Manganesedioxideasanewcathodecatalystinmicrobialfu

JournalofPowerSources195(2010)2586–2591ContentslistsavailableatScienceDirectJournalofPowerSourcesjournalhomepage:∗aDepartmentofCivilandEnvironmentalEngineering,UniversityofConnecticut,Storrs,CT06269,UnitedStatesbInstituteofMaterialsScience,UniversityofConnecticut,Storrs,CT06269,UnitedStatescDepartmentofChemistry,UniversityofConnecticut,Storrs,CT06269,UnitedStatesdDepartmentofChemicalandBiomolecularEngineering,UniversityofConnecticut,Storrs,CT06269,UnitedStatesarticleinfoArticlehistory:Received23September2009Receivedinrevisedform28October2009Accepted29October2009Availableonline14November2009Keywords:MicrobialfuelcellsManganesedioxidesOctahedralmolecularsievesOxygenreductionreactionabstractThisstudyfocusedonmanganeseoxideswithacryptomelane-typeoctahedralmolecularsieve(OMS-2)structuretoreplaceplatinumasacathodecatalystinmicrobialfuelcells(MFCs).Undoped(ud-OSM-2)andthreecatalystsdopedwithcobalt(Co-OMS-2),copper(Cu-OMS-2),andcerium(Ce-OMS-2)toenhancetheircatalyticperformanceswereinvestigated.ThenovelOMS-2cathodeswereexaminedingranularactivatedcarbonMFC(GACMFC)withsodiumacetateastheanodereagentandoxygeninairasthecathodereagent.Theresultsshowedthatafter400hofoperation,theCo-OMS-2andCu-OMS-2exhibitedgoodcatalyticperformanceinanoxygenreductionreaction(ORR).ThevoltageoftheCo-OMS-2GACMFCwas217mV,andthepowerdensitywas180mWm−2.ThevoltageoftheCu-OMS-2GACMFCwas214mVandthepowerdensitywas165mWm−2.Theinternalresistance(Rin)oftheOMS-2GACMFCs(18±1)wassimilartothatoftheplatinumGACMFCs(17).Furthermore,thedegradationratesoforganicsubstratesintheOMS-2GACMFCsweretwicethoseintheplatinumGACMFCs,whichenhancetheirwastewatertreatmentefficiencies.ThisstudyindicatedthatusingOMS-2manganeseoxidestoreplaceplatinumasacathodiccatalystenhancespowergeneration,increasescontaminantremoval,andsubstantiallyreducesthecostofMFCs.PublishedbyElsevierB.V.1.IntroductionMicrobialfuelcell(MFC)technologyisanemergingbiotech-nologythatutilizesbacteriatogenerateelectricityfromthedegradationoforganicsubstances[1].TraditionalMFCsconsistofananaerobicanodeandanaerobiccathode.Bacteriadegradeorganicsubstances(e.g.,acetate,glucose)andgenerateelectronsintheanodechamber.Theelectronsaretransferredtotheanodesurfaces,whichthenflowthroughanexternalcircuittoreactwithanelectronacceptor(e.g.,oxygen,ferricyanide)inthecathodechamber,throughwhichelectricityisproduced.MFCscaneffi-cientlyconvertorganiccontaminantstocleanenergyatnormaltemperaturesandpressures,whichholdsgreatpotentialfortheirapplicationinwastewatertreatmentplantstosimultaneouslytreatwastewaterandproduceenergy.AlargeefforthasbeeninvestedtoenhanceenergyproductioninMFCs.Mostattentionwasonsubstratedegradation,electrongeneration,andtransferinanodechambers[2].Severalimportantfactorsincludingsubstrateconcentration,pH,conductivity,micro-bialactivity,circuitresistance,electrode,andmembranematerialhavebeenextensivelyinvestigated[3,4].However,inrecentstud-∗Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](B.Li).ies,oxygenreductionandelectronacceptanceinthecathodechamberhavebeenfoundasthelimitingstepforenergyproduc-tionduetotheslowreactionkineticsoftheoxygenreductionrate(ORR)[5,6].Platinum(Pt)hasbeenwidelyusedasthecathodecat-alysttoacceleratetheORRandelectronacceptanceinMFCs[7],butthehighcostofplatinumposesanobstacleintheapplicationofMFCs.Lowcostnon-PtcatalystsareneededtoreducethecostofMFCs.Iron(II)andcobalt-basedcathodeswerereportedtoshowsimilarperformancesasplatinum.Butlong-termstabilityofthesematerialsisnotsatisfied[8,9].Inthepastdecade,manganesedioxidehasbeenstudiedasapromisingalternativetoplatinuminmethanolandborohybridefuelcells[10,11].Catalystswithacryptomelane-typeoctahedralmolecularsieve(OMS-2)structurehavebeenofinterestascath-odecatalystsduetotheirexcellentsemi-conductivityandcatalyticactivityinORRs.Thereareonlyafewstudiesofapplyingman-ganeseoxideinMFCs.Zhangetal.reportedthat-MnO2isthemosteffectivecatalystamongthethreeOMSstructures(,,and-MnO2)duetoitshighestBrunauer–Emmett–Teller(BET)sur-faceareaandaverageoxidationstate(AOS:3.6)ofmanganese[12].Rocheetal.employedthemanganeseoxideasthecathodecatalyst,andobtainedthepeakpowerdensityof161mWm−2.Theyalsofoundthattheperformancesofmanganeseoxidecatalystswereeasilyimprovedbyoptimizingoperationconditions[13].Suibetal.reportedthatthetuningofAOSbytheincorporationofdif-0378-7753/$–seefrontmatter.PublishedbyElsevierB.V.doi:10.1016/j.jpowsour.2009.10.084X.Lietal./JournalofPowerSources195(2010)2586–25912587Fig.1.Thepossiblemechanismforoxygenreductionrate(ORR)withOMS-2cata-lysts.ferenttransitionalmetalionstoobtainanAOSof3.9–4.0couldgeneratethehighestreactionrateandcatalyticactivity[14].Syn-theticOMS-2showedoutstandingelectrochemicalandcatalyticpropertiesamongtheMnO2group;electronscouldeasilyflowinparticularOMS-2materials;anddopingofthesematerialscreateddifferencesofordersofmagnitudeinconductivity[15].Previou