光催化分解水制氢ppt课件.ppt

光催化分解水制氢 NanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscience 2019年12月22日星期日 eV 1240 光波波长对应的能量200nm6 2eV400nm3 1eV600nm2 067eV800nm1 55eV 2019年12月22日星期日 氢的主要来源 电解水制氢 商业化电解水的效率 85 热化学法分解水制氢石油产品催化重整制氢生物质原料催化重整制氢生物制氢硫化氢裂解制氢光催化分解水制氢 NanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscience 纳米粒子光催化分解水的要求 强吸收太阳光 主要可见光 化学性质稳定合适的能带适合水的氧化还原在半导体中电荷能有效转移氧化还原反应时具有低的超电势低成本 高效率 NanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscience NanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscience 半导体光催化分解水热力学原理示意图 3 0 2 0 1 0 0 0 1 0 Bandgap H H2 H2O O2 H H2 O2 H2O h h h h h e e e e e Waterreduction Wateroxidation hv Valenceband Conductionband H2O H2 1 2O2 G0 238kJ mol E Go nF 1 23eV V NHE 最佳能隙范围 半导体纳米粒子的能隙大于热力学分解电压 1 23eV 热动力学损失 0 4eV 超电势 0 3 0 4 约1 9eV 对应的波长约为650nm 在400nm 3 1eV 以下太阳光强度急剧下降 半导体纳米粒子的最佳能隙范围 1 9 3 1eV 400 650nm NanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscience IntensityofsunlightversuswavelengthforAM1 5conditions NanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscience EnergybandpositionsforvarioussemiconductorsatpH14 thereductionandoxidationpotentialsofwatervarywith 59mVperpHunit NanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscience 纳米材料 Si GaAs GaP CdS ZnO unstable AMWO6 A Rb Cs M Nb Ta SrTiO3 BaTi4O9K4Nb6O17 K2La2Ti3O10 MTaO3 ZrO2 Ta2O5 TiO2 3 2eV SnO2 3 6eV Fe2O3 2 1 2 2eV CdS CdSe WO3 Cu2O NanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscience 主要的优化方法 掺杂 调控能带 C N 过渡金属或稀土掺杂等 包覆 降低超电势 增加稳定性 提高电子空穴分离效率 提供析氢活性中心 贵金属等 染料分子或者稀土配合物敏化 NanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscience 加大电子和空穴的迁移率 金属氧化物的导带和价带分别和金属的3d轨道 O的2p轨道相关 金属的3d轨道重叠越多 电子的迁移率越高 O2p轨道的重叠程度影响空穴的迁移率 尽量减少半导体纳米粒子的缺陷 减少电子 空穴对的再结合位点 NanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscience TiO2粒子中光生电子 空穴的衰减过程示意图 TiO2纳米粒子催化性能改进方法 制备更细的纳米粒子 提高比表面积 减少空穴迁移到表面的距离 减少电子空穴对再结合的机会 掺杂过渡金属阳离子 Fe Cr 掺杂C N S P F Cl NanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscience EnergydiagramofaPECcellforthephoto electrolysisofwater Thecellisbasedonann typesemiconductingphoto anode NanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscience NanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscience TiO2中光生电子 空穴的不同衰减过程的特征弛豫时间 电子 空穴的产生 TiO2 hvhvb ecb fs载流子被捕获过程 hvb TiIVOHTiIVOH 10nsecb TiIVOHTiIIIOH轻度捕获100ps ms 动力学平衡 ecb TiIVTiIII深度捕获10ns 不可逆 电子 空穴的复合 ecb h hvorpsecb TiIVOH TiIVOH100ns shvb TiIIIOHTiIVOH10ns表面电荷转移 etr OxTiIVOH Ox 很慢ms 主要过程特征时间尺度 TiIVOH RedTiIVOH Red 100ns Nano sizedTiO2photocatalyst opportunity challenge reporter youshunLuansuperviser Prof hengyongXu DalianInstituteofChemicalPhysicsChineseAcademyofSciences SeminarII 4 2006 Aim Netsolar to hydrogenconversionefficiencyof10 Maincontent Introduction Advantage shortageofTiO2 Modificationmethods Conclusion outlook 其 其 石油 煤 天然气 其他 世界 Situationofenergyresource environment Solarenergyisanabundant economic cleanreversibleresourcePhotocatalysis UV vis isapromisingfieldforourenergysupply H2O H2 andcontrolofpollution VOCoxidation Mechanismofphotocatalysis WhyTiO2 1n typeTiO2electrode2platinumblackcounterelectrode3ionicallyconductingseparator4gasburet5loadresistance6voltmeter FujishimaA HondaK Nature 1972 37 1 238 245 Goodphotoactivity bandgap 3 2ev oxidationofmostVOC waterPhoto chemicalstability non toxicityLowcost easeofavailabilityPhotocatalysisgoestoTiO2era ChallengeofTiO2 BecauseTiO2hasahighbandgap 3 2eV itisexcitedonlybyUVlight 388nm toinjectelectronsintotheconductionband Thus thislimitstheuseofsunlight 3 5 orvisiblelightasanirradiationsourceinphotocatalyticreactionsonTiO2 Inaddition thehighrateofelectron holerecombinationonTiO2particlesresultsinalowefficiencyofphotocatalysis ModificationDecreasebandgapRestricte h recombinationTransitionmetalNoblemetalNon metalSemi conductorcombination Ti3d CB O2p UV VB NHE H H2 O2 OH CB VB h e UV MechanismofMn doping Mn Cr3 Co2 Fe3 V5 Mn4 Fe3 dopedTiO2 H Yamashita etalJ PhotochemPhotobioA Chem 148 2002 257 261 Mo6 dopedTiO2 Y Yang etalJ PhotochemPhotobioA Chem 163 2004 517 522 Ef E Eo Ef VB CB s b m N metal n semiconductor SchottkyBarrierfromnoblemetal n semiconductor metal SchottkyBarrier h Effectivelyrestricte h recombination Ag TiO2 H M Sung etalJ PhotochemPhotobioA Chem 163 2004 37 44 Ru TiO2 T Ohno etalJ PhotochemPhotobioA Chem 127 1999 107 110 Ti3d VB CB O2p UV e CB VB h UV NHE H H2 O2 OH Xn N3 C4 S2 P3 F N2p Vis Vis MechanismofXn doping F dopedTiO2 D Li etalJ Fluor Chem 126 2005 69 77 N3 dopedTiO2 D Li Mater Sci Eng B117 2005 67 75 Cappedsemiconductor Coupledsemiconductor Mechanismofsemiconductorcombination TiO2 WO3 X Z Li etalJ PhotochemPhotobioA Chem 141 2001 209 217 TiO2 CdS Y Bessekhouad etalJ PhotochemPhotobioA Chem 163 2004 569 580 Othermodificationmethods Surfacephoto sensitizationSurfaceoxidation reductionSurfacehyper acidificationSurfacechelatingElectric assistedphotocatalysis Conclusion Outlook TiO2hasbeenwidelyused owingtoitsuniquephysicalandchemicalproperty asagoodphotocatalysttoremoveorganiccontaminantandsupplyhydrogenfromwaterDespitesomeinherentlimitationsofTiO2 wehavesucceededinmodifyingitspropertyandimprovingitsquantumefficiencyandapplicationareaToutilizesolarenergymoreeffectively fartherimprovementofTiO2modificationdevelopnewmaterialsforphotocatalysis InVO4 understandingofphotocatalysiskinetics mechanismonelectronleveldeactivation regenerationofphotocatalyst Reference FujishimaA HondaK Nature 1972 37 1 238 245 CornishBJPA etal J 1AppliedCatalysisB Environ 2000 25 59 67YuJiaGuo CJimmy etal J J SolidStateChem 2003 174 372 377IharaT etal J Appl Catal B Environ 2003 42 403 409H Yamashita etalJ PhotochemPhotobioA Chem 148 2002 257 261Y Yang etalJ PhotochemPhotobioA Chem 163 2004 517 522H M Sung etalJ PhotochemPhotobioA Chem 163 2004 37 44T Ohno etalJ PhotochemPhotobioA Chem 127 1999 107 110D Li etalJ Fluor Chem 126 2005 69 77D Li Mater Sci Eng B117 2005 67 75X Z Li etalJ PhotochemPhotobioA Chem 141 2001 209 217Y Bessekhouad etalJ PhotochemPhotobioA Chem 163 2004 569 580 ApplicationofZirconiumDioxideasaNewPhotocatalyst ByChristopherCiptadjayaCHEM6100 Overview Photocatalyst Advantages Applications PropertiesofZirconiumDioxideComparisonofZirconiumDioxideandTitaniumDioxideBandGapEnergyANewPhotocatalyst ZirconiumDioxidePhotoreductionofCO2 selectedpaper Summary Photocatalyst AcatalystthatacceleratesphotoreactionDoesnotchangeinitselforbeingconsumedinthechemicalreactionSinceitspropertywasdiscoveredin1968 titaniumdioxide TiO2 hasbeentheprimaryphotocatalystusedinvariousapplicationsinindustryIthasstrongoxidationanddecompositionstrengthPhotocatalyticactivity PCA istheabilityofamaterialtocreateanelectronholepairasaresultofexposuretoultravioletradiation PhotosynthesisandPhotocatalysis HowDoesPhotocatalystWork AdvantagesofUsingPhotocatalyst DegradationofpollutantsatambientairandtemperatureAdaptedforalargerangeofpollutantBuildwitheasilyavailablematerialsandbymeanofwell knowntechniquesEconomical cheapandlowenergyconsumptionExcellenttransparentandstrength possibleforcoating ApplicationofPhotocatalyst Photocatalyticsuperhydrophilicitytechnology e g anti foggingandself cleaningpropertiesOilonthesuper hydrophilicsurfaceiseasilyremovedbysoakingthematerialinwaterHydroxylradicalskillsbacteriaandbreaksdownodor causingorganiccompounds PropertiesofZrO2 StablechemicalpropertiesLowthermalconductivityLargebandgapsemiconductorpropertiesCanberecoveredeasilyAmpothericpropertyHighactivityforheterogeneousphotochemicalprocessHighadsorptiontowiderangeofpollutants EnergyBandGapofMaterials ZrO2 widebandgapsemiconductororlowendinsulator Eg 5 0eV BandGapandChargeDistributionofZrO2vsTiO2 VB e h h 3 2eV CB ZrO2 Vs 5 0eV VB CB e h h TiO2 e e e e FermiLevel 250nm 378nm ElectronTrappingandStorageinZrO2ConductionBand hn 5 0eV VB CB e h h e e VB CB e h h e e 5 0eV FermiLevel EF e e e e ANewPhotocatalystApplicationofZirconiumDioxide Watersplitting H2fuel Photooxidationoforganicmolecules eg AnilinetoazobenzeneDegradationof2 4 dichlorophenoxiaceticacidand2 4 6 trichlorophenolPhotocatalyticDegradationofTrichloroethylenePhotoreductionofCO2 PhotocatalyticWaterSplitting Hydrogenisanimportantchemicalfeedandnon pollutingrenewablefuelZrO2photocatalyzesthedecompositionofwaterintoH2andO2ZrO2preparedbyprecipitationmethodofzirconiumoxychloridewithvarioushydrolyzingagentswasstudiedforphotocatalyticwatersplittingreactionunderUVirradiation KoreanJ Chem Eng 2003 20 1026 Reykjavik Iceland Paperofinterest ANewTypeOfPhotocatalysisInitiatedByPhotoexcitationOfAdsorbedCO2OnZrO2SatohiroYoshidaandYoshiumiKohno CatalysisSurvey 2000 4 107 CarbonDioxide CO2 AverystableandinertcompoundBiomassrespirationGeneratedfromelectricity steamPotentgreenhousegasCausesglobalwarming www rst gsfc nasa gov WhyWorriedAboutExcessiveCO2Emission Trapre radiatedenergyCausesgreenhouseeffectAffectsclimatechangeElevatedtemperature SynthesisandPhotochemistryofZirconiumDioxide HydrolysiszirconiumoxychloridebyNH3Dryat373KovernightCalcinateat773Kfor5hoursinadryairsteamPhotoreactionwasdoneusing500WMercurylampasUVlightsourceMixtureofCO2withH2orCH4wasinjectedtothesystem TimeDependencePlotofAmountofCOFormationandH2Consumption EffectofReactionTemperatureonPhotoreactionofCO2 H2 SurfaceIntermediates IntroductionofCO2causestheappearanceof6bandscorrespondingtosurfacecarbonatesandbicarbonatesSecondsurfacespecieswasformedduringphotoirradiationofZrO2bythereactionbetweenhydrogenandadsorbedcarbondioxideThesespeciesaresurfaceformateion WhatistheRoleofSurfaceFormate Involvesinreactionpathwayorspectator Investigation FormicacidwasusedassubstrateObservationofevolutionofCOusingformicacidasareactant13CO2wasusedandtheevolutionofCOwasobservedFormateactsasareductantofCO2 FormationofCO2 Radicals CO2isadsorbedascarbonatesonthesurfacePhotoexcitationofmoleculescausesactivationofCO2ActivatedspeciesareradicalsRecordedwithEPR ElectroParamagneticResonance ResultsfromEPRspectrasuggestCO2 radicalsformedPrecursorofCO2 radicalsformationiscarbonateformationonthesurface SummaryofReactionMechanismforPhotoreductionofCO2byH2overIrradiatiedZrO2 CO2 radicalsisformedbyphotoactivationofadsorbedCO2CO2 radicalsreactswithH2toformsurfaceformateSurfaceformateworksasareductantofCO2toCOunderirradiationSurfaceformateisbeingreoxidizedtobecomeadsorbedCO2speciesagain SummaryofreactionmechanismforphotoreductionofCO2bymethaneoverirradiatedZrO2 CO2 radicalsreactswithCH4producingsurfaceacetateandsurfaceformateSurfaceacetatedoesnotreactSurfaceformateworksasareductantofCO2toCOunderirradiationSurfaceformateisbeingreoxidizedtobecomeadsorbedCO2speciesagain Conclusion ZrO2isanactivephotocatalystforphotoreductionofCO2byhydrogenandmethaneRoleofphotoirradiationareasfollows ToconvertadsorbedcarbonatestoCO2 radicalsToassistreactionofCO2andformatederivedfromCO2 andhydrogenormethaneZrO2photocatalystpromisesanalternativesolutionforthereductionofCO2emission Semi conductormaterialsaredopedwithimpuritieschosentogivethematerialspecialcharacteristics OnemaywanttoaddextraelectronsorremoveelectronsN typesemiconductor currentiscarriedbya electronP typesemiconductor currentiscarriedbya hole PhotocatalyticWaterSplitting FactorswhichhavebeenconsideredinPhotocatalysisofWaterSplitting BandgapandbandpositionBandBendingCocatalysts JunctionstructureSurfaceareaDefectsincrystalstructureandcompositionSolutionpH ExternaladditiveStabilityagainstphotocorrosion PHOTOCATALYSIS CHALLENGESANDPOTENTIALS Prof B ViswanathanDepartmentofchemistryIndianInstituteofTechnology Madras PhotocatalysisConventionalredoxreactionOxidizingagentshouldhavemorepositivepotentialPhotocatalysis simultaneousoxidationandreductionTheredoxcouplecapableofpromotingboththereactionscanactasphotocatalystMetals SemiconductorsandInsulators reactionassistedbyphotons catalyst 70 MetalsNobandgapOnlyreductionoroxidationDependsonthebandpositionInsulatorsHighbandgapHighenergyrequirement WHYSEMICONDUCTOR 71 Forconventionalredoxreactions oneisinterestedineitherreductionoroxidationofasubstrate ForexampleconsiderthatonewereinterestedintheoxidationofFe2 ionstoFe3 ionsthentheoxidizingagentthatcancarryoutthisoxidationischosenfromtherelativepotentialsoftheoxidizingagentwithrespecttotheredoxpotentialofFe2 Fe3 redoxcouple TheoxidizingagentchosenshouldhavemorepositivepotentialwithrespecttoFe3 Fe2 couplesoastoaffecttheoxidation whiletheoxidizingagentundergoesreductionspontaneously Thissituationthrowsopenanumberofpossibleoxidizingagentsfromwhichoneofthemcanbeeasilychosen Concepts Whysemiconductorsarechosenasphoto catalysts 72 Watersplitting carryoutboththeredoxreactionssimultaneously reductionofhydrogenions 2H 2e H2 aswellas 2OH 2h H2O 1 2O2 oxygenevolutionfromthehydroxylions Thesystemthatcanpromoteboththesereactionssimultaneouslyisessential Sinceinthecaseofmetalsthetopofthevalenceband measureoftheoxidizingpower andbottomoftheconductionband measureofthereducingpower arealmostidenticaltheycannotbeexpectedtopromoteapairredoxreactionsseparatedbyapotentialofnearly1 23V wherethetopofthevalencebandandbottomoftheconductionbandareseparatedatleastby1 23Vinadditiontotheconditionthatthepotentialcorrespondingtothebottomoftheconductionbandhastobemorenegativewithrespecttobemorenegativewithrespecttowhilethepotentialofthetopofthevalencebandhastobemorepositivetotheoxidationpotentialofthereaction2OH 2h H2O O2 73 Thissituationisobtainablewithsemiconductorsaswellasininsulators Insulatorsarenotappropriateduetothehighvalueofthebandgapwhichdemandshighenergyphotonstocreatetheappropriateexcitonsforpromotingboththereactions Theavailablephotonsourcesforthisenergygapareexpensiveandagainrequireenergyintensivemethods Henceinsulatorscannotbeemployedforthepurposeofwatersplittingreaction Therefore itisclearthatsemiconductorsarealonesuitablematerialsforthepromotionofwatersplittingreaction 74 Criteriononehastousefortheselectionofthesemiconductormaterialsandalsohowonecanfinetunethematerialthuschosenforthewatersplittingreaction Essentiallyforphoto catalyticsplittingofwater thebandedges thetopofvalencebandandbottomoftheconductionbandortheoxidizingpowerandreducingpowerrespectively havetobesiftedinoppositedirectionssothatthereductionreactionandtheoxidationreactionsarefacile 75 IonicsolidsastheionicityoftheM Obondincreases thetopofthevalenceband mainlycontributedbythep orbitalsofoxideions becomeslessandlesspositive sincethebindingenergyoftheporbitalswillbedecreasedduetonegativechargeontheoxideions andthebottomoftheconductionbandwillbestabilizedtohigherbindingenergyvaluesduetothepositivechargeonthemetalionswhichisnotfavourableforthehydrogenreductionreaction MoreionictheM Obondofthesemiconductoris thelesssuitablethematerialisforthephoto catalyticsplittingofwater ThebondpolaritycanbeestimatedfromtheexpressionPercentageioniccharacter 76 ThepercentageioniccharacteroftheM Obondforsomeofthesemiconductors 77 Theoxidesemiconductorsthough suitableforthephoto catalyticwatersplittingreactionintermsofthebandgapvaluewhichisgreaterthanthewaterdecompositionpotentialof1 23V Mostofthesesemiconductorshavebondcharactermorethan50 60 andhencemodulatingthemwillonlyleadtoincreasedioniccharacterandhencethephoto catalyticefficiencyofthesystemmaynotbeincreasedasperthepostulatesdevelopedThereforefromthemodeldevelopedinthispresentationthefollowingpostulateshavebeenevolved 78 Thephoto catalyticsemiconductorsareoftenusedwithadditionofmetalsorwithotherholetrappingagentssothatthelifetimeoftheexcitonscreatedcanbeincreased Thissituationistoincreasethelifetimeoftheexcitedelectronandholesatsuitabletrapssothattherecombinationiseffectivelyreduced Inthismode thepositionsoftheenergybandsofthesemiconductorandthatofthemetaloverlapappropriatelyandhencethealterationcanbeeitherwayandalsointhissenseonlytheelectronsaretrappedatthemetalsitesandonlyreductionreactionisenhanced 79 Henceweneedstoichiometricallybothoxidationandreductionforthewatersplittingandthisreactionwillnotbeachievedbyoneofthetrappingagentsnamelythatisusedforelectronsorholes Evenifoneweretousethetrappingagentsforbothholesandelectrons therelativepositionsoftheedgeofthevalencebandandbottomoftheconductingbandmaynotbeadjustedinsuchawaytopromoteboththereactionssimultaneously 80 Normallythesemiconductorsusedinphoto catalyticprocessesaresubstitutedinthecationicpositionssoastoalterthebandgapvalue Eventhoughitmaybesuitableforusingtheavailablesolarradiationinthelowenergyregion itisnotpossibletousesemiconductorswhosebandgapislessthan1 23Vandanythinghigherthanthismaybefavourableifboththevalencebandisdepressedandtheconductionbandisdestabilizedwithrespecttotheunsubstitutedsystem Sincethissituationisnotobtainableinmanyoftheavailablesemiconductorsbysubstitutionatthecationicpositions thismethodhasnotalsobeensuccessful 81 Inadditionthedissolutionpotentialofthesubstitutedsystemsmaybemorefavourbalethanthewateroxidationreactionandhencethiswillbethepreferredpathway Thesesubstitutedsystemsoreventhebaresemiconductorswhichfavourthedissolutionreactionwillundergoonlypreferentialphoto corrosionandhencecannotbeexploitedforphoto catalyticpathway InthiscaseZnOisatypicalexample 82 Verylowvalueoftheioniccharacteralsoisnotsuitablesincethesesemiconductorsdonothavethenecessarybandgapvalueof1 23V thesearchforutilizinglowerendofthevisibleregionisnotpossiblefordirectwatersplittingreaction Ifoneweretousevisibleregionofthespectrum thenonlyoneofthephoto redoxreactionsinwatersplittingmaybepreferentiallypromotedandprobablythisaccountsforthefrequentobservationthatnon stiochiometricamountsofoxygenandhydrogenwereevolvedinthephoto assistedsplittingofwater 83 Thereforeitisdeducedthatthesystemswhichhasionicbondcharacterofabout20 30 withsuitablepositionsofthevalenceandconductionbandedgesmaybeappropriateforthewatersplittingreaction Thisrationalizationhasgivenoneahandletoselecttheappropriatesystemsforexaminingasphoto catalystsforwatersplittingreaction 84 Therearesomeotheraspectsofphoto catalystsonwhichsomeremarksmaybeappropriate Thoughtheyhavebeenderivedfromthesolidstatepointofviewlikeflatbandpotential bandbending Fermilevelpinning theseparametersalsocanbeunderstoodintermsofthebondcharacterandtheredoxchemicalaspectsbywhichthewatersplittingreactionisdealt 85 PROCESSESONTHEPHOTO EXC