Reversible energy storage on a fuel cell-supercapacitor hybrid device [Elektronische Ressource] / vorgelegt von / Jesus Enrique Zerpa Unda

Description

REVERSIBLE ENERGY STORAGE ONA FUEL CELL-SUPERCAPACITORHYBRID DEVICEVon der Fakult at Chemie der Universit at Stuttgart zurErlangung der Wurde eines Doktors der Naturwissenschaften(Dr. rer. nat.) genehmigte Abhandlungvorgelegt vonJesus Enrique Zerpa Undaaus Caracas, VenezuelaHauptberichter: Prof. Dr. Emil RodunerMitberichter: Prof. Dr. Klaus MullerTag der mundlic hen Prufung: 18.02.2011Institut fur Physikalische Chemie der Universit at StuttgartNovember 2010Gedruckt mit Unterstutzung des Deutschen AkademischenAustauschdienstesEidesstattliche ErklarungIch versichere, dass ich diese Dissertation selbstst andig verfasst und nur die angege-benen Quellen und Hilfsmittel verwendet habe.Jesus Enrique Zerpa Unda23.11.2010Prufunsv orsitzender: Prof. Dr. Michael R. BuchmeiserHauptberichter: Prof. Dr. Emil RodunerMitberichter: Prof. Dr. Klaus MullerTag der mundlic hen Prufung: 18.02.2011ContentsContents 71 Introduction 92 Fundamentals 112.1 Fuel cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.1.1 Types of fuel cells . . . . . . . . . . . . . . . . . . . . . . . . . 112.1.2 Polymer electrolyte membrane fuel cells . . . . . . . . . . . . . 122.1.3 Fuel cell polarization curves . . . . . . . . . . . . . . . . . . . 162.2 Electrochemical supercapacitors . . . . . . . . . . . . . . . . . . . . . 182.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182.2.2 The electrochemical double layer .

Informations

• Publié par: universitat_stuttgart
• Publié le: 01 janvier 2011
• Nombre de lectures: 45
• Poids de l'ouvrage: 10 Mo

Extrait

REVERSIBLEENERGYSTORAGEON

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CAPCELL-SUPERFUELCITORA

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Hauptberichter:Prof.Dr.EmilRoduner
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Tagderm¨undlichenPr¨ufung:18.02.2011

Institutf¨urPhysikalischeChemiederUniversit¨atStuttgart
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11talsundamenF22.1Fuelcells..................................11
2.1.1Typesoffuelcells.........................11
2.1.2Polymerelectrolytemembranefuelcells.............12
2.1.3Fuelcellpolarizationcurves...................16
2.2Electrochemicalsupercapacitors.....................18
2.2.1Introduction............................18
2.2.2Theelectrochemicaldoublelayer................21
2.2.3Carbonmaterialsforelectrochemicalcapacitors........26
2.2.4Experimentalevaluationofelectrochemicalcapacitors.....34
2.3Hybridsystemsinvolvingsupercapacitors................38
2.4Thenewconcept.............................41

3Experimentaltechniques47
3.1Supercapacitor-typeelectrodematerial.................47
3.2Catalystcoatedmembranepreparation.................47
3.2.1Catalystink............................47
3.2.2Membranepretreatment.....................48
3.2.3Spray-coatingmethod......................48
3.3Two-electrodefuelcell-supercapacitorhybridcell...........49
3.3.1Supercapacitor-typeelectrodepreparation...........50
3.3.2Electrochemicalmeasurementsofthetwo-electrodehybridcell50
3.4Three-electrodefuelcell-supercapacitorhybridcell...........51
3.4.1Supercapacitor-typeelectrodepreparation...........52
3.4.2Electrochemicalmeasurementsofthethree-electrodehybridcell52

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4Experimentswiththetwo-electrodefuelcell-supercapacitorhybrid
59cell4.1Carbonmaterialcharacterization....................59
4.2Charging-dischargingexperimentsusingwater.............63
4.2.1Results...............................63
4.2.2Discussion.............................68
4.3Effectoftheelectrolyteonthecharging-dischargingcurves......76
4.3.1Results...............................76
4.3.2Discussion.............................77
4.4Estimationoftheelectricalcapacitance.................84
4.4.1Results...............................84
4.4.2Discussion.............................86
4.5Summary.................................90
5Experimentswiththethree-electrodefuelcell-supercapacitorhy-
93cellbrid5.1Operationasafuelcell..........................93
5.1.1Results...............................93
5.1.2Discussion.............................94
5.2Operationasasupercapacitor......................97
5.2.1Results...............................97
5.2.2Discussion.............................99
5.3Operationasahybriddevice.......................104
5.3.1Results...............................104
5.3.2Discussion.............................108
5.4Summary.................................114
6Finalsummaryandconclusions117
123Zusammenfassung7129tswledgmenknoAc131yBibliograph8

ductiontronI1

Energyhasplayedadeterminantroleinthedevelopmentofthehumansocietyby
allowingittoadaptandcontroltheenvironment.Inanyfunctionalsocietytheman-
agingofenergyisessential,forexample,intheindustrializedworldtheavailability
ofenergyresourcesisessentialassupportforcriticalsectors,suchasagriculture,
transportation,wastecollection,informationtechnologyandcommunication.One
ofthemostimportantenergyresourcesarethefossilfuels,sincetheyprovidemore
than80%oftheenergyconsumedinthepresenttime[1].Theincreasinguseofthese
typesoffuelsasenergyresourcesincetheIndustrialRevolutionhasbeenrelated
withseriousenvironmentaleffects,suchasglobalwarmingasaconsequenceofthe
highamountofgreenhousegasemissionscomingformthecombustionofsuchfuels
[2].Specificallyinthetransportationsector,fossilfuelshavebeenwidelyutilizedas
energycarriersresultinginanimportantglobalcontributiontothesegreenhouse
gasemissionsandpollutants.
Theuseofotherenergycarrierswhichproducealowerlevelofpollutantsand
suchgasemissionsisanalternativetolowertheenvironmentaleffects.Hydrogen,for
example,hasemergedasoneofthemostpromisingcandidatesforthereplacement
ofthecurrentfossil-fuel-basedenergycarriers.Lowmassdensity,highabundance,
anditsenvironmentalfriendlinessmakeitanattractivefuelforvariousapplications
[3],butanimportantconditionforitswideusageformobileapplicationsisthe
developmentofasafe,cheapandsimplestoragemethod.Hydrogenstoragehas
beentermed“TheGrandChallenge”[4],asthecommerciallyavailableoptions,
suchasstoringhydrogengasinhighpressuretanksmadeofcompositematerials
orsteelandstoringitasaliquidincryogenicvessels,eitherrequirehighpressure
orlowtemperature(orboth)forstorage,orhightemperatureforreleaseofH2,
ortheyrequireelectricalwork[5].Theseoptionsconsumeasubstantialfraction
ofthestoredenergyandmayhaveproblemswithreversibility[3,6],forexample,
theenergynecessaryforliquefactionofthehydrogenatlowtemperaturesrepresents
almosthalfofthelowerheatingvalueofhydrogencombustion[7].Therefore,itwould
beofgreatadvantagetodevelopahydrogenstoragesystemthatcanbereversibly
loadedandunloadednearambienttemperatureandpressure,perhapssimplyby

9

openingavalveorclosingaswitch.
Fuelcellsareenergyconverterdevicescharacterizedbyhavingahighspecific
energyandofferinganaveragepoweroutput.Thisfeatureisveryimportantforthe
applicationswhen,forexample,avehiclepoweredbyafuelcellhastomaintain
aconstantvelocityorwhenacomputerisrunningroutineprocesswhichdonot
involveahighpowerdemandinashorttime.However,instantaneoushighpower
demandcycles,suchasdrivingup-hilloracceleratingthevehicleafterbeingstopped
atthetrafficlightsorinalaptopwhenaCDhastobewrittenorduringstart-upare
commonsituationsinthenormaloperationofthesedevices.Therefore,itwouldbe
alsonecessarytoconsiderasystemcapableofstoringenergyandofdeliveringitas
ahighspecificpowerinashorttime,suchasasupercapacitor,inordertoimprove
theefficiencyofthefuelcellsystem.Consequently,anenergysystemwhichcouples
thehighenergydensityoffuelcellswiththerapidcharge/dischargeandpower
capabilitiesofsupercapacitorsisdesired.Recently,increasingeffortsaredevotedto
thehybridizationoffuelcellsorbatterieswithsupercapacitors.
Inthepresentworkweexplorethepotentialandlimitationofanovelconcept
ofenergystoragebasedonhydrogen,theprincipaladvantageofthisnovelhybrid
deviceisthatitworksspontaneously(withoutapplyinganycurrentorvoltage)and
reversiblynearambientpressureandtemperature.Inthisconceptprotonsandelec-
tronsarefirstlyelectrochemicallyseparatedatafuelcellanodeandthenstoredinthe
electricaldoublelayerofasupercapacitor.Webeganbyinvestigatingacompletely
unexploredfuelcell-supercapacitorhybridconfigurationbasedonthecombination
ofafuelcell-typeFaradaicelectrodecoupledinternallywithasupercapacitor-type
non-Faradaic(alsopseudo-Faradaic)electrodeinatwo-electrodesingle-cellarrange-
ment.Thiscellwasdesignedinordertotestthebasicconceptandtostudythe
influenceofseveralvariablesonitsperformance,namelythetypeofthestorage
material,theresponsetothepHandconcentrationoftheelectrolyte,theinfluence
oftheH2pressureandthecharginganddischargingkinetics.Anadvancedde-
signofthiscellinvolvingthecombinationofanon-Faradaic(alsopseudo-Faradaic)
supercapacitor-typeelectrodewithtwofuelcell-typeelectrodesinasinglecellcon-
figurationwastested.Theresultsrevealedthattheconceptisviable,offeringaway
tostorehydrogen(energy)reversiblyandatnearambienttemperatureandpressure
andthatitisalsoabletoactasahydrogenbufferinafuelcell-supercapacitorhybrid
configuration.

10

talsundamenF2

cellsuelF2.1

Afuelcellisanelectrochemicaldevicewhichconvertsdirectlychemicalenergyof
afuelintoelectricalenergyinformofDCcurrent.Thisconversionofenergytakes
placeverysimplyincomparisonwiththetypicalprocessofelectricitygeneration
fromfuels,whichnormallyinvolvesseveralconversionstepswithlossesofenergy
presentineachstep.Afuelcellgenerateselectricityinonesinglestepandwithout
anymechanicallosses.Alsotheefficiencyofsuchadeviceisremarkablyhigherthan
thetypicalprocessofelectricitygenerationfromfuels,suchastheCarnotprocess.
Furthermore,withtheuseofenvironmentallyfriendlygeneratedfuels,thiskindof
devicescouldproduceneartozeroemissionsandcontaminants.Itssimplicity,high
efficiencyandenvironmentalfriendlinessarethemostattractivefeaturesthathave
madethefuelcelltobeconsideredasoneofthecandidatesforafutureenviron-
mentallysustainableenergyconversionsystem.

2.1.1Typesoffuelcells
Commonly,fuelcellsaregroupedbythetypeofelectrolytetheyuse,namely[8]:

-AlkalinefuelcellsuseconcentratedKOH(50wt.%-85wt.%)aselectrolyte,
andtheoperationtemperatureisintherangeof120-250◦C.Theelectrolyteis
retainedinamatrix,suchasasbestos.Theelectrocatalystsu