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1、SolarEnergyMaterials10(1984)287-302287North-Holland,AmsterdamPHOTOLYSISOFWATERWITHSUPPORTEDNOBLEMETALCLUSTERS,THEFATEOFOXYGENINTITANIABASEDWATERCLEAVAGESYSTEMSEdapoikayilYESODHARAN,SugunaYESODHARANandMichaelGRATZELInstitutdeChimiePhysique,EcolePolytechniqueFbdbrale,CH-1015Lausann
2、e,SwitzerlandReceived12January1984Controlledthermaldecompositionof(Rh)6(CO)l6clustersinthepresenceofTiO2(anatase)yieldshighlyactivecatalystswhichdecomposewaterunderilluminationbyasolarsimulatorwithanoveralllighttochemicalenergyconversionefficiencyof0.12~.Inthissystemescapeofoxyge
3、ninthegasphaseispreventedbyO2-photo-uptakeyieldingaperoxo-titaniumcomplex,probably/~-peroxotype,whichdissolvesin1MNaOHbutremainsontheTiO2particlesurfaceunderneutralconditions.Thecyclicfashioninwhichthesesystemsoperatesuggeststhattheperoxo-complexreleases02inareversiblefashionupon
4、flushingwithaninertgas.TheoxygencarrierfunctionoftheTiO2particlesisconfirmedbyquantitativetitrationwithpermanganateandexperimentscomparinghydrogen-oxygenrecombinationunderlightandinthedark.1.IntroductionInapreviouscommunication[1]wereportedonanewclassofwatercleavagecatalystsprepa
5、redviacontrolleddecompositionofnoblemetalclustercompoundssuchas(Rh)6(CO)t6andRu3(CO)12.Thismethod,developedrecentlybythegroupsofBasset[2],Brenner[3]andGates[4]servedustoproducehighlydispersednoblemetalsdepositedontotitaniumdioxide(anatase)particles.Excitationoftheseparticlesbysim
6、ulatedsunlightleadstoevolutionofhydrogenwithanoveralllighttochemicalconversionefficiencyapproachingthetheoreticallimitsexpectedforalargebandgapmaterialsuchasTiO2.Duringphotolysis,thereisnoorverylittleappearanceof02inthegasphase,aneffectwhichwasattributed[1]totheoxygencarrierprope
7、rtiesofTiO2.Thefateofphotogeneratedoxygenandthecyclicnatureofthehydrogengenerationprocess,characteristicforthesesystemsisfurtherinvestigatedinthepresentpaper.Theresultsconfirmourearlierpropositionconcerningtheformationofperoxo-titaniumcomplexesandruleoutTi3+ions,inadvertentlyform
8、edduringcatalystpreparation,asasacrifici