质子交换膜燃料电池氧电极有序稳定结构的构筑及耐久性研究

质子交换膜燃料电池氧电极有序稳定结构的构筑及耐久性研究摘要

质子交换膜燃料电池是目前最为成熟的可再生能源转化装置，其氧还原反应（ORR）是电极反应的重要环节。然而，质子交换膜燃料电池中氧还原反应的影响因素较多，导致其效率和耐久性不尽如人意。本文围绕质子交换膜燃料电池氧电极的有序稳定结构，从结构优化及稳定性角度，开展了一系列的研究。首先，探究了有序结构对ORR的催化作用及电化学性能的影响，发现超晶格纳米孔结构的氧电极具有较好的活性和稳定性。同时，研究了材料表面的交换作用对燃料电池性能的影响，发现表面功能化可以有效提高氧电极的催化性能。最后，分析了氧电极在长时间运行过程中的耐久性问题和降解机理，并提出相应解决方案。

关键词：质子交换膜燃料电池；氧还原反应；有序稳定结构；纳米孔；表面功能化；耐久性

Abstract

Protonexchangemembranefuelcell(PEMFC)iscurrentlythemostmaturerenewableenergyconversiondevice,andoxygenreductionreaction(ORR)isanimportantpartofelectrodereactionsinPEMFC.However,thefactorsaffectingtheORRinPEMFCsarediverse,leadingtopoorefficiencyanddurability.ThispaperfocusesontheorderedstablestructureoftheoxygenelectrodeinPEMFCsandconductsaseriesofstudiesfromtheperspectivesofstructuraloptimizationandstability.Firstly,weinvestigatedthecatalyticeffectoforderedstructuresonORRandtheelectrochemicalperformance,andfoundthattheoxygenelectrodewithsuperlatticenanoporousstructurehasgoodactivityandstability.Simultaneously,theeffectofsurfaceexchangeontheperformanceoffuelcellswasstudied,anditwasfoundthatsurfacefunctionalizationcaneffectivelyimprovethecatalyticperformanceoftheoxygenelectrode.Finally,thedurabilityproblemanddegradationmechanismoftheoxygenelectrodeduringlong-termoperationwereanalyzed,andcorrespondingsolutionswereproposed.

Keywords:protonexchangemembranefuelcell;oxygenreductionreaction;orderedstablestructure;nanopore;surfacefunctionalization;durabilitProtonexchangemembranefuelcells(PEMFCs)havebeenrecognizedasapromisinggreenenergytechnologyduetotheirhighenergyconversionefficiency,lowoperatingtemperature,andzero-emissionnature.However,thesluggishkineticsoftheoxygenreductionreaction(ORR)atthecathodeisstillalimitingfactorfortheircommercialization.

OneeffectivestrategytoenhancetheORRperformanceistoengineerthecathodecatalystlayerwithanorderedstablestructurefeaturinghighsurfaceareaanduniformporesizedistribution.Forinstance,theuseofmesoporouscarbonmaterialssuchasSBA-15andMCM-41asasupportforplatinum(Pt)catalysthasbeenreportedtosignificantlypromotetheORRkineticsbyfacilitatingoxygendiffusionandminimizingmasstransportlimitations[1].

AnotherapproachtoimprovetheORRactivityistofunctionalizethesurfaceoftheelectrocatalystwithcertaingroupsthatcanfacilitatetheadsorptionanddissociationofoxygenspecies.Forexample,nitrogen-dopedcarbonhasbeenusedasapromisingalternativetoPtduetoitshighstabilityandexcellentORRperformance,whichcanbeattributedtothechemisorptionofoxygenonthenitrogen-dopedsites[2].

Besides,thelong-termdurabilityofthePEMFCcathodeisofgreatconcern,astheORRprocesscanbeaccompaniedbytheformationofreactiveoxygenspeciesthatcausedegradationofthecatalystlayer.Tomitigatethisissue,somestrategieshavebeenproposed,suchasoptimizingthewatermanagementtopreventmembranedehydration,reducingtheoperatingtemperaturetominimizetheriskofcarboncorrosion,andapplyingprotectivecoatingstoimprovetheoxidativestabilityofthecatalystlayer[3].

Inconclusion,theORRperformanceofPEMFCcathodescanbeimprovedbytailoringthecatalyststructureandsurfacechemistry.Meanwhile,acomprehensiveunderstandingofthedegradationmechanismsandcorrespondingmitigationmeasuresisalsocrucialforthesustainableoperationofthefuelcellsystemOnepotentialapproachtofurtherimprovetheORRperformanceofPEMFCcathodesistoenhancethemasstransportofreactantsandproductswithintheelectrode.Thiscanbeachievedbyoptimizingtheelectrodemicrostructure,suchastheparticlesize,porosity,andtortuosity,aswellastheionomercontentanddistribution.Forinstance,increasingtheionomercontentcanimprovetheprotonconductivitywithintheelectrode,leadingtoenhancedelectrochemicalactivityanddurability[25].Moreover,theuseofnanostructuredcatalysts,suchasPt-basednanoparticles,canincreasetheactivesurfaceareaandfacilitatemasstransportbyreducingthediffusionlengthofreactantsandproducts[26].However,carefulcontroloftheparticlesizeanddistributionisnecessarytopreventagglomerationanddeactivationofthecatalyst[27].

AnothercrucialaspectofPEMFCcathodedesignistheintegrationwithothercomponentsofthefuelcellsystem,particularlythemembraneandanode.BecausetheORRreactionatthecathodeconsumesprotonandelectroncarriersgeneratedbythehydrogenoxidationreactionattheanode,theperformanceanddurabilityofthecathodearecloselycoupledwiththoseoftheanode.Therefore,optimizingtheanodecatalystandmicrostructure,aswellasthemembraneproperties,cansignificantlyimpacttheoverallfuelcellperformance[28,29].Forinstance,usingPtRualloyastheanodecatalystcanenhanceitsactivityandselectivitytowardshydrogenoxidation,whilemaintainingagoodCOtolerance[30].Additionally,increasingthemembranethicknessandreducingitsresistancecanimprovetheionicconductivityandreducethecrossoverofreactantgases,leadingtoenhancedcathodeperformance[31].

Overall,thedevelopmentofhigh-performanceanddurablePEMFCcathodesrequiresamultidisciplinaryapproachthatintegratesmaterialsscience,electrochemistry,transportphenomena,andsystemengineering.WhilesignificantprogresshasbeenmadeinunderstandingtheORRmechanism,optimizingthecatalyststructureandsurfacechemistry,andmitigatingdegradation,therearestillmanychallengesandopportunitiesforfutureresearch.Forinstance,thedevelopmentoflow-costandabundantnon-noblemetalcatalysts,aswellastheexplorationofnewmaterialsforthecatalystsupportandmembrane,canfurtherimprovetheperformanceandsustainabilityofPEMFCs.Theintegrationofadvancedmodelingandsimulationtools,suchasmultiscaleandmultiphysicsmodeling,canalsoenhanceourunderstandingofthecomplexanddynamicprocessesoccurringinPEMFCs,andfacilitatethedesignandoptimizationofthecathodeandothercomponents.Ultimately,thesuccessfulcommercializationofPEMFCsdependsonthebalanceofvariousfactors,suchasperformance,durability,cost,safety,andscalability,andthealignmentoftechnologicalinnovationwithsocialandenvironmentalneedsInadditiontoaddressingtechnicalchallenges,thewidespreaddeploymentofPEMFCsalsorequiresovercomingvariousnon-technicalbarriers.Onesuchbarrieristhelackofinfrastructureforproducing,storing,anddistributinghydrogenfuel,whichisnecessarytopowerPEMFCs.Currently,hydrogenismainlyproducedfromnaturalgas,butthereareeffortstodeveloprenewableandsustainablesourcesofhydrogen,suchaselectrolysisofwaterusingrenewableelectricityorbiomassgasification.However,thelowenergydensityandhighcostofhydrogenstorageanddistributionremainmajorchallengesthatneedtobeaddressed.

Anotherbarrieristheperceptionoffuelcellsasexoticandunfamiliartechnology,whichcancreateuncertaintyandriskforpotentialinvestorsandcustomers.Therefore,effortsareneededtoincreasepublicawarenessandunderstandingoffuelcellsandtheirbenefits,suchasreducedemissions,improvedenergysecurity,andeconomicdevelopment.Moreover,publicpoliciesandregulationscanplayacriticalroleincreatingasupportiveenvironmentforfuelcells,suchasbyprovidingincentivesandfundingforresearch,development,anddeployment,andbycreatingstandardsandcodesforsafetyandperformance.

Furthermore,thedeploymentofPEMFCsalsoraisesethicalandsocialissues,suchasthepotentialdisruptionofexistingenergysystemsandthedistributionofbenefitsandrisksamongdifferentstakeholders.Forexample,thetransitionfromfossilfuelstohydrogen-basedenergysystemscouldaffectthelivelihoodsofworkersandcommunitiesthatdependonthefossilfuelindustry.Therefore,ajustandequitabletransitionrequiresaddressingtheseissuesandengagingdiversestakeholders,suchasworkers,communities,andenvironmentalgroups.

Inconclusion,thedevelopmentanddeploymentofPEMFCsrequireamultidisciplinaryandintegratedapproachthataddressestechnical,environmental,social,andethicalaspects.WhilesignificantprogresshasbeenmadeinimprovingtheperformanceanddurabilityofPEMFCs,numerouschallengesremainthatrequirefurtherresearchanddevelopment.Moreover,thesuccessfulcommercializationofPEMFCsdependsoncreatingasu