Collecting the History of Molten Carbonate Fuel Cells

In a molten carbonate fuel cell (MCFC), carbonate salts are the electrolyte. Heated to 650 degrees C (about 1,200 degrees F), the salts melt and conduct ...       MoltenCarbonateFuelCells Technology History Applications Theessaybelow outlinesthetechnologyandhistoryofmoltencarbonatefuelcells.Ifyouhaveartifacts, photos,documents,orothermaterialsthatwouldhelptoimproveourunderstandingofthesedevices besuretorespondtothequestionnaire:   CollectingFuelCellHistory     MoltenCarbonateFuelCellTechnology Inamoltencarbonatefuelcell (MCFC),carbonatesaltsaretheelectrolyte. Heatedto650degreesC(about1,200degreesF),thesaltsmelt andconductcarbonateions(CO3)fromthecathodetotheanode. Attheanode,hydrogenreactswiththeionstoproduce water,carbondioxide,andelectrons.Theelectronstravelthroughanexternalcircuit,providingelectricalpoweralongtheway,andreturntothecathode. There,oxygenfromairandcarbondioxiderecycledfromthe anodereactwiththeelectronstoformCO3ionsthatreplenishtheelectrolyteand transfercurrentthroughthefuelcell.   Acomponentmodulefroma1966moltencarbonatefuelcellmadefortheU.S.Army High-temperatureMCFCscanextracthydrogenfromavarietyoffuelsusingeitheraninternalorexternalreformer.Theyarealsolessprone tocarbonmonoxide"poisoning"thanlowertemperaturefuelcells,whichmakes coal-basedfuelsmoreattractiveforthistypeoffuelcell.MCFCsworkwellwithcatalystsmadeofnickel,whichismuchlessexpensivethanplatinum. MCFCsexhibitupto60percentefficiency,andthiscanrise to80percentifthewasteheatisutilizedforcogeneration. Currently,demonstrationunitshaveproducedupto2megawatts(MW), butdesignsexistforunitsof50to100MWcapacity. Twomajordifficultieswithmoltencarbonatetechnologyputsitatadisadvantagecomparedtosolidoxidecells.Oneisthecomplexityofworkingwithaliquidelectrolyteratherthanasolid.Theotherstemsfrom thechemicalreactioninsideamoltencarbonatecell.Carbonateionsfromtheelectrolyte areusedupinthereactionsattheanode,makingitnecessarytocompensatebyinjectingcarbondioxide atthecathode. Top     MoltenCarbonateFuelCellHistory A100wattmoltencarbonatefuelcellmadefortheArmyaround1964 byTexasInstruments  Bothmoltencarbonateandsolidoxide fuelcellsarehigh-temperaturedevices.Assuch,thetechnicalhistoryofbothcells seemsrootedinsimilarlinesofresearch,withsignificantdivergenceappearing inthelate1950s. Inthe1930s,EmilBaurandH.PreisinSwitzerlandexperimentedwithhigh-temperature, solidoxideelectrolytes.Theyencounteredproblemswithelectrical conductivityandunwantedchemicalreactionsbetweenthe electrolytesandvariousgases(includingcarbonmonoxide).Thefollowingdecade,O.K. DavtyanofRussiaexploredthisareafurther,butwithlittlesuccess.By thelate1950s,DutchscientistsG.H.J.BroersandJ.A.A.Ketelaarbeganbuildingonthis previousworkanddecidedthatlimitationsonsolidoxidesatthattimemadeshort-term progressunlikely.Theyfocusedinsteadonelectrolytesoffused(molten)carbonatesalts. By1960,theyreportedmakingacellthatranforsixmonthsusinganelectrolyte"mixture oflithium-,sodium-and/orpotassiumcarbonate,impregnatedinaporoussintereddisk ofmagnesiumoxide."However,theyfoundthatthemoltenelectrolytewasslowlylost,partly throughreactionswithgasketmaterials.Aboutthesametime,FrancisT.Baconwasworking withamoltencellusingtwo-layerelectrodesoneithersideofa"freemolten" electrolyte.Atleasttwogroupswereworkingwithsemisolidor"paste"electrolytesandmostgroups wereinvestigating"diffusion"electrodesratherthansolidones. Inthemid-1960s,theU.S.Army'sMobilityEquipmentResearchandDevelopmentCenter(MERDC)atFt.BelvoirtestedseveralmoltencarbonatecellsmadebyTexasInstruments(seephotoabove).Theserangedinsizefrom100wattsto1,000wattsoutputandweredesignedto runon"combatgasoline"usinganexternalreformertoextracthydrogen.TheArmyespecially wantedtousefuelsalreadyavailable,ratherthanaspecialfuelthatmightbedifficulttosupplytofieldunits. Top     MoltenCarbonateFuelCellApplications Moltencarbonatefuelcellsdemandsuch highoperatingtemperaturesthatmostapplicationsforthiskindofcellarelimited tolarge,stationarypowerplants.Yetconsumersmightbenefitfromthistypeof cell,eveniftheyneverseeitintheirhomes.Thehighoperatingtemperatureopens theopportunityofusingwasteheattomakesteamforspaceheating,industrial processing,orinasteamturbinetogeneratemoreelectricity.Manymoderngas-fired powerplantsexploitthistypeofsystem,calledcogeneration. MC-PowermoltencarbonatefuelcellpowerplantatMiramar,1997   Intheearly1990s,IshikawajimaHeavy IndustriesinJapansuccessfullyoperateda1,000wattmoltencarbonatefuelcell powergeneratorfor10,000continuoushours.NowatleasttenJapanesecompaniesare workingonMCFCs.M-CPowerCorporationofIllinoisinstalleda250kwMCFCunitat theMiramarMarineCorpsAirStationinSanDiego(seephotoatleft)in1997.The fuelcellranbriefly,producingabout160mwhandgeneratingsteamforuseonthe base.Inspring1999,thecompanyinstalledanew75kwstackatMiramarandbegana testprogramintendedtograduallyscaleuptheinstallation--ultimatelyintendingto testa300kwprototypecommercialplant. In1996-97,FuelCellEnergyInc.(thenEnergyResearchCorp.)operateda2mw MCFCdemonstrationplantinSantaClara,California.The3,000-hourtestprogramwas cosponsoredbytheU.S.DepartmentofEnergyandtheelectricindustryresearchgroup EPRI.Thecompanyhopestoconstructunitsaslargeas3mw.Morerecently,Southern Co.,alargeelectricutility,announcedacooperativeprojectwithMercedesBenzUS Internationaltoconstructa250kwMCFCplantatMercedes'snewmuseumandvisitor centerinTuscaloosa,Alabama. Large,stationaryplantsliketheseholdthepromiseofreducingtheloadonAmerica's stressedtransmissiongrid.Placingpowerplantsnearerconsumers,aconceptcalled distributedgeneration,shouldimprovetransmissionreliabilityandefficiency—especially iftheplantsarecleanandquiet.Astheelectricindustryisderegulatedandutilities becomemorereluctanttoinvestinnewtransmissionlines,moltencarbonatefuelcellsmaycometoseemanincreasinglyattractiveoption. Top ©2001SmithsonianInstitution (CopyrightStatement)