外文翻譯--燃料電池及其發(fā)展前景.doc

文獻(xiàn)翻譯英文原文：FuelCellsandTheirProspectsAfuelcellisanelectrochemicalconversiondevice.Itproduceselectricityfromfuel(ontheanodeside)andanoxidant(onthecathodeside),whichreactinthepresenceofanelectrolyte.Thereactantsflowintothecell,andthereactionproductsflowoutofit,whiletheelectrolyteremainswithinit.Fuelcellscanoperatevirtuallycontinuouslyaslongasthenecessaryflowsaremaintained.Fuelcellsaredifferentfromelectrochemicalcellbatteriesinthattheyconsumereactantfromanexternalsource,whichmustbereplenished-athermodynamicallyopensystem.Bycontrastbatteriesstoreelectricalenergychemicallyandhencerepresentathermodynamicallyclosedsystem.Manycombinationsoffuelandoxidantarepossible.Ahydrogencelluseshydrogenasfuelandoxygen(usuallyfromair)asoxidant.Otherfuelsincludehydrocarbonsandalcohols.Otheroxidantsincludechlorineandchlorinedioxide.FuelcelldesignAfuelcellworksbycatalysis,separatingthecomponentelectronsandprotonsofthereactantfuel,andforcingtheelectronstotravelthoughacircuit,henceconvertingthemtoelectricalpower.Thecatalysttypicallycomprisesaplatinumgroupmetaloralloy.Anothercatalyticprocesstakestheelectronsbackin,combiningthemwiththeprotonsandoxidanttoformwasteproducts(typicallysimplecompoundslikewaterandcarbondioxide).Atypicalfuelcellproducesavoltagefrom0.6Vto0.7Vatfullratedload.Voltagedecreasesascurrentincreases,duetoseveralfactors:ActivationlossOhmicloss(voltagedropduetoresistanceofthecellcomponentsandinterconnects)Masstransportloss(depletionofreactantsatcatalystsitesunderhighloads,causingrapidlossofvoltage)Todeliverthedesiredamountofenergy,thefuelcellscanbecombinedinseriesandparallelcircuits,whereseriesyieldhighervoltage,andparallelallowsastrongercurrenttobedrawn.Suchadesigniscalledafuelcellstack.Further,thecellsurfaceareacanbeincreased,toallowstrongercurrentfromeachcell.ProtonexchangefuelcellsInthearchetypalhydrogenoxygenprotonexchangemembranefuelcell(PEMFC)design,aproton-conductingpolymermembrane,(theelectrolyte),separatestheanodeandcathodesides.Thiswascalledasolidpolymerelectrolytefuelcell(SPEFC)intheearly1970s,beforetheprotonexchangemechanismwaswell-understood.(Noticethatpolymerelectrolytemembraneandprotonexchangemechanismresultinthesameacronym.)Ontheanodeside,hydrogendiffusestotheanodecatalystwhereitlaterdissociatesintoprotonsandelectrons.Theseprotonsoftenreactwithoxidantscausingthemtobecomewhatiscommonlyreferredtoasmulti-facilitatedprotonmembranes(MFPM).Theprotonsareconductedthroughthemembranetothecathode,buttheelectronsareforcedtotravelinanexternalcircuit(supplyingpower)becausethemembraneiselectricallyinsulating.Onthecathodecatalyst,oxygenmoleculesreactwiththeelectrons(whichhavetraveledthroughtheexternalcircuit)andprotonstoformwaterinthisexample,theonlywasteproduct,eitherliquidorvapor.Inadditiontothispurehydrogentype,therearehydrocarbonfuelsforfuelcells,includingdiesel,methanol(see:direct-methanolfuelcellsandindirectmethanolfuelcells)andchemicalhydrides.Thewasteproductswiththesetypesoffuelarecarbondioxideandwater.Thematerialsusedinfuelcellsdifferbytype.Inatypicalmembraneelectrodeassembly(MEA),theelectrodebipolarplatesareusuallymadeofmetal,nickelorcarbonnanotubes,andarecoatedwithacatalyst(likeplatinum,nanoironpowdersorpalladium)forhigherefficiency.Carbonpaperseparatesthemfromtheelectrolyte.Theelectrolytecouldbeceramicoramembrane.OxygenionexchangefuelcellsInasolidoxidefuelcelldesign,theanodeandcathodeareseparatedbyanelectrolytethatisconductivetooxygenionsbutnon-conductivetoelectrons.Theelectrolyteistypicallymadefromzirconiadopedwithyttria.Onthecathodeside,oxygencatalyticallyreactswithasupplyofelectronstobecomeoxygenions,whichdiffusethroughtheelectrolytetotheanodeside.Ontheanodeside,theoxygenionsreactwithhydrogentoformwaterandfreeelectrons.Aloadconnectedexternallybetweentheanodeandcathodecompletestheelectricalcircuit.FuelcelldesignissuesCostsIn2002,typicalcellshadacatalystcontentofUS$1000per-kilowattofelectricpoweroutput.In2008UTCPowerhas400kwFuelcellsfor$1,000,000per400kWinstalledcosts.Thegoalistoreducethecostinordertocompetewithcurrentmarkettechnologiesincludinggasolineinternalcombustionengines.Manycompaniesareworkingontechniquestoreducecostinavarietyofwaysincludingreducingtheamountofplatinumneededineachindividualcell.BallardPowerSystemshaveexperimentswithacatalystenhancedwithcarbonsilkwhichallowsa30%reduction(1mg/cm2to0.7mg/cm2)inplatinumusagewithoutreductioninperformance.TheproductioncostsofthePEM(protonexchangemembrane).TheNafionmembranecurrentlycosts400/m.In2005BallardPowerSystemsannouncedthatitsfuelcellswilluseSolupor,aporouspolyethylenefilmpatentedbyDSM.Waterandairmanagement(inPEMFC).Inthistypeoffuelcell,themembranemustbehydrated,requiringwatertobeevaporatedatpreciselythesameratethatitisproduced.Ifwaterisevaporatedtooquickly,themembranedries,resistanceacrossitincreases,andeventuallyitwillcrack,creatingagasshortcircuitwherehydrogenandoxygencombinedirectly,generatingheatthatwilldamagethefuelcell.Ifthewaterisevaporatedtooslowly,theelectrodeswillflood,preventingthereactantsfromreachingthecatalystandstoppingthereaction.Methodstomanagewaterincellsarebeingdevelopedlikeelectroosmoticpumpsfocusingonflowcontrol.Justasinacombustionengine,asteadyratiobetweenthereactantandoxygenisnecessarytokeepthefuelcelloperatingefficiently.TemperaturemanagementThesametemperaturemustbemaintainedthroughoutthecellinordertopreventdestructionofthecellthroughthermalloading.Thisisparticularlychallengingasthe2H2+O2=2H2Oreactionishighlyexothermic,soalargequantityofheatisgeneratedwithinthefuelcell.Durability,servicelife,andspecialrequirementsforsometypeofcellsStationaryfuelcellapplicationstypicallyrequiremorethan40,000hoursofreliableoperationatatemperatureof-35Cto40C,whileautomotivefuelcellsrequirea5,000hourlifespan(theequivalentof150,000miles)underextremetemperatures.Automotiveenginesmustalsobeabletostartreliablyat-30Candhaveahighpowertovolumeratio(typically2.5kWperliter).HistoryTheprincipleofthefuelcellwasdiscoveredbyGermanscientistChristianFriedrichSchnbeinin1838andpublishedinoneofthescientificmagazinesofthetime.Basedonthiswork,thefirstfuelcellwasdemonstratedbyWelshscientistSirWilliamRobertGroveintheFebruary1839editionofthePhilosophicalMagazineandJournalofScience,andlatersketched,in1842,inthesamejournal.Thefuelcellhemadeusedsimilarmaterialstotodaysphosphoric-acidfuelcell.In1955,W.ThomasGrubb,achemistworkingfortheGeneralElectricCompany(GE),furthermodifiedtheoriginalfuelcelldesignbyusingasulphonatedpolystyreneion-exchangemembraneastheelectrolyte.ThreeyearslateranotherGEchemist,LeonardNiedrach,devisedawayofdepositingplatinumontothemembrane,whichservedascatalystforthenecessaryhydrogenoxidationandoxygenreductionreactions.Thisbecameknownasthe“Grubb-Niedrachfuelcell”.GEwentontodevelopthistechnologywithNASAandMcDonnellAircraft,leadingtoitsuseduringProjectGemini.Thiswasthefirstcommercialuseofafuelcell.Itwasntuntil1959thatBritishengineerFrancisThomasBaconsuccessfullydevelopeda5kWstationaryfuelcell.In1959,ateamledbyHarryIhrigbuilta15kWfuelcelltractorforAllis-ChalmerswhichwasdemonstratedacrosstheUSatstatefairs.Thissystemusedpotassiumhydroxideastheelectrolyteandcompressedhydrogenandoxygenasthereactants.Laterin1959,Baconandhiscolleaguesdemonstratedapracticalfive-kilowattunitcapableofpoweringaweldingmachine.Inthe1960s,PrattandWhitneylicensedBaconsU.S.patentsforuseintheU.S.spaceprogramtosupplyelectricityanddrinkingwater(hydrogenandoxygenbeingreadilyavailablefromthespacecrafttanks).UnitedTechnologiesCorporationsUTCPowersubsidiarywasthefirstcompanytomanufa