清华大学博士论坛会议论文集10

1FiberGlassasSeparatorEnhancingthePerformanceofAir-CathodeSingle-ChamberMicrobialFuelCellsZHANGXiao-yuan1,CHENGShao-an2,WANGXin3,HUANGXia1,,LOGANBruce2,*(1.StateKeyJointLaboratoryofEnvironmentSimulationandPollutionControl,DepartmentofEnvironmentalScience&Engineering,TsinghuaUniversity,Beijing,100084P.R.China;2.DepartmentofCivil&EnvironmentalEngineering,PennStateUniversity,231QSackettBuilding,UniversityPark,PA16802,USA;3.StateKeyLaboratoryofUrbanWaterResourceandEnvironment,No73HuangheRoad,NangangDistrict,Harbin150090,China)Abstract:Microbialfuelcell(MFC)technologiesareapromisingapproachtowastewatertreatmentasthetreatmentprocesscancapturebioelectricity,andair-cathodesingle-chamberMFCshavepotentialforpracticalapplication.Oneofthemainchallengesisthatthecoulombicefficiency(CE)isrelativelylowcomparedwithMFCcontainingamembrane.Inthisstudy,fiberglasswasappliedasaseparatorinsingle-chamberMFCsystemstoenhancetheperformance.TheMFCwithfiberglassoncathodesideand2cmelectrodedistanceobtainedaCEof82.6%,increasedby136%comparedwiththatwithoutaseparator(35.0%)atthesamecurrentdensityof2.68A/m2.SimilarCEperformancewasachievedinseparatorelectrodeassembly(SEA)MFC,wherethefiberglasswassandwichedbetweentheanodeandcathode,incomparisontothatwith2cmelectrodespaceandfiberglassoncathodeside.AdoubleSEAMFCwasalsoconstructedtoincreasetheelectrodearea,whichhadpairsofelectrodes2cmapart,andamaximumpowerdensityof57.5W/m3wasobtained,whichisanincreaseofmorethan60%comparedtothoseofseparator-freeandfiberglassoncathodesidewith2cmelectrodespaceMFCs(35.6W/m3and34.7W/m3respectively).Thisstudyindicatesthattheperformanceofair-cathodesingle-chamberMFCscouldbeimprovedsignificantlyusingaproperseparator.Keywords:microbialfuelcell(MFC);separator;fiberglass;coulombicefficiency(CE);powerdensityIntroductionMicrobialfuelcells(MFCs),whichcangenerateelectricityfrombiomassusingbacteria(Logan,2008),areconsideredtobeapromisingtechnologyforwastewatertreatmentandhavedrawnincreasingattention(Lovley,2008).Single-chamberair-cathodeMFCshavepotentialforpracticalapplication(Fanetal.,2007):reactantoncathodesideispassiveairwithoutenergyconsuming,suchasaeration;productoncathodesideiswaterandnochemicalregenerationisneeded;thedesignandoperationsaresimple.Inair-cathodeMFCinabsenceofmembrane,relativelyhighpowerdensitycanbeachieved.Forfurtherincreasingtheperformances,thereareseveralmainchallenges:thecoulombicefficiency(CE,recoveryofelectronsfromsubstrate)arestilllowduetotheoxygendiffusionfromcathodetothereactor;thedistancebetweenanodeandcathodeelectrodecouldnotbefurtherdeceasedtoreducetheinternalresistanceduetotheoxygendiffusionandtheriskofshortcircuit(Chengetal.,2006a).Separatorcanbeappliedinair-cathodesingle-chamberMFCsystemtoovercomethesetwochallenges.Fanetal.(2007)placedaJ-Clothasaseparatortoenhancetheperformance.However,J-Clothisbiodegradable.Inthisstudy,fiberglass,non-biodegradablematerialwasusedasseparatorindifferentconfigurationsandtheCEsandpowerdensitieswereenhanced.1Materialsandmethods1.1MFCreactorsAnodeswereammoniagastreated(Chengetal.,2007)carboncloth(E-Tek,TypeA,nonwetproofing,BASFFuelCell,Inc.NJ)with7cm2projectedarea.Cathodesweremadeofcarboncloth(E-Tek,TypeB,30%wetproofing,BASFFuelCell,Inc.NJ)with0.5mg/cm2Platinumon7cm2projectedareaand4PTFEdiffusionlayerstopreventwaterloss(Chengetal.,2006b).Fourtypeconfigurationsofsingle-chamberair-cathodecubic-shapedMFCreactorswereconstructedbasedonpreviouslydescribedconfigurations(Chengetal.,2006a;Liangetal.,2007;Fanetal.,2007)(Fig.1).Theseparator-freeMFC,withtheanodeandcathodespaced2-cmapartCorrespondingauthor:E-mail:[e-mail]@psu.edu2(NS)wasstudiedasa“control”.Thisdesignwasmodifiedbyplacingafiberglass(ChinaYangzhouGuotaiFiberglassCo.,LTD)asaseparatoragainstthecathode,whilemaintainingthe2cmelectrodespacing(S).ThethirdtypeofMFCwasasingleseparatorelectrodeassembly(SSEA),wheretheseparatorwassandwichedbetweentheanodeandcathodeplacedonthesamesideofthereactor.TheliquidvolumesoftheNS,SandSSEAreactorswere12mL.ThefinaltypereactorwasdoubleseparatorelectrodeassemblyMFCswithtwoSEAs(oneoneachside),witha2cmspacingbetweentheelectrodes(DSEA,9mLliquidvolume).AllanodeswereenrichedinNS-typeMFCsusingsuspendedbacteriafromanMFC(originallyinoculatedwithprimaryclarifieroverflow)thathadbeenoperatedinfedbatchmodeforoveroneyear.Thereactorswerefeda1g/Lofacetatein50mMPBSmediumcontainingmineral(12.5mL/L)andvitamin(5mL/L)solutions.FollowingoperationoftheNSMFCsformorethan20cycles,wheretheyallexhibitedstableandparallelperformance,theanodeswerethenusedinthedifferentMFCdesignsdescribedabove.AllMFCswereoperatedunderambienttemperatureconditionsinthelaboratory(23±3ºC).1.2AnalysesVoltage(E)acrosstheexternalresistorintheMFCcircuitwasmeasuredusingadataacquisitionsystem(2700,KeithleyInstrument,OH)connectedtoapersonalcomputerat20mininterval.Current(I=E/R),power(P=IE),coulombicefficiency(CE)werecalculatedaspreviouslydescribed(Loganetal.,2006),withthecurrentdensityandpowerdensitynormalizedbytheprojectedsurfaceareaofcathode,andvolumetricpowerdensitynormal