1、PhotoelectrochemicalWaterSplitting:Principles,ExperimentalMethods朱玉坤1.1ContentsPrinciplesAnalysisofbandgapandbandpositionsPhotoelectrochemicalexperimentalmethods1PrinciplesConductionbandBandgape+h+Ih+h+h+h+h+Valencebandy.vei+A:Absorptionofphotonstoformelectron-holepairsB:Chargeseparationandmigration

2、ofphotogeneratedcarriersC:ThesurfacechemicalreactionsD:SuppressionofrecombinationPrinciplesH2O-H2+O2AG=237kJ-mol1(E=AG/IF=1.23eV)Vacuum(eV)E(vsNHE)H+ConductionbandWaterreductionH+/H2(0V)H2o2Wateroxidation-2.5-2.0-3.0-1.5-3.5-1.0-4.0-0.5-4.50.05.06.07.0BandgapO2/H2O(123V)h+

3、h+h+h+h+Valenceband2.AnalysisofbandgapandbandpositionsA0.8h4molL1NaOH10molL1NaOHEg=1240Mrre一aoueqosqhv/eVndCMdC500600700800900300400Wavelength/nmrre-oueqosq3.1ElectrodePreparation32PhotoelectrochemicalCells33PhotoelectrochemicalMeasurements3.1ElectrodePreparationChemicalbathdeposition(CBD)Spraypyrol

4、ysisdeposition(SPD)Chemicalvapordeposition(CVD)So-calleddoctorbladeScreenprintingDipcoatingSpincoatingDirectgrowthonaconductingsubstrateNon-electrochemicalmethodsdsforelectrouepreparationhJElectrochemicalmethodsMethodbasedonpre-synthesizednanoparticlesElectrodepositionElectrochemicalanodizationElect

5、rophoreticanodization(b)3.1ElectrodePreparation(a)TheelectrodeswereaffixedwithAgpainttoapolyvinyIchloride-coatedcopperwirethathadbeenthreadedthrougha6-mmdiameterglasscapillary.Two-partepoxywasusedtocoverallsurfacesexceptthephotocatalystpowder-coatedsideoftheelectrode.)3.2PhotoelectrochemicalCellsvIE

6、RECP百、SelectingtheCounterElectrodeQuartzwindow.Lightpe2.5PhotoanodeUV:Visible:Infrared52$0*CBlackbodySpectrum1.5-RadiationatSeaLevel0.5-02505007501000125015001750200022502500Wavelength(nm)SelectingtheReferenceElectrodeREElectrolyteMediaAg/AgCIKCINeutralmediaHg/Hg2CI2(SCE)KCINeutralmediaHg/HgOKOHAlka

7、linemediaHg/Hg2SO4K2SO4AcidicmediaErhe二g/A旳+059XpH+0.197VSelectingtheElectrolyte3-3PhotoelectrochemicalMeasurementsBackilluminationfGlass/FTOc丿夕ElectrolyteFrontillumination,lightElectrolyteBiVO4BiJ.Phys.Chem.C,2011,115,17594-175983.3.1Photocurrent3.3.2Photopotential3.3.3Mott-Schottky3.3.4FlatBandPot

8、ential3.3.5ElectrochemicalImpedanceSpectra(EIS)3.3.6IncidentPhototoCurrentConversionEfficiency(IPCE)3.3.1PhotocurrentoJzdf0Jon7off)orphotocathode(/ph0Jon7off).Potentiodynamicconditions:thelightcanbecontinuouslyshinedontheelectrode,orchoppedwithadefinedon-offperiod.Animportantmagnitudethatcanbeobtain

9、edwithvoltammetryistheonsetpotential(EonsepV).Itisthepotentialvalueatwhichthephotocurrentacquiresanon-negligiblevalue.Potentiostaticconditions:theelectrodepotentialisfixed(keptconstant)duringthemeasurement.Thephotocurrentforinterruptedilluminationisrepresentedversustime(photocurrenttransient).3.3-2P

10、hotopotentialThephotopotential(Eph)canbedefinedasthedifferencebetweenthestationaryopen-circuitpotential(OCP)underillumination(Eph)andthatinthedark(Eo).Eph=lEphEqISimilarlytophotocurrentmeasurements,whentheOCPunderilluminationismorenegativethantheOCPinthedark(EphE0electronsarepreferentiallytransferre

11、dtosolution(photocathode)3-3.3Mott-SchottkyccapacitanceofthespacechargeregioninthesemiconductorNdelectroncarrierdensityEappliedpotentialeelementalchargeEjbflatbandpotentialopermittivityoffreespaceTtemperaturerelativepermittivityKBoltzmannconstant3.3.4FlatBandPotentialBandBendingF(ref)BuildinginVolta

12、ge(Vsc)Ecb0.02.0 x104.0 x10*6.0 x108.0 x103.3.5ElectrochemicalImpedanceSpectra6x10dark5x10-4x10-3x10-2x10-1x10-Z7QRtelectronmigrationresistanceinthethin-fllmphotoelectrodeRsolsolutionresistanceRsselectrontransferresistanceontheinterfaceCssinterfacecapacitanceWssWarburgresistancecausedbythediffusione

13、ffectoftheelectrolyte3.3.6IPCEIncidentPhototoCurrentConversionEfficiency(IPCE)1.63Vwebiasback-sidefront-side300350400450500550wavelength(nm)IPCE=1240X/”久XPlightoueqosqv0.0iiii300400500600700Wavelength(nm)300nmBiVO4o81o642oooUV-visdiffusereflectionspectraPotential/Vvs.Ag/AgCI7654321076543210020040060

14、0TimeIs80010002.00300600900120015001800Time/s04二縣uod1.0-0.5-0.0-0.4020.00.81.0Potential/Vvs.Ag/AgCIBFO2.0%BFO-RGO5.0%BFO-RGOACSJOURNALOFTHEAMERICANCHEMICALSOCIETYA/JACSFabricationofCaFe2O4/TaONHeterojunctionPhotoanodeforPhotoelectrochemicalWaterOxidation士十十十十EunSunKim/Naoy

15、ukiNishimura/GanesanMagesh；JaeYoungKim/Ji-WookJangHwichanJun；JunKubota/KazunariDomen；andJaeSungLee*,TDepartmentofChemicalEngineeringsDivisionofAdvancedNuclearEngineering,PohangUniversityofScienceandTechnology(POSTECH),77Cheongam-ro；Nam-gu;Pohang790-784；RepublicofKoreaDepartmentofChemicalSystemEngine

16、ering,TheUniversityofTokyo,7-3-1Hongo,BunkyoTokyo,JapanSchoolofNano-BioScienceandChemicalEngineering,UlsanNationalInstituteofScienceandTechnology(UNIST),50UNIST-gil,Ulsan,689-798RepublicofKoreaJAm.Chem.Soa,2013,135,5375-5383EXPERIMENTALSECTIONSynthesisofPhotocatalystPowder.Tantalumoxyn讓ridewassynthe

17、sizedbyheatingtantalumoxide(Kojundochemicals,99.9%)underNH弓gasflow(20mLmin1)at850Cfor15h.Calciumferritewassynthesizedbyaconventionalsolid-statereaction.AmixtureofCaCO(WakoPureChemicals99.99%)andFe2O3(WakoPureChemicals；999%)wasgroundinanagatemortarinthepresenceofethanolfor30minandcalcinedat1100Cfor5h

18、.FabricationofElectrodes.TheTaONelectrodewaspreparedbyelectrophoreticdepositiononF-dopedSnO2glass(FTO,AsahiGlass)inaconstantvoltagemodefollowingapreviouslyreportedprocedure.12TaONpowder(40mg)wasdispersedinacetone($0mL)withiodine(10m&Sigma-Aldrich?99.8%).Theaddition,ofiodinegaveH*bythereactionwithace

19、toneandthusmadeparticlespositivelycharged.TwoFTOglasseswereimmersedinthesolutioninparallelatadistanceof2cmand10Vofvoltagewasappliedbetweentheelectrodesfor2minusingadepowersupply.Thecoatedareawasabout1X1cm(denotedTaON-asdepositedelectrode).TheTaON-asdepositedelectrodewastreatedbyaTaCl5solutionforbett

20、erconnectionbetweenparticlesandelectrode.12The15“LofTaCl5solution(Aldrich99.8%,10mMinmethanol)wasdroppedontotheelectrodeanddried.Afterrepeatingthisprocessforfivetimes,theelectrodewasheattreatedinairat400Cfor30mintoobtainTaON-treatedelectrode.TheCaFe2O4layerwasdepos讓edontheTaON-treatedelectrodeaftert

21、heTaCl5solutiontreatment.TheCaFe2O4powderwasdispersedinacetonewiththesamecompositionasusedinTaONdeposition.Electrophoreticdepositionwasconductedbyapplying20Vbiasfor1min.ThetreatmentwithTaCl5solutionalsofollowed；andtheelectrodeswereheattreatedinairat400Cfor30mintoobtainTaON-treated/CaFe2O4electrode.I

22、naddition,CaFe2O4wasdepositeddirectlyontheTaON-asdepositedelectrode,omittingtheintermediateTaCl5solutiontreatmenttoobtainTaONasdeposited/CaFe2O4electrode.Thelastelectrodeensureddirectcontactbetween.TaONandCaFe2O4layers；andtheTaCl5treatmentwasconductedinthefinalsteponly.PhotoelectrochemicalMeasuremen

23、ts.ThePECcelltestwasconductedinathreeelectrodesystemwithapotentiostat(IviumstatfIviumTechnologies).Thefabricatedelectrode；aplatinummesh,andAg/AgCIelectrodewereusedasworkingscounterandreferenceelectrodesrespectively.Thecellwasmadeofquartzglass,and0.5MsodiumhydroxideatpH13.7wasusedasanelectrolyteafter

24、saturationwithnitrogengasfor30min.The300WXelamp(XeArclampsource,model66905丿Oriel)equippedwithaliquidIRfilter(Waterfilter,model61945,Oriel)andacutofffilter(A420nm;longpassfiltermodel59840,Oriel)wasusedtoirradiateonlyvisiblelight.Thephotocurrentwasmeasuredbylinearsweepvoltammetryfrom1.2to0.8VvsAg/AgCI

25、)withascanrateof0.01V/s.ThelightirradiationcamefromthebacksideofFTOglassforallcases.Formeasurementsofincidentphotontocurrentefficiency(IPCE)?the300WXelampwasusedwithaliquidIRfilterandamonochromator(OrielCornerstone1301/8mmonochromator)withabandwidthof5nm.Thecutofffilter(299nm)wasplacedattheexittopre

26、ventX/2radiationoriginatedbyBraggdiffractionatthegrating.Theincidentlightintensitywasmeasuredusingaradiantpowermeter(model70260；Oriel)withaphotodiodedetector(model70282,Oriel).Potentiostaticelectrochemicalimpedancespectroscopy(EIS)wascarriedoutatadepotentialof0.2VvsAg/AgCIwithanacpotentialfrequencyr

27、angefrom100000to0.1Hz.TheprogramZView(ScribnerAssociatesInc)wasusedtofittheobtaineddatatothecorrespondingequivalentcircuitmodel.Co-catalystLoadingandGasEvolutionMeasurements.Anoxygenevolvingco-catalyst；cobaltphosphate(Co-Pi)7waselectrodepos讓edinathreeelectrodesystembythemethodreportedelsewhere?1Thef

28、abricatedelectrode?aplatinummesh,andAg/AgClwereusedasworking,counter,andreferenceelectrodes,respectively.Theelectrolytesolutionwas0.5mMcobaltnitratehexahydratein0.1MpH7potassiumphosphate(KPi)buffer.Theelectrodepositionwasconductedbyapplying1.0VvsAg/AgClfor2min.Afterdepositionoftheco-catalyst,theelec

29、trodeswerewashedwithdistilledwaterandusedtomeasurephotocurrent.Theelectrolyteforphotoelectrochem-icalcellwas0.1MKPibufferedatpH11.5with0.1MKOH.Thehydrogenandoxygenevolutionbyphotoelectrochemicalwatersplittingwasconductedintheairtightreactorconnectedtoaclosedgascirculationsystem.TheS00WHglamp(HgArcla

30、mpsource,model66902,Oriel)equippedwithaliquidIRfilter(Waterfilter,model61945,Oriel)andacutofffilter(2400nm,longpassfiltermodel59472，Oriel)wasusedtoirradiateonlyvisiblelight.TheamountofhydrogenoroxygenwasdeterminedbyagaschromatographyequippedwithTCD(HP6890,molecularsieve5Acolumn,Arcarriergas).Lightso

31、urcesLightsourceofUVHighpressureHglampLightsourceofVIS300WXelamp+filterSolarsimulator(AM-1.5)、Hglamp:VacuumpumpPressuregaugeArcarriergas1VacuumpumpGas-circulationpumpReactioncellforUVirradiation(innerirradiationtype)FilterReactioncellforVISirradiationXelampLiebigcondenserChem.SoaRev.,2009,38,253-278

32、10203040506070802o(degree)(nsAlrsusu一765432(W.M)3ouqJ0sq420nm).Schematamodelsforfourelectrodesareakoshown.(a)iooo800W600-TaQN-adeposited二400TaOM-trcato-dMT3ON-tre3tedCaFe2O4.TaQN/CaFQnO4.2000-護(hù)ry02004006008001000r(ohm)(b)|CaFe2O4D347nf朋300350400450500550600650700TaONVD.482nm3530252015105(*)山02me.aoueqJQSqvR420nm)atadepotentialof0.2VvsAg/AgClwithxnacpotentiarfrcquencj-rangefromlOOOOOto0.1Hl(b)EquivilentdreuitanodeLHolereactionsonthesurfaceandelectronflowthroughthes