光催化分解水制氢

光催化分解水制氢NanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscience2019年10月26日星期六IV-VIPbS0.4117PbSe？？PbTe0.3130II-VICdS2.425.4CdSe1.7010.0CdTe1.5610.2ZnTe2.410.4ZnSe2.829.2ZnS3.688.9ZnO3.359.0WO3TiO2CuO2eV=1240/λ光波波长对应的能量200nm6.2eV400nm3.1eV600nm2.067eV800nm1.55eVDopingatomsRu,Eu,2019年10月26日星期六氢的主要来源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NanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscienceNanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscience半导体光催化分解水热力学原理示意图+3.0+2.0+1.00.0-1.0BandgapH+H2H2OO2H+/H2O2/H2Oh+h+h+h+h+e-e-e-e-e-WaterreductionWateroxidationhvValencebandConductionbandH2O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）NanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscienceIntensityofsunlightversuswavelengthforAM1.5conditions.NanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscienceEnergybandpositionsforvarioussemiconductorsatpH14,thereductionandoxidationpotentialsofwatervarywith-59mVperpHunit.NanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscience纳米材料Si,GaAs,GaP,CdS,ZnO(unstable）AMWO6(A=Rb,Cs;M=Nb,Ta)SrTiO3,BaTi4O9K4Nb6O17,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。NanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscienceTiO2粒子中光生电子、空穴的衰减过程示意图+AA-体相复合表面复合hvhvEgTiO2粒子DABCD+-++----+++-导带价带---+++D+-+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,ClNanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscienceEnergydiagramofaPECcellforthephoto-electrolysisofwater.Thecellisbasedonann-typesemiconductingphoto-anode.NanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscienceNanjingUniversityofAeronauticsandAstronauticsInstituteofNanoscienceTiO2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·+100nsNano-sizedTiO2photocatalyst:opportunity&challengereporter：youshunLuansuperviser：Prof.hengyongXuDalianInstituteofChemicalPhysicsChineseAcademyofSciencesSeminarII4/2006Aim:Netsolar-to-hydrogenconversionefficiencyof10%MaincontentIntroductionAdvantage&shortageofTiO2※ModificationmethodsConclusion&outlook其6%2%17%75%其煤石油天然气其他中国10%24%40%26%石油煤天然气其他世界Situationofenergyresource&environmentSolarenergyisanabundant,economic,cleanreversibleresourcePhotocatalysis(UV-vis)isapromisingfieldforourenergysupply(H2O→H2)andcontrolofpollution(VOCoxidation)Mechanismofphotocatalysis++BB+--AA-hCBVBh+e-hv++Volumerecombination++surfacerecombinationWhyTiO2?1n-typeTiO2electrode2platinumblackcounterelectrode3ionicallyconductingseparator4gasburet5loadresistance6voltmeterFujishimaA.HondaK.,Nature，1972，37(1):238-245.•Goodphotoactivity(bandgap=3.2ev)oxidationofmostVOC&water•Photo&chemicalstability,non-toxicity•Lowcost,easeofavailabilityPhotocatalysisgoestoTiO2era!!ChallengeofTiO2!!!BecauseTiO2hasahighbandgap(~3.2eV),itisexcitedonlybyUVlight(λ388nm)toinjectelectronsintotheconductionband.Thus,thislimitstheuseofsunlight(3~5%)orvisiblelightasanirradiationsourceinphotocatalyticreactionsonTiO2.Inaddition,thehighrateofelectron–holerecombinationonTiO2particlesresultsinalowefficiencyofphotocatalysisModificationDecreasebandgapRestricte-/h+recombination•Transitionmetal•Noblemetal•Non-metal•Semi-conductorcombinationTi3dCBO2pUVVBNHEH+/H2O2/OH-CBVBh+e-UVMechanismofMn+dopingMn＋＝Cr3+,Co2+Fe3+…..Cr3dVisVis(nm)AV5+,Mn4+,Fe3+-dopedTiO2H.Yamashita,etalJ.PhotochemPhotobioA:Chem.148(2002)257–261Mo6+-dopedTiO2Y.Yang,etalJ.PhotochemPhotobioA:Chem.163(2004)517–522EfEEoEfVBCBsbmN-metaln-semiconductorSchottkyBarrierfromnoblemetal&n-semiconductor+--metalSchottkyBarrierhEffectivelyrestricte-/h+recombinationAg-TiO2H.M.Sung,etalJ.PhotochemPhotobioA:Chem.163(2004)37–44Ru-TiO2T.Ohno,etalJ.PhotochemPhotobioA:Chem.127(1999)107–110Ti3dVBCBO2pUVe-CBVBh+UVNHEH+/H2O2/OH-Xn-=N3-,C4-,S2-,P3-,F-…N2pVisVis(nm)AMechanismofXn-dopingF--dopedTiO2D.Li,etalJ.Fluor.Chem.126(2005)69–77N3--dopedTiO2D.Li,Mater.Sci.Eng.B117(2005)67–75CappedsemiconductorCoupledsemiconductore-e-h+h+TiO2CdSABB-(a)A+hhMechanismofsemiconductorcombinationh+TiO2CBVBe-e-h+h+A+ATiO2-WO3X.Z.Li,etalJ.PhotochemPhotobioA:Chem.141(2001)209–217TiO2-