Preparation of Fe3O4 with high specific surface area and imp

Nanoscale

PAPER

PreparationofFe3O4withhighspeci csurfaceareaandimprovedcapacitanceasasupercapacitor

LuWang,abHongmeiJi,aShashaWang,aLijuanKong,aXuefanJiangaandGangYang*ab

Here,wereportforthe rsttimeafacileultrasonicsynthesisofFe3O4nanoparticlesusingFeCl3andtheorganicsolventethanolamine(ETA).TheintermediateoftheETA¨CFe(II)complexproducesFe3O4afterhydrolysisandhydrothermaltreatment.ThemoderatereductionofETAandultrasoundplayanimportantroleinthesynthesisofsuper neFe3O4particleswithaveryhighspeci csurfacearea(165.05m2gÀ1).TheFe3O4nanoparticleswerecharacterizedbyX-raydi raction(XRD),scanningandtransmissionelectronmicroscopy(SEMandTEM),high-resolutiontransmissionelectronmicroscopy(HRTEM),andultraviolet-visibleabsorptionspectroscopy(UV-vis).Fe3O4asanelectrodematerialwasfabricatedintoasupercapacitorandcharacterizedbycyclicvoltammetry(CV),electrochemicalimpedancespectroscopy(EIS),andgalvanostaticcharge¨Cdischargemeasurements.Theas-synthesized

Received15thJanuary2013Accepted21stFebruary2013DOI:10.1039/http://doc.guandang.net/nanoscale

Citethis:Nanoscale,2013,5,3793

Fe3O4exhibitsremarkablepseudocapacitiveactivitiesincludinghighspeci ccapacitance(207.7FgÀ1at0.4AgÀ1),goodratecapability(90.4FgÀ1at10AgÀ1),andexcellentcyclingstability(retention100%after2000cycles).ThisnovelsyntheticroutetowardsFe3O4isaconvenientandpotentialwayofproducingasecondaryenergymaterialwhichisexpectedtobeapplicableinthesynthesisofothermetaloxidenanoparticles.

1Introduction

Supercapacitorsareconsideredoneofthenewestinnovationsinthe¬èeldofelectricalenergystorage.Inrecentyears,super-capacitorshaveattractedmuchattentionfortheirhigherpowerdensitycomparedtobatteriesandhigherenergydensitycomparedtocommoncapacitors.1¨C6Accordingtotheenergystoragemechanism,electrochemicalcapacitorscanbeclassi¬èedaselectricdouble-layercapacitors(EDLCs)andfaradaicpseu-docapacitors.InEDLCs,energystoragearisesfromtheaccu-mulationofelectronicandionicchargesattheinterfacebetweentheelectrodematerialsandtheelectrolytesolution.However,thelimitedspeci¬èccapacitanceofEDLCsisfarfromperfectconsideringtheever-growingneedforpeakpowerinelectricvehicles.7¨C9Incontrast,faradaicpseudocapacitorsexhibitmuchhigherspeci¬èccapacitanceandenergydensityduetotheirreversiblemultielectronredoxfaradaicreactions.9¨C13

Metaloxidesareusuallyusedaspseudocapacitorelectrodematerials.Recently,ironferriteofFe3O4hasemergedasapotentiallypromisingsupercapacitormaterialduetoitslowcost

a

JiangsuLaboratoryofAdvancedFunctionalMaterials,DepartmentofChemistry,ChangshuInstituteofTechnology,Changshu215500,China.E-mail:gyang@http://doc.guandang.net;Fax:+86-512-52251842;Tel:+86-512-52251895

SchoolofMaterialScienceandEngineering,JiangsuUniversityofScienceandTechnology,Zhenjiang212003,China Electronicsupplementary10.1039/c3nr00256j

information

(ESI)

available.

See

DOI:

b

andenvironmentallybenignnature.14¨C17Intheconventionalway,itisverydi culttoprepareFe3O4byjustusingtrivalentiron,andthedegreeofoxidationinthesyntheticprocessshouldbestrictlycontrolledifonlyferrousisusedtosynthesizeFe3O4.ManystudieshavereportedthepreparationofFe3O4bymixingFe2+andFe3+indi erentratios,butthemethodiscomplicated.18¨C20TableS1(seetheESI )summarizestypicalresultsthathavebeenobtainedforFe3O4astheelectrodematerialforsupercapacitors.However,untilnow,duetotheeasyreunionamongthemagneticFe3O4particles,resultinginlargeparticlesizeandlowspeci¬ècsurfacearea,thespeci¬èccapacitancehashardlyreachedahighvalue.21¨C28Toaddressthisissue,anultrasonic-assistedtechniqueinsteadofmechanicalstirringwasemployedtoprepareFe3O4nanoparticles.Theuseofultrasonicirradiationfortheproduc-tionofnanomaterialshasbeenaresearchtopicofgreatinterest.Thisisduetothesimplicityofthesonochemicalmethod,thecheappriceoftheequipmentandthatinmanycasestheas-preparedmaterialisobtainedinthecrystallinephase.Forexample,B.Tangetal.introducedultrasoundtreatmentintoachemicalco-precipitationandfoundthatultrasonicationcouldsuccessivelycontrolthesizeofparticles.ThesynthesizedcubicFe3O4particleshadhighcrystallinityandhomogeneoussizedistribution,andexhibitedsuperparamagneticbehavior.29R.AbuandA.GedankenfoundthatitwaspossibletostabilizenanometersizedFe3O4inanaqueousphasedirectly,becauseultrasoniccavitationcouldpreventFe3O4agglomerationandpermittheisolationofnanocolloids.30

ThisjournalisªTheRoyalSocietyofChemistry2013Nanoscale,2013,5,3793¨C3799|3793

Nanoscale

Here,we¬èrstprovideafacilesynthesisofsuper¬èneFe3O4particlesusingtheinorganicsaltFeCl3andtheorganicsolventethanolamine(ETA)withmoderatereduction.Theas-synthe-sizedFe3O4nanoparticleswithdiametersof5¨C10nmandaveryhighspeci¬ècsurfaceareaof165.05m2gÀ1exhibitahighspeci¬èccapacitanceof207.7FgÀ1at0.4AgÀ1whichisbyfarthehighestreportedintheliteratureforFe3O4astheelectrodematerialofsupercapacitors(seeTableS1 ).ThisnovelsyntheticroutetowardsFe3O4isaconvenientandpotentialwayforproducingasecondaryenergymaterialthatisexpectedtobeapplicableinthesynthesisofothermetaloxidenanoparticles.

2

Experimental

2.1

Materialsyntheses

SynthesisofH-Fe3O4nanoparticles.Inatypicalprocedure,6mmolFeCl3wasaddedto60mLETAinbatches(0.1ghÀ1)undermechanicalstirring.A«àerFeCl3wastotallydissolvedinETA,100mLofdistilledwaterwasaddedtotheresultingcolloidalsolution.ThemixturewastransferredandsealedinaTe¬éon-linedautoclave(¬èlleddegreeis70%duetotheorganicsolventused),andheatedat180 Cfor10hours.A«àerhydro-thermaltreatment,theclearbrownmixtureturnedintoanorangesuspension.Theresultingsuspensionwasthencentri-fugedat8000rpmfor5minandwashedrepeatedlywithH2OtoremovetheresidualETAuntilthepHofthe¬èltratewasneutral.TheFe3O4nanoparticlesweredriedat60 Cinavacuumandcollectedasadarkbrownpowder.Theas-synthesizedproductobtainedthroughthehydrothermalmethodwasnamedH-Fe3O4(whereHstandsforhydrothermal).

SynthesisofUH-Fe3O4nanoparticles.6mmolFeCl3and60mLETAwereaddedintoabeaker,an ¡­¡­ ´Ë´¦Òþ²Ø£º24677×Ö£¬È«²¿ÎĵµÄÚÈÝÇëÏÂÔغó²é¿´¡£Ï²»¶¾ÍÏÂÔØ°É ¡­¡­