121012磁场强度小论文.docx

121012磁场强度小论文.docx

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121012磁场强度小论文

AnalysisofElectricityProductionandElectrochemicalImpedanceSpectroscopyofMicrobialFuelCellunderDifferentIntensityofStaticMagneticField

ABSTRACT

Two-chambermicrobialfuelcells（MFC）wereloadedwithstaticmagneticfield（MF）,whichisof0mT,100mT,200mTand300mTrespectively.TheelectricityproductionofMFCunderMFwasinvestigatedbyelectrochemicalmethods.Theresultsshowedthatthestart-upperiodofMFCswithMFwasshorterthanMFCwithoutMF.MFCwith100mTneededtheshortesttimeof7daystoobtainthestablevoltageoutput.ThemaximumpowerdensityofMFCwith200mTwas1.56W/m2,whichwasthebestperformanceamongtheMFCs.TheimpactofMFonthechargetransferresistances（Rct）ofanode,cathodeandwholeMFCwereanalyzedbyelectrochemicalimpedancespectroscopy（EIS）.Thisstudydevelopedanewmethodtoestablishtheequivalentcircuit（EC）modeltothewholeMFCbyconnectingthemodelsofanodeandcathodeinseries.ThesimulatedresultsshowedthatanodeRctweremuchhighercomparedtocathode.ThecellRctandtheanodeRctofMFCwith200mTreducedby56.6%and57.2%respectivelycomparedtoblankreactor.ThestaticMFresultedinthedecreaseofanodeRct,andthusreducedtheoverallcellRct.ButtherewasabestfieldrangefortheimpactofMFonthemicroorganisms.

INTRODUCTION

Thetechnologyofmicrobialfuelcell（MFC）cantakeadvantageofbiodegradablematerialinorganicwastewaterforenergyrecovery.1MFCsovercometheinherentshortcomingsoftraditionalbiologicalwastewatertreatment,whichmaybeabletomitigatewaterpollutionandenergyshortageproblemtoacertainextenttoday.MFCs,whichareconsideredtobeanattractivebiofuel,haveattractedtheattentionofuniversities,corporationsandgovernmentdepartments.ButthepoweroutputofMFCsistoolowatpresent,whichcan'tmeettheneedsofwastewatertreatmentfacilities’powersupply.ManyresearchersareworkingtoimprovepoweroutputandelectricityproductionefficiencyofMFCthroughavarietyofmethods,suchaslookingforefficientexoelectrogens,2modifyingelectrodematerials,3improvingcellconfiguration4andapplyingphysicalfield5.

Recently,theeffectofmagneticfieldontheelectricityproductionofMFCisgraduallyattractingtheinterestofresearchers.Ithasbeenprovedthatmagneticfieldcancauseaseriesofbiologicalreactionsinmicroorganisms.6,7Magneticfieldcanaffectthecharacteristicsoftheenzyme,DNAandbiofilm,thusaffectingtheorganism'smetabolism.8,9Theapplicationofmicroorganismmagneticeffectinwastewaterbiologicaltreatmenthasbeenwidelyreported.Lietal.foundthat100mTMFpromotedelectricityproductionofShewanella-inoculatedMFC,andMFCmaximumvoltageincreasedby20%-27%.5TheimprovementinelectricityproductionofMFCsunderMFexposurewasmainlyattributedtotheenhancedbioelectrochemicalactivity,possiblythroughtheoxidativestressmechanism.

Electrochemicalimpedancespectroscopy（EIS）isakindofelectrochemicalmeasurementmethodwithsmallamplitudeofsinewavepotential（orcurrent）asdisturbancesignal.10Atpresent,EISisapowerfultoolappliedtotheMFCresearch.11-13Itnotonlycanmeasurethecellinternalresistance,moreimportantly,butalsodistinguishthreepartsofinternalresistance:

ohmicresistance,chargetransferresistanceanddiffusionresistance.14Inaddition,EIScanstudytheelectrochemicalbehavioroftheredoxmediatorsecretedbybacteriainMFC.15ThegreatestfeatureoftheEISusedinMFCresearchisnointerruptionandinterferenceinthetestingprocesstothereactorsandmicrobialcultivation.

ButatpresenttherearetwoproblemsfortheapplicationofEISintheresearchofMFC.First,thefrequencyrangeisn’tverycertain,whichisdifferentinvariousresearchs.16,17Generally,theimpedancevalueathighfrequencyrepresentsohmicresistance,andtheimpedancevalueatlowestfrequencyisthetotalresistance.18Therefore,differentmeasurementfrequencywillimpactdeterminationofinternalresistance.Second，althoughthereisabasicformastheEISequivalentcircuit（EC）,thatisnotsufficientfordifferentMFCsystems.14ThedifferencesofthestructureandmaterialswillbereflectedinEISresults.Sometimes，thefittingresultsfortheimpendenceresultsisn’tgoodduetoapplicationofthebasicfittingmodel.11Inaddition,theuseofbasicmodelcannotprovidecompleteanalysisoftheanodeandcathodeimpedance.Basedonaboveopinion,EISisusedtostudytheelectrochemicalbehavioroftheMFCanode,cathodeandthewholecellinourresearch.ThisisnotonlytofindnewwaytoestablishasuitableequivalentcircuitforMFC,butalsotoanalyzetheimpactofmagneticfieldontheeachcomponentofMFCbyfittinganodeandcathodeimpedanceresults.

Inthisstudy,theelectricityproductionofsewageinoculatedtwo-chambermicrobialfuelcellsunderdifferentMFintensitywasinvestigated.ItmayoffervaluablereferencesforindustrialapplicationofmagneticfieldpromotingMFCelectricityproductioninwastewatertreatment.

MaterialsandMethods

MFCconfigurationandoperation

Two-chamberMFCswereconstructedwithcarboncloth（XinkaCarbonTechnologyCo.,Ltd.,Shanghai,China）asanodeandcathode.Theanodeandcathodechamberwereplexiglasscylinder（φ4×6cm,emptybedvolumeofapproximately75mLeach）adjoinedbytheflangewhichcontainedtheprotonexchangemembrane（NafionTM117,DupontCo.,Delaware,USA）.Theelectrodes（2.5×2.5cm，6.25cm2）wereconnectedbytitaniumwirewiththedistanceofapproximately9cm.Fourreactorsweresetupfortheexperiments,MFC0,MFC1,MFC2andMFC3representtheMFCwith0mT,100mT,200mTand300mTMFrespectively.ThemagnetswereboundontotheexternalwallsofanodechamberstoobtainspecificMFintensitiesattheanodeposition.

Fig.1SchematicdiagramofMFCexperimentalinstallation

TheMFCswereinoculatedwithmixture（50/50v/v）ofequalizationtankeffluent（ecust,Shanghai,China）withaphosphatebuffersolution（PBS,50mM）containing1g/Lsodiumacetateandmineralsolution（12.5/1000v/v）19.Thecatholyteconsistedof0.1mMK3Fe（CN）6ina50mMphosphatebuffersolution.Theanolyteandcatholytewerekeptinthe1LbrownreagentbottleandcontinuouslyrecirculatedtotheMFCcompartmentsbyaperistalticpump（BT100-1L,LongerPrecisionPumpCo.,Baoding,China）ataflowrateof2mL/min.Sodiumacetateof1gwasaddedtotheanolytebottleeverytwodaysasacycle,andtheanodicandcathodicsolutionwasreplacedeveryweek.Electricitygenerationexperimentswereconductedunderambienttemperature.

MFCsAnalysis

ThepolarizationandpowerdensitycurvesweredeterminedbylinearscanningtoinvestigatetheinfluenceonenergyefficiencyofMFCsexposedtomagneticfield.Linearscanningmethodadoptedtwo-electrodesystem,wherecathodewasusedasworkingelectrodeandanodeasreferenceelectrodeandcounterelectrode.ThecircuitsweredisconnecteduntiltheMFCvoltagestabilizedtotheopencircuitvoltage（OCV）,andthentheMFCswerescannedfromOCVto10mVwiththescanningrateof1mV/s.VoltageUandcurrentI　wererecordedtoobtainthepolarizationcurves.ThepowerdensitywerecalculatedaccordingtotheequationP=U×Itodrawpowerdensitycurves.

Electrochemicalimpedancespectroscopy（EIS）wascarriedoutbyanelectrochemicalworkstation（PARSTAT2273,PAR,USA）.Thetwo-electrodemodewasusedtoanalyzethewholecell.Theanodewasusedastheworkingelectrode,whilethecathodeasthecounterelectrode.Thethree-electrodemodewasusedtoanalyzetheindividualelectrode.Theexaminedelectrodewasusedastheworkingelectrode,whiletheotherelectrodeasthecounterelectrode.Thesaturatedcalomelelectrode（SCE）wasusedasthereferenceelectrodethatplacedintheexaminedcompartment.14ImpedancemeasurementswereconductedattheOCVofMFCsoverafrequencyrangeof100KHzto1mHz.TheNyquistplotsoftheimpedancespectrawereanalyzedbyZsimpwin3.10（EchemSoftware）.

ResultsandDiscussion

MagneticfieldontheeffectofMFCstartup

Fig.2Cellvoltagechangeduringthestart-upperiod

Figure2reflectsthevoltagechangefromstarttothestableoperation.Thetrendsofthecurvesareconsistentwiththegeneralruleofthemicrobialfuelcellstartup.Thepeaksofthecurvesindicatetheopencircuitvoltagewhichmeasuredbymultimeter（MY61,ShanghaiYihuaV&AinstrumentCo.,Ltd.,China）.MFC1startedthefastestwith100mTMF,whichbegantoappearvoltagesuddenchangeatday6,andfinishedstartupatday7.Then,MFC2with200mTandMFC3with300mTappearedvoltagejumpalmostonthe7thday，andcompletedstartuponthe10thday.VoltageofMFC0withoutMFbegantoincreasesharplyatday9,andachievedstabilityatday11.Theseresultsshowthatthemagneticfieldpromotedtheenrichmentoftheanodeelectrogenesis,acceleratedtherateoftheirproliferation.Itissupposedthattheroleofmagneticfieldistoreducetheanodeactivationloss,whichisduetomicrobialmetabolismandelectrochemicalreaction.

Polarizationandpowerdensitycurves

Fig.3PolarizationcurvesofMFCs

Fig.4PowerdensitycurvesofMFCs

PoweroutputandpolarizationcurveswereexaminedasshowninFig.3andFig.4.InFig.3,withtheincreaseofcurrentdensity,thecellvoltagedecreased.MFCpolarizationincludesanodepolarization,cathodepolarization,membraneandelectrolytepolarization.18DuetothesameelectrolyteandMFCconstruction，theMFCpolarizationcurvecouldreflecttheperformanceofanodeelectricalproduction.Fromthepolarizationcurves,itcanbefoundthattheopencircuitvoltageofthereactorsunderMFishigherthanthevalueofMFC0w