Chloride Oxidation as an Alternative to the Oxygen-Evolution Reaction on H - Breuhaus-alvarez et al. - 2021 - Unknown

《Chloride Oxidation as an Alternative to the Oxygen-Evolution Reaction on H - Breuhaus-alvarez et al. - 2021 - Unknown》由會(huì)員上傳分享，免費(fèi)在線閱讀，更多相關(guān)內(nèi)容在學(xué)術(shù)論文-天天文庫。

pubs.acs.org/JPCCArticleChlorideOxidationasanAlternativetotheOxygen-EvolutionReactiononHxWO3PhotoelectrodesAndrewG.Breuhaus-Alvarez,QuintinCheek,JoshuaJ.Cooper,StephenMaldonado,andBartM.Bartlett*CiteThis:J.Phys.Chem.C2021,125,8543?8550ReadOnlineACCESSMetrics&MoreArticleRecommendations*s?SupportingInformationABSTRACT:Acomparisonofphotoelectrochemicaloxygen-evolutionreaction(OER)andchlorideoxidationisperformedonsemiconductingHxWO3thin?lms.Overa3hcontrolledpotentialcoulometry(CPC)experiment,thephotocurrentdensityrecordedduringOERinanitrateelectrolytedecreasestohalfthestartingphotocurrent.However,ifthesameelectrolysisexperimentisperformedwithachlorideelectrolyte,thephotocurrentdensityismuchmorestable,degradingbyonly5%overthesameperiod.Linearsweepvoltammetry(LSV)inthenitrateelectrolyteexhibitsafootofthewaveapproximately150mVmorepositivethaninthechlorideelectrolyteandthesaturatedphotocurrentdensityisapproximately20%greaterinthechlorideelectrolytecomparedtothenitrateelectrolyte.Also,theFaradaice?ciency(FE)fortheOERis87±2%inthenitrateelectrolytecomparedtoanFEof100%fortheoxidationofthechlorideelectrolytetohypochlorousacid.TheseresultssuggestthatthechlorideionrapidlyinjectselectronsintothephotogeneratedholesintheHWOvalencebeforetheseholesdestructivelyrecombinewithW5+electrondonors.x3TheresultisanincreaseinHxWO3stabilityduringphotoelectrochemicalchlorideoxidationwhencomparedtowateroxidation.FeOOHelectrocatalystsareknowntoe?cientlyremoveholesfromphotoresponsivemetaloxides,andFeOOHwasdepositedonHxWO3.TheHxWO3|FeOOHmaterialalsoexhibitsanegligiblelossofphotocurrentduringOERandchlorideoxidation,supportingthishypothesis.■INTRODUCTIONdiformylfuranortheformationofvariousoxidizingagents4?6likepersulfateandsodiumhypochlorite.ProducingsolarfuelshaslargelyfocusedonprotonreductionDownloadedviaBUTLERUNIVonMay16,2021at08:08:09(UTC).ChlorideanionoxidationisanattractivealternativeduetoatthecathodetoformH2andtheoxygen-evolutionreactionthelargeamountofbrinewateronEarthandthefastkinetics(OER)attheanodeaccordingtothereactionsofthetwo-electronoxidationofchloridetochlorineor+?hypochlorite.7?92H(aq)2e+→H(g),2NE°=0VHE(1)Seehttps://pubs.acs.org/sharingguidelinesforoptionsonhowtolegitimatelysharepublishedarticles.2Cl(aq)??→+°Cl(g)2e,E=1.36V+?2NHE(3)2HO(l)22→+4H(aq)4e+°O(g),E=1.23VNHE(2)?Cl(aq)+HO(l)2However,whilethewateroxidationproducesnogreenhouse?+?gasses,thecommercialvalueoftheOproductislow,the→++ClO(aq)2H(aq)2e,E°=1.72VNHE(4)2thermodynamicpotentialforwateroxidationishigh(1.23VvsChlorideoxidationisindustriallyperformedbytheNHE),andthereactionisslowduetomultiproton,chloralkaliprocesstoproduceCl2gasandNaOH,bothofmultielectronnatureofthereaction.Furthermore,carryingwhicharerequiredforover50%ofindustrialchemicalouttheOERondi?erentelectrochemicalandphoto-processes.10,11Apartfromstronglyacidicaqueoussolutions,electrochemicalplatformstypicallyexhibitssigni?cantdegra-dation,whichlimitsthelong-termviabilityofOERforsolarfuelproduction.DegradationmechanismsincludechangesinReceived:December18,2020oxidationstate,dissolution,andmigrationoftheactiveRevised:March10,2021material.1?3AlternativestotheOERarethenimportant,Published:April14,2021particularlythosethatproducevaluableoxidationproductsatstablecurrentdensities.Examplesincludetheoxidationoforganiccompoundslike5-hydroxymethylfurfuralto2,5-?2021AmericanChemicalSocietyhttps://doi.org/10.1021/acs.jpcc.0c112828543J.Phys.Chem.C2021,125,8543?8550

1TheJournalofPhysicalChemistryCpubs.acs.org/JPCCArticleCl2reactsinaqueousenvironmentstoproducehypochlorite?owingN2stream.Ag/AgClreferenceelectrodeswereanioninbasicsolutionsorhypochlorousacidinmoreacidicpurchasedfromCHInstrumentsand?lledwithsaturated12conditions(pKa=7.4).Also,recentworkinourgrouphasKClaqueoussolution.99.95%purePtwire(24gauge,P/NshownthattheOERonHxWO3proceedsbytheformationof1981)waspurchasedfromSurePureChemetals.13,14hydroxylradicalspecies.SynthesisofHxWO3Electrodes.HxWO3electrodeswere?+?synthesizedbyspincoatingusingaprocedurepreviouslyHO(l)2N→++OH(aq)H(aq)e,E°=2.7VHEreported.2Thespincoatsolutionwasmadebyadding2.51g(5)(833μmol)ofAMTtoa100mLround-bottom?askandthen14Chlorideoxidationmayproceedthrougharadicalaswell.adding10mLofwatertodissolvecompletelywithvigorous???stirring.Separately,6.6g(22mmol)ofPEG-300wasdissolvedCl(aq)→+Cl(aq)e,E°=2.6VNHE(6)in10mLofethanolinascintillationvial.TheethanolsolutionHowever,thehydroxylradicalreductionpotentialisatawasslowlyaddedtotheaqueoussolutionbyapipettewhilemorepositivepotentialthanthechlorideradicalreductionstirringvigorouslyoverthecourseofapproximately3min,potential.Therefore,chlorideoxidationisexpectedtobetheresultinginafaint,o?-whitesolprecursor,whichwas0.5MinthermodynamicallyfavoredreactiononHxWO3regardlessoftungsten.ElectrodesforPECmeasurementswerepreparedbyformationofachlorideradicalisrequiredinthechloridedropping200μLoftheprecursorsolontoclean,2.54cmsquares(6.45cm2)ofFTOandthenspunat2500rpmfor30soxidationmechanism.Inthismanuscript,wedemonstratetheoxidationofchlorideusingaLaurelspincoater.Afterspincoatingalayer,the?lmbytungstenoxidegeneratedbyprocessinganammoniumwasplacedintoa500°Cmu?efurnacefor30min.Thespinmetatungstatesol,whosechemistryisbestdescribedasthecoatandannealprocedurewasrepeatedforatotalof10times2formulaHxWO3inpH4solutions.Thevalencebandoftomakethe1μmthick?lmsusedinthiswork.TheHxWO3HxWO3(3VvsNHE)issu?cientlypositivetoprovidetheelectrodesusedinthedetectionofoxidizedchlorideproductsbythestarch-iodidetestwere1.5cmsquares(2.25cm2)andoverpotentialrequiredfortheoxidativereactionspresentedin15?18eqs2?6.Chlorideoxidationisalsokineticallysimpler,preparedinanidenticalmannerexcept70μLoftheprecursorrequiringonlytheformationofasingleσbond,comparedtosolwasdroppedontoa2.25cm2areamaskedo?ona1.5×theσandπformedduringOevolution.Weshowthatthe2.54cm2pieceofFTO.2kineticandthermodynamicadvantageofchlorideoxidationMaterialsCharacterization.X-raydi?raction(XRD)wasallowsforfasterratesofholetransfercomparedtowaterperformedonaPanalyticalEmpyreandi?ractometeroperatingoxidation.Furthermore,theHxWO3electrodesshowgreaterat1.8kW(45kV,40mA)usingCuKα(λ=1.5418?)inθ?θphotostabilityduringchlorideoxidation,whichwehypothesizegeometry.X-rayphotoelectronspectroscopy(XPS)measure-resultsfromrapidelectroninjectionfromchloride,therebymentswerecollectedonaKratosAxisUltraX-rayphoto-preventingabuild-upofsurfaceholesthatoxidizeW5+donorelectronspectrometerusingmonochromatedAlKαX-raysstates.Wesupportthishypothesisbydemonstratingthehigh(1486.7eV)atananalysischamberpressureof10?9Torr.stabilityofHxWO3duringoxidationofsodiumsul?te,anotherSamplechargingduringanalysiswascompensatedforbyusingrapidlyoxidizedsubstrate,andbyapplyingaFeOOHanelectron?oodgun.DatawasanalyzedusingCasaXPSelectrocatalystthatshowssimilarenhancementsinstability.softwareandaShirley-typebaselinewasemployedtocalculateThecalculatedvalence-bandedgeofFeOOHis2.11Vvspeakareas.Bindingenergiesweredeterminedbysettingthe19NHE,andthiselectrocatalystisknownfore?cientholeadventitiouscarbonsignalto284.8eV.UV?vismeasurements20?22collectionwhenlayeredonmetaloxidesemiconductors.wereperformedusingaCary5000spectrophotometer(Agilent)inre?ectancemodewithanintegrationspherefor■METHODSdi?usere?ectance.SolutionUV?vismeasurementswereChemicals.Inallexperiments,thewaterwas?lteredbyaperformedinabsorbancemodeusinga700μLmicrocuvette.Millipore?ltrationsystem(18.2MΩ·cm?1).Ethanol(200Transmissionelectronmicroscopysampleswerepreparedproof)waspurchasedfromDeconLaboratories.PhosphoricusinganFEIHelios650Nanolabfocusedionbeam(FIB)acid(85%w/w)waspurchasedfromEMDMillipore.workstation.TransmissionelectronmicrographsandenergyAmmoniummetatungstate((NH4)6H2W12O40·xH2O,AMT),dispersiveX-rayspectroscopy(EDS)datawerecollectedwithpoly(ethyleneglycol)(Mw=300Da,PEG-300),1000ppmaJEOL2100probe-correctedanalyticalelectronmicroscopeinICPstandardsfortungsten,hydrogenperoxide(30%w/w),STEMmodeat200kV.STEMimageswereacquiredwithasodiumchloride,andsodiumnitratewerepurchasedfromHAADFdetector.ScanningelectronmicrographswereSigma-Aldrich.TheFeSO4·7H2OwaspurchasedfromtheJTcollectedusingaJEOLJSM-7800FLV?eldemissionscanningBakerChemicalCompanyandpuri?edbydissolvingin0.5Melectronmicroscope(FESEM)operatingatanacceleratingH2SO4at50°Candthenprecipitatedwithethanol.Thevoltageof15.00kVusingeitheranEverhart-Thornleycrystalliteswereseparatedfromthemotherliquorwithasecondaryelectrondetectororafour-quadrantbackscatterBu?chnerfunnelandthenwashedwithicewater.Thepuri?edelectrondetector.FeSO4·7H2OcrystalliteswerespreadinaPetridishandPhotodepositionoftheFeOOHElectrocatalyst.Aallowedtodryovernightinthebackofafumehood.Thegalvanostaticanodicdepositiontechniquewasusedtodeposit?uorinetinoxide(FTO,PilkingtonGlassTEC-15)substratetheFeOOHelectrocatalystontotheHxWO3semiconductor.Awascutinto2.54×2.54cm2squaresforHWOspincoat405nmLEDlightsource(OsramSylvania,LZ1-10UB00-x3synthesis.TheFTOsubstratewas?rstcoarselycleanedby01U7)wasusedtobacksideilluminatetheHxWO3?lmsduringdepositionatanintensityof100mW·cm?2.Thescrubbingwithanacetone-wettedKimwipe.Thiscleaningprocedurewasfollowedbysonicatinginthefollowingsolvents:depositionsolutionwascomposedof10mMFeSO4·7H2Oinacetone,Sparkleendetergent,water,andacetoneagainfor100.1MNa2SO4atpH4.5.Theexposedelectrodeareawas4.3mineach,witheachsolventwashfollowedbydryingunderacm2andananodiccurrentdensityof75μA·cm?2waspassed8544https://doi.org/10.1021/acs.jpcc.0c11282J.Phys.Chem.C2021,125,8543?8550

2TheJournalofPhysicalChemistryCpubs.acs.org/JPCCArticleFigure1.Side-onEDSmappingofFeOOHdepositedontoHxWO3.ThesignalfromtheFeKαtransitioncanbedetectedthroughouttheentiretyoftheoxidelayers.AFeimpurityisalsodetectedintheFTOlayer.for1000s.Thedepositioncellusedwasasingle-compartment■RESULTSANDDISCUSSIONcompression-sealedcellmachinedfromPVCplastic.FilmCompositionandMorphology.IntercalatedPhotoelectrochemistry.Allphotoelectrochemistryex-5+protonswithassociatedWdonorstatesleadustowriteperimentswerecarriedoutusingaCHInstrumentsSeriestheformulaasHxWO3forthesynthesized?lms,wherexisthe760EelectrochemicalworkstationandaNewport-Oriel150WnumberofdonorstatesarisingfromprotonintercalationandXearclampa?xedwithanAM1.5Gsimulatingsolar?lteroxygenvacancies.XPSanalysisshows2.2mol%W5+inthe(Newport,P/N81094).ThePtwirewasusedasacountersynthesized?lms.2However,HWOisnotelectrochemicallyx3electrodeandthereferenceelectrodeusedwasAg/AgClininnocent,andtheW5+canbeoxidizedtoW6+withsaturatedKClwithaVycorfrit.Thepowerdensitywassimultaneousdeintercalationofprotonsintosolutionaccord-adjustedusingathermopiledetector(Newport,P/N818P-ingtothereaction015-19)andanopticalpowermeter(Newport,P/N1918-R).+?Thecellusedwasacustom-designedcompressioncellthathasHWO(s)x33FWO(s)++xxH(aq)e(7)2beendescribedpreviously.DuringmeasurementsofoxygenTheoxidationofW5+donorstatesmayoccurduringOERproduction,aNa?onmembranewasinsertedtoseparatetheworkingelectrodecompartmentfromthecounterelectrodeoperationandresultsinthedecayofphotocurrentthatis2compartmentandpreventthereductionofoxygenonthetypicallyobservedwithtungstenoxidematerials.ThelossofW5+donorscanbephotochemicallyreversedbyallowingtheplatinumcounterelectrode.DetectionofOxidizedChlorideProducts.Todeter-WO3?lmtositinAM1.5Gilluminationattheopencircuit,5+2minewhetherchlorideoxidationisthepredominantreactionregeneratingtheWdonors.ItshouldbenotedthattheoccurringonthesurfaceofHxWO3duringcontrolledpotentialelectrochemicalintercalationofprotonsintotungstenoxide23materialsactuallyresultsinthelossofphotoactivity.coulometry(CPC)experimentsina0.5MsodiumchloridePhotochemicalandelectrochemicalprotonintercalationelectrolyte,astarch?iodinetestwasused.Thistestissensitiveevidentlyproceedthroughdi?erentmechanisms.TheUV?tobothdissolvedchlorineandhypochlorousacid.Atwo-visdi?usere?ectanceisshowninFigureS1oftheSupportingcompartmentcellwasusedwithaNa?onmembraneInformation.Theabsorptiononsetbeginsat450nmandpeaksseparatingthetwohalvesand35mLofthepH4,0.5Mat364nm.ATaucplotoftheHxWO3di?usere?ectancedatasodiumchlorideelectrolytewasusedineachcompartment.ispresentedinFigureS2oftheSupportingInformationandaTheworkingelectrodecompartmentwassealedtightlybeforebandgapof2.8eVismeasured.AFeOOHelectrocatalystwasstartingtheexperiment.A1hCPCexperimentwasthendepositedontoHxWO3fromiron(II)sulfateinpH4.5carriedoutat1.23VvsRHEunder2sunAM1.5Gsolutiontoinvestigatethemechanismbywhichthephoto-illumination.FollowingCPC,25mLoftheresultingworkingcurrentdensitymaybestabilized.ThedepositedironcompartmentelectrolytewasremovedandcombinedwithelectrocatalystisamorphousbyXRD(FigureS3,SI)andpotassiumiodidetomakeasolutionwithaniodideICP-MSanalysisshowsaninitialironloadingof0.237±0.003concentrationof50mM.ThepotassiumiodidereactswithμmolFe3+·cm?2.Theside-onEDSmapsinFigure1showthatdissolvedchlorineaccordingtotheequationtheironisdistributedthroughouttheentire?lmthickness,extendingfromthetopsurfaceofthe?lmdowntotheFTO??2I(aq)+→+Cl(aq)22I(aq)2Cl(aq)substrate.ThedepositionofFeOOHdoesnotchangethemorphologyoftheunderlyingsemiconductor?lm(FigureS4,orwithhypochlorousacidaccordingtotheequationSI)bySEM,withnoobviousfeaturesappearingafterFeOOHdeposition.XPSanalysisoftheHxWO3andHxWO3|FeOOH?+HClO(aq)++2I(aq)H(aq)?lmsisshowninFigureS5oftheSupportingInformation.DoubletlinesfortheHWOW(4f)signalsfromW5+andW6+→++Cl(aq)?I(aq)HO(l)x322areobserved.FollowingFeOOHdeposition,theW(4f)W5+linesarenotdistinguishable,indicatingthatthesurfaceW5+isInbothreactions,thereisa1:1correspondencebetweentheoxidizedduringFeOOHdeposition.TheHxWO3O(1s)2-electronchlorideoxidationproduct(Cl2orHClO)andI2.regionshowstwochemicalenvironmentsforoxygenaswellFromthisresulting25mLsolution,5mLwastitratedwith10asabroadsignalforoxygenatedspeciesintheadventitiousmMNa2S2O3andastarchindicator.Thethiosulfatereducescarbon.AfterFeOOHdeposition,anewO(1s)peakemerges,thegeneratediodineaccordingtotheequationandFe(2p)featuresareobserved.TheFe(2p)signaldoesnot2??2?exhibitnoticeableshiftsafterexperimentsinNaClorNaNO3I(aq)22+→2SO3(aq)2I(aq)+SO46(aq)electrolytes.8545https://doi.org/10.1021/acs.jpcc.0c11282J.Phys.Chem.C2021,125,8543?8550

3TheJournalofPhysicalChemistryCpubs.acs.org/JPCCArticleWaterOxidationatpH4.HWO-based?lmswerefromHWO,thelossofW5+donorsthrougheq7isx3x3analyzedinpH4solutionsofa0.5Msodiumnitratesuppressed.electrolyte.Flow-cellgaschromatography(GC)wasusedtoICP-MSanalysisshowsthattheironloadingwasinitiallymeasuretheFaradaice?ciencyoftheOER(FE).Theleft0.237±0.003μmolesFe3+·cm?2,anditdecreasesto0.097±OERaxisinFigure2correspondstotherateofOERmeasuredby0.001μmolesFe3+·cm?2afterthe3hCPCat1.23VvsRHE.WhiletheFecontentdecreasedbyover50%duringthe3hCPCexperiment,boththephotocurrentandmeasuredrateofOERexhibitednegligibledecay,indicatingthatboththeoverallphotoactivityandmeasuredrateofOERdonotshowastronglinearrelationshipwiththeFeloading.Fromthisdata,weconcludethatnotallofthedepositedironcontributestotheobservedphotoactivity.XPSdata(FigureS5,SI)showsthattheFe(2p)signalisstillpresentfollowingCPCinNaNO3withnoappearanceofashoulderatlowerbindingenergies,indicatingthatnoreducedFe2+resultedfromOERoperation.ChlorideOxidationatpH4.ThepropensityforHxWO3andHxWO3|FeOOHtocarryoutchlorideoxidationwasmeasuredinthe0.5MsodiumchloridesolutionsettopH4withhydrochloricacid.TherateofOERwasmeasuredinthechlorideelectrolytetodeterminetheextentofcompetingFigure2.OERactivityonHxWO3(black)andHxWO3|FeOOH(red)chlorideoxidation.Becausetheonlyspeciesinsolutionactiveat1.23VvsRHEwithAM1.5Gilluminationin0.5MNaNO3atpHtowardoxidationarewaterandchlorideanions,anylossof4.ThecurrentdensitymeasuredduringCPC(rightaxis)wasOERactivityisassignedtotheoxidationofchloride.Figure3convertedtotherateofOER(leftaxis)forthetheoreticalrate(dashedtraces).Themeasuredrate(solidtraces)wasdeterminedby?ow-cellgaschromatography.GC(solidtraces),whiletherightaxiscorrespondstothemeasuredphotocurrentdensity(dashedtraces).ThedatainblackcorrespondtothatrecordedonHxWO3;FEOERmeasuredfromthreetrialsis87±2%,greaterthanwhatwepreviouslyreportedinapH1sulfuricacidsolution(70±210%).Thestartingphotocurrentdensityis0.47±0.03mA·cm?2,anditisdecreasedbyhalfto0.25±0.04mA·cm?2after3hofcontrolledpotentialcoulometry(CPC)at1.23VvsRHE.Aswasseenpreviouslywiththesulfateelectrolyte,usinganitrateelectrolyteresultsinthelossofphotocurrent,2consistentwiththereactionineq7.AfterformingHxWO3|FeOOH,theOERactivitywasFigure3.OERactivityonHxWO3andHxWO3|FeOOHin0.5MmeasuredagaininapH40.5MNaNO3solution.TheredNaClatpH4.OtherexperimentalconditionsandgraphicalnotationstracesofFigure2showastartingphotocurrentdensityofarethesameasthosedescribedinthecaptionofFigure2.0.417±0.009mA·cm?2.AnegligiblelossofphotoactivityoccurredduringtheCPCexperimentandthe?nalphoto-?2showsthatFEOERonHxWO3insaltwaterisonly2±1%,currentdensitywas0.41±0.01mA·cm.TheapplicationofhintingthatholetransferbetweenHxWO3andthesolutionisFeOOHtotheHxWO3materialpreventedtheseverelossofoccurringbychlorideoxidation.Thisresultiscon?rmedusingphotocurrentseenwithHxWO3alone.Wepreviouslyreportedastarch?iodinetesttodetecttheoxidizedproducts.theincreasedstabilityoftungstenoxidefollowingdepositionofComparingthetotalchargepassedduringtheCPCexperimentFeOOH,althoughtheexactmechanismwasuncertainatthe(4.3C,CPCshowninFigureS6oftheSI)againstthevolume24time.TheFeOOHelectrocatalystincreasesFEOERintheof10mMthiosulfatetitrated(315±5μL)showsthatHxWO3sodiumnitrateelectrolyteto100±1%,butnoincreaseintheis100%selectiveforthetwo-electronoxidationofchlorideinastartingphotocurrentisobserved.ThisresultsuggeststhatthepH4,0.5MNaClelectrolytewithnoOERoccurring.ThisrateofholetransferonFeOOHisnotsubstantiallyfasterthanresultisinagreementwiththepreviouswork.25,26TheUV?visonHxWO3itself;however,FeOOHdoesreducethespectrumofthesolutionintheworkingcompartmentoftheoverpotentialfortheOERasevidencedbytheincreasein0.5MelectrolyteisshowninFigureS7oftheSupportingFEOER.ThisincreaseinselectivityfortheOERhintsataInformationandsuggeststhatthepredominantproductchangeinmechanism,whichourgrouprecentlycon?rmed.formedislikelyhypochlorousacid.TheλmaxvaluesforCl2,OERonHxWO3proceedsthroughahydroxylradicalHClO,andClO?are229,233,and290nm,respectively.27intermediate(eq5),whileOERonFeOOHandHxWO3|WhiletheλmaxvaluesforCl2andHClOarecloseatapHof4,FeOOHdoesnotformanydetectablehydroxylradical.1328wedonotexpectCl2tobeformed.FormingahydroxylradicalrequiresalargeappliedpotentialBecauseOERonHxWO3requirestheformationofthe(2.7V);however,FeOOHdoesnotrequirethisintermediatehydroxylradicaltoproceed,chlorideoxidationhasbothatoperformOER,allowingforrapidholetransferfromthekineticandthermodynamicadvantageoverwateroxidation.underlyingHWOwithapathwayforrapidremovalofholesThecurrentdensitystartsat0.60±0.10mA·cm?2andx38546https://doi.org/10.1021/acs.jpcc.0c11282J.Phys.Chem.C2021,125,8543?8550

4TheJournalofPhysicalChemistryCpubs.acs.org/JPCCArticledecreasesby5%to0.57mA±0.08mA·cm?2.AnincreaseindensitydoesnotshowthelargedecaythatweobservewhenstabilityinsaltwaterisobservedbecauseoftherapidratewiththeOERisthedominantreaction.Moreover,theLSVtracewhichchloridecaninjectelectronsintoHxWO3,whichtakenafterthis16hexperimentshowsamorenegativepreventstheoxidativeprotondeintercalationreactiontophotocurrentonsetpotentialandaveryslightincreaseintheformHxWO3(eq5).saturatedphotocurrentdensitywhencomparedtotheinitialTheFeOOHelectrocatalystwasagainusedtoinvestigateLSVtracerecorded(FigureS10,SI).ThesetwofeaturesholetransferonHxWO3.Afterdepositionofanironindicatethattherateofelectroninjectionfromthesul?teelectrocatalyst(Figure3,redtraces),thephotocurrentdensityanionisfastenoughthattheHxWO3materialisactuallyin0.5MNaClisessentiallyunchanged,whileFEOERincreasesslightlyreducedratherthanoxidizedduringthisreaction.to23±1%.Theinitialphotocurrentis0.57±0.06mA·cm?2Improvingthephotoelectrochemicalstabilityofsemiconductorandshowsexcellentstability,endingat0.57±0.06mA·cm?2electrodesbycarefullyselectingthesubstratehasbeenafter3h.Asacontrolexperiment,theFeOOHelectrocatalystdemonstratedbeforewithcadmiumchalcogenideelectrodes.wasdepositedoncleanFTOwithnosemiconductorlayerandThephotoelectrochemicalstabilityofthecadmiumchalcoge-exhibitedFEOERof23%(FigureS8,SI)inasolutionof0.5Mnidescanbesigni?cantlyenhancedbyaddingaqueousNaClatpH4.OurresultsshowthattheHWOsurface32?34x3reducingagentssuchashydroquinone,iodide,andsul?te.exhibitsnopreferenceforwateroxidationinthepresenceofThesesubstratesimprovephotoelectrochemicalstabilitybythechlorideion,whileHxWO3|FeOOHexhibitsthesamerapidlyinjectingelectronsbeforedeleteriousphotocorrosionFEOERastheFeOOHcontrolin0.5MNaClatpH4.sidereactionscanoccur.TheenhancementinstabilitytrendsTogether,theseresultssuggestthatFeOOHiscapableofwiththereductionpotentialoftheoxidizedsubstrate;themorerapidlyremovingholesawayfromtheHxWO3?solutionnegativethereductionpotential,thegreaterthephoto-interfacesuchthatchemistryoccursattheFeOOH?solution35electrochemicalstability.interface.IfholetransferwerestilloccurringattheHxWO3?Theresultsfromthecadmiumchalcogenidesemiconductorssolutioninterface,theFEOERwouldbeexpectedtofollowthetranslatetoHxWO3,whereweobservedincreasedstabilitybyfollowingrelationshipprovidingasubstratethatreactsfastereitherduetothermodynamics(sul?te)orkinetics(chloride).Theshiftinη=?0.02(1θ)+0.23θ(8)FaradaicFEOERfrom87to2%whenswitchingfromthenitratetowhereθisthesurfacecoverageoftheironcatalystand0.02chlorideelectrolytesupportsthisassertion;chlorideoxidationand0.23aretheFaradaice?cienciesfortheOERonHxWO3proceedsmuchfasterthanwateroxidation.ThisshiftinFEOERandFeOOHin0.5MNaClatpH4,respectively.However,isaccompaniedbyasigni?cantincreaseinphotocurrentstability.NotablethoughisthatboththeClO?/Cl?and?Cl/thebehaviorweobserveisconsistentwithcompletesurfaceCl?couplesaremorenegativethanthe?OH,H+/HOcouple,coverage(θ=1)despitealowquantityofironcatalystloading.2ICP-MSshowsaninitialloadingof0.237±0.003μmoleFe·allowingforarapidtransferofvalence-bandholesbeforetheycm?2andXPSanalysis(FigureS5,SI)showsminimalcanperformtheslowerwateroxidationreactionthroughan?OHintermediate.EISmeasurementsinFigureS11oftheattenuationoftheW(4f)signal,indicatingthatFeOOHSupportingInformationshowthatW5+fromdonorsinHWOsurfacecoverageislow.TheOERactivitydatainFigures2andx33arerepresentativeoftheothertwotrialsshownintheispreserved.Whenthe0.5MsodiumnitrateelectrolyteisusedSupportingInformation(FigureS9,SI).ina3hCPCexperiment,shiftsareseenintheBodephaseSul?teOxidationonHxWO3atpH4.Sodiumsul?teisaplot,andanincreaseinthetotalimpedancemagnitudeisseenredox-activespeciesthatiskineticallyandthermodynamicallyintheBodeplotatlowfrequencies,suggestingamoreoxidizedfavoredforoxidationoverwater.29?31Sul?teasanoxidationHxWO3material.WhenCPCiscarriedoutinthe0.5Msubstrateisthensimilartochloride,andthephoto-sodiumchlorideelectrolyte,thereisanexcellentoverlapoftheelectrochemicalstabilityshouldbesimilarforbothions.Bodephaseandmagnitudeplots,whichsuggeststhattheFigure4showstheCPCtraceofHxWO3ina1MNa2SO3compositionoftheHxWO3surfaceislargelyunperturbedbysolutionat1.23VvsRHEfor16h.Sulfuricacidwasusedtophotoelectrochemicalchlorideoxidation.setthesolutiontoapHof4.Over16h,thephotocurrentMechanisticImplicationsofAddingFeOOH.Figure5showstheLSVtracesrecordedbeforeandaftertheCPCexperimentsonHxWO3.TheinitialLSVtracerecordedin0.5MNaNO3(solidblacktrace)showsthefootofthewavenear0.3VvsAg/AgClandsaturatesat0.80VvsAg/AgCl,whichisapproximately1.23VvsRHE.Followingthe3hCPCat1.23VvsRHEin0.5MNaNO3,theLSVresponse(dashedblacktrace)atpH4showsasimilarpro?lebutatamuchlowercurrentdensityatallpotentials,andthecurveshiftstoamorepositivepotentialforallfeaturesinthecurrentpro?le.Thecurrentdensityat0.80VvsAg/AgClwasinitially0.48mA·cm?2anddecreasedto0.27mA·cm?2atthesamepotentialduetotheoxidationofW5+donorstatesduringtheCPCexperiment.ThelossofW5+alsoresultsintheshiftinthefootofthephotocurrentresponsebecausethematerialhasbecomemoreoxidized.Whentheelectrolytecontains0.5MNaCl,theinitialLSVFigure4.CPCexperiment(16h)ofHxWO3poisedat1.23VvsRHE(solidbluetrace)showsamorenegativepotential(～0.15VvsunderAM1.5Gilluminationin1MNa2SO3atpH4.Ag/AgCl)forthefootofthephotocurrentresponseduetothe8547https://doi.org/10.1021/acs.jpcc.0c11282J.Phys.Chem.C2021,125,8543?8550

5TheJournalofPhysicalChemistryCpubs.acs.org/JPCCArticlenitrateelectrolyte.ThislossofphotocurrentdensityismuchlessthanthatobservedwithHxWO3inthesameelectrolyte,duetotheremovalofsurfaceholesbyFeOOH,whichpreventsoxidationofW5+donorstates.Using0.5MNaClastheelectrolytewithHxWO3|FeOOHalsoresultsinaminorchangeintheLSVtracebeforeandafterCPCduetoacombinationofsurfaceholeremovalbyFeOOHandbyfastchlorideoxidation.Theinitialphotocurrentat0.80VvsAg/AgClis0.59mA·cm?2andshowsaveryslightdecreaseto0.57mA·cm?2after3hofCPCat1.23VvsRHE,highlightingthepreservationofdonorstatesinHxWO3bychlorideoxidation.AddingtheFeOOHelectrocatalystincreasesthestability,asittoorapidlyremovesholesfromtheHxWO3material.Becausethevalencebandoftungstenoxideresidesat3VvsNHE,thereisgenerallyaveryhighoverpotentialfortheoxidativechemicalreactionbeingtargeted.Asaresult,theFigure5.LSVtracesrecordedinthesameelectrolyteastheCPCreactionkineticsattheelectrodearegenerallyignoredwhenexperimentplotsofHxWO3before(solidlines)andimmediatelyafterconsideringrate-determiningfactorsandresearchfocuses(dashedlines)3hCPCat1.23VvsRHEunderAM1.5Ginsteadonthephotophysicalcharacteristics(lightabsorptionillumination.Theelectrolytesare0.5MNaNO3(black)and0.5M36+NaCl(blue)atpH4.andelectron/holemobility).TheO2/H2O,Hcouple(eq2)occursat1.23VNHE,andthissuggestsanoverpotentialof1.73lowerpotentialrequiredforchlorideoxidation.Thephoto-V.Muchofthatoverpotentialisrequiredbecauseofthehigh-13currentat0.8VvsAg/AgClisinitially0.60mA·cm?2andisenergyhydroxylradicalintermediate(eq5,2.7VNHE).Theapproachingsaturation,althoughthestartofthislimitisless300mVdi?erencebetweenthevalence-bandholeenergyandwellde?nedasitisinthecaseofOERin0.5MNaNO3.forminghydroxylradicalisnotlargeenoughtoassumethatFollowing3hCPCat1.23VvsRHEin0.5MNaCl,theLSVelectrodekineticsdonotlimitphotocurrent.Thisidearesponse(dashedbluetrace)showsasimilarpro?leandacombinedwiththeCPCdataandLSVdatacollectedinthisphotocurrentthatis0.55mA·cm?2at0.80VvsAg/AgCl.TheworkusingNaNO3andNaClelectrolytesonHxWO3andlossofsaturatedphotocurrentisnotasseverewhencomparedHxWO3|FeOOHelectrodesleadstothemechanismsillustratedtowhentheelectrolytewas0.5MNaNO3.Figure6showsinScheme1.Scheme1.HxWO3StabilityisA?ectedbytheRateofInterfacialHoleTransferWheninterfacialholetransferisslowasitisintheOERonHxWO3withredox-innocentNaNO3astheelectrolyte,abuild-upofphotogeneratedholesoccursonthesurfaceofHxWO3.TheFEOER=87±2%,withphotogeneratedholesrecombiningwithconduction-bandelectronsoriginatingfromFigure6.LSVtracesrecordedinthesameelectrolyteastheCPCHxWO3donorstates.ThisundesirablerecombinationpathwayexperimentplotsofHxWO3|FeOOHbefore(solidlines)andisevidencedbythelossofHxWO3photocurrentdensityimmediatelyafter(dashedlines)3hCPCat1.23VvsRHEunderobservedintheCPC(Figure2,blacktraces)andLSV(FigureAM1.5Gillumination.Theelectrolytesare0.5MNaNO3(red)and5,blacktraces)plots.Byusingchloride,asubstratethatgets0.5MNaCl(green)atpH4.oxidizedfaster,orbyapplyingaFeOOHelectrocatalyst,therateofholetransfersubstantiallyincreases,whichreducestheimprovedstabilityinHxWO3photocurrentdensityuponconcentrationofsurfaceholesandtherebyreducesthedepositingtheFeOOHelectrocatalyst.TheLSVtracesarerecombinationrate.ThischangeisobservedastherecordedbeforeandaftertheCPCexperimentsonHxWO3|preservationofthesteady-statephotocurrentdensity.ToFeOOH0.5MNaNO3(redtraces)and0.5MNaCl(greenfurthersupporttheillustrationsinScheme1,theTafelkineticstraces).WithFeOOHdeposited,theonsetpotentialforthe(FigureS12,SI)ofHxWO3andHxWO3|FeOOHwerephotocurrentresponseconvergedto～0.2VvsAg/AgClformeasuredinthe0.5MNaNO3andNaClelectrolytesunderbothelectrolytesolutions.When0.5MNaNO3istheillumination.ThedataaresummarizedinTable1.electrolyte,theinitialcurrentdensity(solidredtrace)at0.8ThegreatestdecayinphotocurrentdensityisobservedforVvsAg/AgClis0.42mA·cm?2anddecreasesto0.41mA·cm?2HWOinthe0.5Mnitrateelectrolyte,andtheTafelslopeisx3(dashedredtrace)after3hofCPCat1.23VvsRHEinthelargest,90mV·dec?1.PerformingphotoelectrochemicalOER8548https://doi.org/10.1021/acs.jpcc.0c11282J.Phys.Chem.C2021,125,8543?8550

6TheJournalofPhysicalChemistryCpubs.acs.org/JPCCArticleTable1.TafelDataonHxWO3PhotoelectrodesStephenMaldonado?DepartmentofChemistry,UniversityofMichigan,AnnArbor,Michigan48109-1055,UnitedelectrodeelectrolyteTafelslope(mV·dec?1)States;orcid.org/0000-0002-2917-4851HxWO30.5MNaNO390Completecontactinformationisavailableat:HxWO30.5MNaCl60https://pubs.acs.org/10.1021/acs.jpcc.0c11282HxWO3|FeOOH0.5MNaNO370HxWO3|FeOOH0.5MNaCl50AuthorContributionsThemanuscriptwaswrittenthroughthecontributionsofallauthors.Allauthorshavegivenapprovaltothe?nalversionofinthe0.5MnitrateelectrolyteonHxWO3requiresthelargestthemanuscript.increaseinthepotentialtoincreasethecurrentdensity(rateofholetransferfromsolutiontotheelectrode).BydepositingaNotesFeOOHelectrocatalyst,changingtheoxidationsubstrateinTheauthorsdeclarenocompeting?nancialinterest.solutiontochloride,ordoingboth,theTafelslopedecreases,■signifyingachangeintherate-determiningelementarystepofACKNOWLEDGMENTSthereaction.ThisworkwassupportedbytheU.S.DepartmentofEnergy,O?ceofScience,BasicEnergySciences,underAwardsDE-■CONCLUSIONSSC0006587(CatalysisScience)andDE-SC0006628(SolarComparingchlorideoxidationvstheOERonHWOPhotochemistry).A.G.B.-A.thankstheHoraceH.Rackhamx3demonstratesthatwhiletheconcentrationofdissolvedGraduateSchoolattheUniversityofMichiganforaRackhamchlorideislowerthanliquidwater,thekineticsimplicityofMeritFellowship.J.J.C.thankstheUniversityofMichiganchlorideoxidationresultsinanear-completelossofFEEnergyInstituteforsummerresearchfellowships.TheauthorsOERwhentheelectrolyteischangedfrompH40.5MNaNOacknowledgethe?nancialsupportoftheUniversityof3(FEOER=87±2%)topH40.5MNaCl(FEOER=2±1%).AMichiganCollegeofEngineeringandNSFgrant#DMR-starch?iodinetestcon?rms100%Faradaice?ciencyfor9871177and#DMR-0723032andtechnicalsupportfromthechlorideoxidationinpH4,0.5MNaCl.Furthermore,MichiganCenterforMaterialsCharacterization.HxWO3exhibitsmuchgreaterstabilityinphotocurrentdensity■over3hofCPCat1.23VvsRHEwhenoxidizingthechlorideREFERENCESanioncomparedtowater.Therapidkineticsofchloride(1)Claudel,F.;Dubau,L.;Berthomé,G.;Sola-Hernandez,L.;oxidationtransferholesbeforerecombinationwithconduc-Beauger,C.;Piccolo,L.;Maillard,F.DegradationMechanismsofOxygenEvolutionReactionElectrocatalysts:ACombinedIdentical-tion-bandelectronsfromHxWO3donorstatescanoccur,LocationTransmissionElectronMicroscopyandX-RayPhoto-maintainingthehighdonordensityofthematerial.ThisresultelectronSpectroscopyStudy.ACSCatal.2019,9,4688?4698.iscorroboratedwithsul?teoxidation,anotherrapidlyoxidized(2)Breuhaus-Alvarez,A.G.;DiMeglio,J.L.;Cooper,J.J.;Lhermitte,substrate,whichalsoshowsenhancedphotocurrentstabilitybyC.R.;Bartlett,B.MKineticandFaradaicEfficiencyofOxygenasimilarmechanism.AddingFeOOHtothesurfaceofHxWO3EvolutiononReducedHxWO3Photoelectrodes.J.Phys.Chem.Cshowsasimilarphenomenonduetothescavengingof2019,123,1142?1150.photogeneratedholesinHxWO3bytheFeOOHelectro-(3)Lee,D.K.;Choi,K.-S.EnhancingLong-TermPhotostabilityofcatalystbeforerecombinationcanoccur.BiVO4PhotoanodesforSolarWaterSplittingbyTuningElectrolyteComposition.Nat.Energy2018,3,53?60.■(4)Barwe,S.;Weidner,J.;Cychy,S.;Morales,D.M.;Dieckh?fer,S.;ASSOCIATEDCONTENTHiltrop,D.;Masa,J.;Muhler,M.;Schuhmann,W.Electrocatalytic*s?SupportingInformationOxidationof5-(Hydroxymethyl)FurfuralUsingHigh-Surface-AreaTheSupportingInformationisavailablefreeofchargeatNickelBoride.Angew.Chem.,Int.Ed.2018,57,11460?11464.https://pubs.acs.org/doi/10.1021/acs.jpcc.0c11282.(5)Zhang,N.;Zou,Y.;Tao,L.;Chen,W.;Zhou,L.;Liu,Z.;Zhou,UV?visdi?usere?ectancespectrumandassociatedB.;Huang,G.;Lin,H.;Wang,S.ElectrochemicalOxidationof5-Taucplot,XRDpattern,SEMimages,XPSdata,CPCHydroxymethylfurfuralonNickelNitride/CarbonNanosheets:data,includingreplicates,BodeplotsofEISdata,andReactionPathwayDeterminedbyInSituSumFrequencyGenerationTafelplots(PDF)VibrationalSpectroscopy.Angew.Chem.,Int.Ed.2019,58,15895?15903.(6)Desilvestro,J.;Gr?tzel,M.PhotoelectrochemistryofPolycrystal-■AUTHORINFORMATIONlinen-WO3.J.Electroanal.Chem.InterfacialElectrochem.1987,238,CorrespondingAuthor129?150.BartM.Bartlett?DepartmentofChemistry,Universityof(7)Debiemme-Chouvy,C.;Hua,Y.;Hui,F.;Duval,J.-L.;Cachet,H.Michigan,AnnArbor,Michigan48109-1055,UnitedStates;ElectrochemicalTreatmentsUsingTinOxideAnodetoPreventorcid.org/0000-0001-8298-5963;Email:bartmb@Biofouling.Electrochim.Acta2011,56,10364?10370.(8)Dionigi,F.;Reier,T.;Pawolek,Z.;Gliech,M.;Strasser,P.umich.eduDesignCriteria,OperatingConditions,andNickel-IronHydroxideAuthorsCatalystMaterialsforSelectiveSeawaterElectrolysis.ChemSusChemAndrewG.Breuhaus-Alvarez?DepartmentofChemistry,2016,9,962?972.(9)Lhermitte,C.R.;Sivula,K.AlternativeOxidationReactionsforUniversityofMichigan,AnnArbor,Michigan48109-1055,Solar-DrivenFuelProduction.ACSCatal.2019,9,2007?2017.UnitedStates(10)Worrell,E.;Phylispen,D.;Einstein,D.;Martin,N.EnergyUseQuintinCheek?DepartmentofChemistry,UniversityofandEnergyIntensityoftheUSChemicalIndustry;LBNL-44314;Michigan,AnnArbor,Michigan48109-1055,UnitedStatesLawrenceBerkeleyNationalLaboratory:Berkeley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