Assessment-ofthe-Internal-Resistance

AnUpflowMicrobialFuelCellwithanInteriorCathode:AssessmentoftheInternalResistancebyImpedanceSpectroscopy†ZHENHE,‡NORBERTWAGNER,§SHELLEYD.MINTEER,|ANDLARGUST.ANGENENT*,‡DepartmentofChemicalEngineeringandEnvironmentalEngineeringScienceProgram,WashingtonUniversityinSt.Louis,St.Louis,Missouri63130,InstituteforTechnicalThermodynamics,GermanAerospaceCenter,D-70569Stuttgart,Germany,andDepartmentofChemistry,SaintLouisUniversity,St.Louis,Missouri63103Anupflowmicrobialfuelcell(UMFC)systemwithaU-shapedcathodeinsidetheanodechamberwasdevelopedandproducedamaximumvolumetricpowerof29.2W/m3atavolumetricloadingrateof3.40kgCOD/(m3day)andanoperatingtemperatureof35°Cwhilefeedingsucrosecontinuously.TheCoulombicefficiencydecreasedfrom51.0%to10.6%withtheincreaseinthevolumetricloadingratefrom0.57to4.29kgCOD/(m3day).Inaddition,thelab-scaleUMFCmaintainedsolublechemicaloxygendemand(COD)removalefficienciesexceeding90%andvolatilefattyacidconcentrationsof∼40mg/L,indicatingefficientwastewatertreatment.Theanalysisofimpedancespectroscopy,generatedbyfittingexperimentaldataintoanequivalentcircuit,revealedthatatavolumetricloadingrateof3.40kgCOD/(m3day)theoverallinternalresistancewas17.13Ω.Thisinternalresistancewascomposedofelectrolyteresistance(8.62Ω),charge-transferresistance(7.05Ω),anddiffusionresistance(1.46Ω).Electrolyteresistancedominatedthroughouttheentirerangeofloadingrates.Inaddition,impedancespectroscopydemonstratedthatboththeanodicandthecathodiccharge-transferresistanceswereimportantlimitingfactors.TofurtherimprovethepoweroutputoftheUMFC,wemustreducetheelectrolyteresistancebyoptimizingreactorconfiguration,reducetheanodecharge-transferresistancesbyselectingsuperioranodicmicrobiota,andreducethecathodiccharge-transferresistancebyexploringsustainableandefficientcatalysts.IntroductionTheelectrochemicallimitationsontheperformanceofmicrobialfuelcells(MFCs)areduetotheinternalresistance(Ri),whichresultsfromohmic,kinetic,andtransportlimitations(1,2).ForMFCs,ohmiclimitationismostlyduetotheresistanceofele