光催化分解水制氢.ppt

光催化分解水制氢,NanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscience,2020年5月4日星期一,eV=1240/光波波长对应的能量200nm6.2eV400nm3.1eV600nm2.067eV800nm1.55eV,2020年5月4日星期一,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,H2OH2+1/2O2G0=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（0.30.4）,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（1.93.1eV）（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100psms(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+TiIVOH100nsshvb+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,IntroductionAdvantage&shortageofTiO2ModificationmethodsConclusion&outlook,其,其,石油,煤,天然气,其他,世界,Situationofenergyresource&environment,Solarenergyisanabundant,economic,cleanreversibleresourcePhotocatalysis(UV-vis)isapromisingfieldforourenergysupply(H2OH2)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(0.1Vincrementsforsingleelectrontransfersattheelectrodeelectrolyteinterface,DV=e/CCLU,whereeistheelectronicchargeandCCLUiscapacitance(aF),QuantizeddoublelayerchargingeffectsMurrayetal.Science,1998,280,2098andAnal.Chem.1999,71,3703,unitconductanceG0=2e2/h.,QuantizedconductancethroughindividualrowsofsuspendedgoldatomsH.Ohnishi,Y.Kondo&K.TakayanagiNature,395,780(1998),ChargeDistributioninTiO2-MetalSystemanditsroleinimprovingtheenergeticsofcompositecatalyst,EffectofGoldParticleSizeontheCatalyticReductionEfficiencyofTiO2particles,Vaidyanathan,Wolf,KamatJ.Am.Chem.Soc.,2004,126,4943-4950,E*f(TiO2)=Efb=-0.25+0.059log(C60eq/C60-)C60eq=C600C60,EffectGoldPerticleSizeontheFermiLeveloftheTiO2-AuCompositeCatalyst,Metal,VB,CB,e,e,e,Redoxcouple,hn,E*fApparentFermiLevelEfbFlatbandpotential,Subramanian,V.,etal.,CatalysiswithTiO2/AuNanocomposites.J.Am.Chem.Soc.,2004,126,4943-4950.,EstablishingthepropertyofelectronstorageinmetalParticles,Hirakawa,KamatLangmuir,2004,20,5645-5647,e,A-,Nelectrons,N-1electronsredshift,N+1electronsblueshift,Metalcluster,e,B+,Effectofexcesschargeontheelectronicproperties,KreibigetalMie-plasmonspectroscopy:Atoolofsurfacescience.inFineParticlesScienceandTechnology,Ed.E.Pelizzetti,NATO,p499,Chargetransferbetweenclusteratomsandthesurroundingspeciesalterstheelectrondensity,Theplasmonfrequencyofmetalclusterscanbeexpressedas,p=(Ne2/e0meff)Nistheconductionbandelectrondensity,meffistheeffectivemass,PhotoinducedchargeseparationandchargingofmetalcoreinAgTiO2,25nm,(A),ChargingandDischargingofElectronsintheMetalCore,Hirakawa,T.andKamat,P.V.,ElectronStorageandSurfacePlasmonModulationinAgTiO2Clusters.Langmuir,2004,20,5645-5647,Goldnanoparticles(2-8nmdiameter)improvethephotocatalyticperformanceofsemiconductornanoparticlesThesecompositesarepotentiallyusefulinthehydrogenproductionCactivityofotheroxide-metalandbimetalliccompositesneedtobeexplored,Semiconductor-MetalCompositeCatalystsforEnergyConversion,OpportunitiesexistforNanotechnologytopromoterevolutionaryandimportantbreakthroughsinenergytechnology.G