs.3(e)and3(f))withastablecapacitance(~92%oftheoriginalcapacitance)after~5000cyclesofcharginganddischargingatacurrentdensityof10A/g.TheCoulombicefficiencywascloseto100%duringcycling.Importantly,theasymmetricalsupercapacitorexhibitedahighenergydensityof~48W·h/kgatapowerdensityof~0.23kW/kg,andahighpowerdensityof~21kW/kgatanenergydensityof~14W·h/kg(Fig.4).Thehighperformanceofourasymmetricalsuper-capacitorcanbeattributedtotheindividualpropertiesofhybridelectrodematerialsandtheircombination.BothNi(OH)2andRuO2arepseudocapacitormate-rialswithhightheoreticalspecificcapacitance.ThegrowthofactiveNi(OH)2andRuO2nanomaterialsonhighlyconductinggraphenesheetsaffordsoptimalspecificcapacitanceofthesematerials,especiallyinaqueouselectrolytes.PairingofthehighperformanceNi(OH)2/grapheneandRuO2/graphenehybridelec-trodesalsoexpandstheoperatingvoltageoftheasymmetricalsupercapacitorto~1.5V.Incontrast,themaximumoperatingvoltagerangeofsymmetricalsupercapacitorsmadeofRuO2-basedelectrodesis~1Vin1mol/LKOHaqueouselectrolyte[26,27],sinceitislimitedbythestabilityoftheelectrodeathigherpotentials.AllthesefactorsleadtomuchhigherenergydensitiesforourasymmetricalsupercapacitorsmadeofNi(OH)2/grapheneandRuO2/graphenehybridmaterialsthanforsymmetricalcapacitorsmadeofeitherofthematerialsalone,orasymmetricalsuper-capacitorscomposedofahybridmaterialelectrodeandahighsurfaceareapurecarbonelectrode(alsowitha~1.5Voperatingvoltage)—asdemonstratedbelow.Inacontrolexperiment,wemadeanasymmetricalsupercapacitorbypairing~1mgofNi(OH)2/graphenehybridand~3mgofreducedHummers’grapheneoxide(RGO,seeESMforpreparationoftheRGOelectrode)[34–36].ThespecificcapacitanceofRGONanoRes.2011,4(8):729–736733Figure3ElectrochemicalcharacterizationoftheasymmetricalsupercapacitormadeofNi(OH)2/grapheneandRuO2/graphene:(a)CVcurvesatvariousscanratesinatwo-electrodeconfigurationin1mol/LKOH;(b)two-electrodespecificcapacitance(basedonCVdata)oftheasymmetricalsupercapacitoratvariousscanrates;(c)galvanostaticchargeanddischargecurvesatvariouscurrentdensities;(d)two-electrodespecificcapacitance(basedongalvanostaticdata)oftheasymmetricalsupercapacitoratvariousdischargecurrentdensities;(e)galvanostaticchargeanddischargecurvesoftheasymmetricalsupercapacitoratacurrentdensityof10A/g;(f)capacitanceretentionversuscyclenumberfortheasymmetricalsupercapacitoratagalvanostaticchargeanddischargecurrentdensityof10A/gNanoRes.2011,4(8):729–736734was~157F/gatascanrateof5mV/s(Figs.S-1(a)andS-1(b)intheESM),whichrepresentsagoodperformanceasanEDLcapacitormaterial[16–18].Nevertheless,itisstillmuchlowerthanthoseofthehybrids[~1/6ofthatofNi(OH)2/graphene].Theasym-metricalsupercapacitormadeofNi(OH)2/grapheneandRGOpairedelectrodes(ina1.5Vvoltagerange)showedspecificcapacitancesof~87F/g,~74F/g,and~47F/gatcurrentdensitiesof0.5A/g,1A/g,and10A/grespectively(Fig.S-2intheESM).Theenergydensitywas~31W·h/kgatapowerdensityof~0.42kW/kg,and~17W·h/kgat~7.8kW/kg(Fig.4).Theseperfor-mancesarecomparabletothoseofasymmetricalsupercapacitorsmadeofNi(OH)2andactivatedcarbonreportedintheliterature[7,11,13],butsignificantlylowerthantheasymmetricalsupercapacitormadeofNi(OH)2/grapheneandRuO2/graphenehybrids.NotethatasymmetricalsupercapacitormadeoftwoidenticalRGOelectrodesshowedevenlowerspecificcapacitances(only~33F/gat0.17A/g,Fig.S-1intheESM),withenergydensitiesof~9.1W·h/kgand~6.7W·h/kgatpowerdensitiesof~0.12kW/kgand~3.3kW/kgrespectively,muchworsethantheasym-metricalsupercapacitormadeofNi(OH)2/graphenepairedwithRuO2/graphene,orNi(OH)2/graphenepairedwithRGO(Fig.4).TheenergydensityofourNi(OH)2/grapheneandRuO2/grapheneasymmetricalsupercapacitorwasalsosignificantlyhigherthananyotherpuregraphenebasedsymmetricalsuper-capacitorsinaqueouselectrolytes[16–18].Thepairingofabattery-likeNi(OH)2/grapheneelectrodewithacapacitor-likeRuO2/grapheneelectrodewithnon-overlappingvoltagerangesaffordedanasymmetricalsupercapacitorwithhighcapacitance.Inacontrolexperiment,wemadeasymmetricalsupercapacitorusingtwoRuO2/grapheneelectrodesandfoundaspecificcapacitanceof~77F/gatacurrentdensityof0.5A/g(Fig.S-3intheESM).Thespecificcapacitance(~77F/g)was~1/4ofthecapacitanceofasingleRuO2/grapheneelectrode(~367F/g),duetothetwocapacitorelectrodesbeinginserieswithtwicetheelectrodemass[4],resultinginalowenergydensityof~11W·h/kgatapowerdensityof0.076kW/kg(Fig.4).Interestingly,weobservedtheasymmetricalsuperca-pacitormadeofNi(OH)2/grapheneandRuO2/grapheneexhibitedaspecificcapacitance(~153F/g)approximatelyFigure4Ragoneplot(powerdensityvs.energydensity)oftheasymmetricalsupercapacitormadeofNi(OH)2/grapheneandRuO2/graphenehybrids.ComparisonofsupercapacitorscomposedofNi(OH)2/grapheneandRGOpairedelectrodes(black),RuO2/grapheneandRuO2/graphenepair(blue),RGOandRGOpair(green)togetherwithtwosetsofreferencedata(dashedlines)halfthatofthecapacitanceofasingleRuO2/grapheneelectrode(~367F/g).TheNi(OH)2/grapheneelectrodewasbattery-like,beingchargedordischargedwithsharpthreshold-likevoltages(seeCVcurvesinFig.1(b)).Therefore,thevoltagedropsontheNi(OH)2/grapheneandRuO2/grapheneelectrodesidesarenotdividedlikeinasimplecapacitorinseriesmodel.ThisdiffersfromthesymmetricalRuO2/graphenedeviceinwhichthevoltagedropisevenlydividedbythetwoelectrodesatanypointoftimeduringcharge–discharge.RuO2hasbeenshowntobeapromisinghighenergydensitysupercapacitormaterial,withthecaveatofhighcost[21,26–33].ComparedtoRuO2basedsuper-capacitorsreportedpreviously[21,27–33],includingaRuO2/graphene–RuO2/graphenepair[21]andaRuO2–RuO2pair[31],ourasymmetricalNi(OH)2/grapheneandRuO2/graphenesupercapacitorshowshigherelectrochemicalperformance,especiallyintermsofhigherenergydensities(Fig.4).Importantly,thisim-provedperformanceinenergydensityisaccompaniedbytheeconomicbenefitofreplacingoneoftheRuO2electrodeswithalow-costNi(OH)2electrode,greatlyreducingtheamountofRuO2neededforenergystorage(by~2/3comparedtoRuO2–RuO2devices[31]),thusachievinghigherenergydensitiesatlowerNanoRes.2011,4(8):729–736735cost.ThisisthefirsttimethatNi(OH)2hasbeenusedtopairupwithRuO2ingraphene-hybridbasedsupercapacitors.Inconclusion,wehavefabricatedasymmetricalsupercapacitorsbycouplingnovelNi(OH)2/grapheneandRuO2/graphenehybridmaterials.Byvirtueofthepairingofbattery-likeNi(OH)2/graphenewithcapacitor-likeRuO2/grapheneelectrodes,theasymmetricalsupercapacitorshowedhighspecificcapacitancesandhighenergyandpowerdensitieswitha~1.5VoperatingvoltageinlowcostandhighlysafeKOHaqueouselectrolytes.Thisisthefirsttimethatnickelhydroxideandrutheniumoxidenanomaterialshavebeenpaireduptoproducesupercapacitorswithhighenergyandpowerdensities.Theperformanceofoursupercapacitorreportedhereexceedsthoseofsomeofthebestreportedsupercapacitorsoperatinginaqueouselectrolytes.AcknowledgementsThisworkwassupportedpartiallybyONRandaStanfordGraduateFellowship.ElectronicSupplementaryMaterial:Supplementarymaterial(detailsofmaterialsynthesisandelectro-chemicalmeasurements)isavailableintheonlineversionofthisarticleathttp://dx.doi.org/10.1007/s12274-011-0129-6.References[1]Burke,A.Ultracapacitors:How,whyandwhereisthetechnology?J.PowerSources2000,91,37–50.[2]Kötz,R.;Carlen,M.Principlesandapplicationsofelectro-chemicalcapacitors.Electrochim.Acta2000,45,2483–2498.[3]Winter,M.;Brodd,R.Whatarebatteries,fuelcells,andsupercapacitors?J.Chem.Rev.2004,104,4245–4269.[4]Inagaki,M.;Konno,H.;Tanaike,O.Carbonmaterialsforelectrochemicalcapacitors.J.PowerSources2010,195,7880–7903.[5]Arico,A.S.;Bruce,P.;Scrosati,B.;Tarascon,J.T.;vanSchalkwijk,W.V.Nanostructuredmaterialsforadvancedenergyconversionandstoragedevices.Nat.Mater.2005,4,366–377.[6]Simon,P.;Gogotsi,Y.Materialsforelectrochemicalcapacitors.Nat.Mater.2008,7,845–854.[7]Wang,Y.;Yu,L.;Xia,Y.ElectrochemicalcapacitanceperformanceofhybridsupercapacitorsbasedonNi(OH)2/carbonnanotubecompositesandactivatedcarbon.J.Electrochem.Soc.2006,153,A743–A748.[8]Qu,Q.;Zhang,P.;Wang,B.;Chen,Y.;Tian,S.;Wu,Y.;Holze,R.ElectrochemicalperformanceofMnO2nanorodsinneutralaqueouselectrolytesasacathodeforasymmetricsupercapacitors.J.Phys.Chem.C2009,113,14020–14027.[9]Wu,Z.;Ren,W.;Wang,D.;Li,F.;Liu,B.;Cheng,H.High-energyMnO2nanowire/grapheneandgrapheneasymmetricelectrochemicalcapacitors.ACSNano2010,4,5835–5842.[10]Li,J.;Gao,F.Analysisofelectrodesmatchingforasymmetricelectrochemicalcapacitor.J.PowerSources2009,194,1184–1193.[11]Lang,J.;Kong,L.;Liu,M.;Luo,Y.;Kang,L.Asymmetricsupercapacitorsbasedonstabilizedα-Ni(OH)2andactivatedcarbon.J.SolidStateElectrochem.2010,14,1533–1539.[12]Wang,H.;Gao,Q.;Hu,J.AsymmetriccapacitorbasedonsuperiorporousNi–Zn–Cooxide/hydroxideandcarbonelectrodes.J.PowerSources2010,195,3017–3024.[13]Kong,L.;Liu,M.;Lang,J.;Luo,Y.;Kang,L.Asymmetricsupercapacitorbasedonloose-packedcobalthydroxidenanoflakematerialsandactivatedcarbon.J.Electrochem.Soc.2009,156,A1000–A1004.[14]Yoo,E.;Kim,J.;Hosono,E.;Zhou,H.;Kudo,T.;Honma,I.LargereversibleListorageofgraphenenanosheetfamiliesforuseinrechargeablelithiumionbatteries.NanoLett.2008,8,2277–2282.[15]Bhardwaj,T.;Antic,A.;Pavan,B.;Barone,V.;Fahlman,B.D.Enhancedelectrochemicallithiumstoragebygraphenenanoribbons.J.Am.Chem.Soc.2010,132,12556–12558.[16]Stoller,M.D.;Park,S.;Zhu,Y.;An,J.;Ruoff,R.S.Graphene-basedultracapacitors.NanoLett.2008,8,3498–3502.[17]Wang,Y.;Shi,Z.;Huang,Y.;Ma,Y.;Wang,C.;Chen,M.;Chen,Y.Supercapacitordevicesbasedongraphenematerials.J.Phys.Chem.C2009,113,13103–13107.[18]An,X.;Simmons,T.;Shah,R.;Wolfe,C.;Lewis,K.M.;Washington,M.;Nayak,S.K.;Talapatra,S.;Kar,S.Stableaqueousdispersionsofnoncovalentlyfunctionalizedgraphenefromgraphiteandtheirmultifunctionalhigh-performanceapplications.NanoLett.2010,10,4295–4301.[19]Wang,H.;Cui,L.;Yang,Y.;Casalongue,H.S.;Robinson,J.T.;Liang,Y.;Cui,Y.;Dai,H.Mn3O4–graphenehybridasahigh-capacityanodematerialforlithiumionbatteries.J.Am.Chem.Soc.2010,132,13978–13980.[20]Yang,S.;Cui,G.;Pang,S.;Cao,Q.;Kolb,U.;Feng,X.;Maier,J.;Mullen,K.FabricationofcobaltandcobaltNanoRes.2011,4(8):729–736736oxide/graphenecomposites:Towardshigh-performanceanodematerialsforlithiumionbatteries.ChemSusChem2010,3,236–239.[21]Wu,Z.;Wang,D.;Ren,W.;Zhao,J.;Zhou,G.;Li,F.;Cheng,H.AnchoringhydrousRuO2ongraphenesheetsforhigh-performanceelectrochemicalcapacitors.Adv.Funct.Mater.2010,20,3595–3602.[22]Wang,H.;Casalongue,H.S.;Liang,Y.;Dai,H.Ni(OH)2nanoplatesgrownongrapheneasadvancedelectrochemicalpseudocapacitormaterials.J.Am.Chem.Soc.2010,132,7472–7477.[23]Wang,H.;Robinson,J.T.;Diankov,G.;Dai,H.Nanocrystalgrowthongraphenewithvariousdegreesofoxidation.J.Am.Chem.Soc.2010,132,3270–3271.[24]Liang,Y.;Wang,H.;Casalongue,H.S.;Chen,Z.;Dai,H.TiO2nanocrystalsgrownongrapheneasadvancedphotocatalytichybridmaterials.NanoRes.2010,3,701–705.[25]Li,X.;Zhang,G.;Bai,X.;Sun,X.;Wang,X.;Wang,E.;Dai,H.HighlyconductinggraphenesheetsandLangmuir–Blodgettfilms.Nat.Nanotechnol.2008,3,538–542.[26]Lin,Y.;Lee,K.;Chen,K.;Huang,Y.SuperiorcapacitivecharacteristicsofRuO2nanorodsgrownoncarbonnanotubes.Appl.Surf.Sci.2009,256,1042–1045.[27]Wang,Y.;Wang,Z.;Xia,Y.AnasymmetricsupercapacitorusingRuO2/TiO2nanotubecompositeandactivatedcarbonelectrodes.Electrochim.Acta2005,50,5641–5646.[28]Liu,Y.;Zhao,W.;Zhang,X.SofttemplatesynthesisofmesoporousCo3O4/RuO2·xH2Ocompositesforelectrochemicalcapacitors.Electrochim.Acta2008,53,3296–3304.[29]Bi,R.;Wu