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》由会员上传分享，免费在线阅读，更多相关内容在学术论文-天天文库。

pubs.acs.org/JPCCArticleChlorideOxidationasanAlternativetotheOxygen-EvolutionReactiononHxWO3PhotoelectrodesAndrewG.Breuhaus-Alvarez,QuintinCheek,JoshuaJ.Cooper,StephenMaldonado,andBartM.Bartlett*CiteThis:J.Phys.Chem.C2021,125,8543−8550ReadOnlineACCESSMetrics&MoreArticleRecommendations*sıSupportingInformationABSTRACT:Acomparisonofphotoelectrochemicaloxygen-evolutionreaction(OER)andchlorideoxidationisperformedonsemiconductingHxWO3thinfilms.Overa3hcontrolledpotentialcoulometry(CPC)experiment,thephotocurrentdensityrecordedduringOERinanitrateelectrolytedecreasestohalfthestartingphotocurrent.However,ifthesameelectrolysisexperimentisperformedwithachlorideelectrolyte,thephotocurrentdensityismuchmorestable,degradingbyonly5%overthesameperiod.Linearsweepvoltammetry(LSV)inthenitrateelectrolyteexhibitsafootofthewaveapproximately150mVmorepositivethaninthechlorideelectrolyteandthesaturatedphotocurrentdensityisapproximately20%greaterinthechlorideelectrolytecomparedtothenitrateelectrolyte.Also,theFaradaicefficiency(FE)fortheOERis87±2%inthenitrateelectrolytecomparedtoanFEof100%fortheoxidationofthechlorideelectrolytetohypochlorousacid.TheseresultssuggestthatthechlorideionrapidlyinjectselectronsintothephotogeneratedholesintheHWOvalencebeforetheseholesdestructivelyrecombinewithW5+electrondonors.x3TheresultisanincreaseinHxWO3stabilityduringphotoelectrochemicalchlorideoxidationwhencomparedtowateroxidation.FeOOHelectrocatalystsareknowntoefficientlyremoveholesfromphotoresponsivemetaloxides,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%ofindustrialchemicalouttheOERondifferentelectrochemicalandphoto-processes.10,11Apartfromstronglyacidicaqueoussolutions,electrochemicalplatformstypicallyexhibitssignificantdegra-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/JPCCArticleCl2reactsinaqueousenvironmentstoproducehypochloriteflowingN2stream.Ag/AgClreferenceelectrodeswereanioninbasicsolutionsorhypochlorousacidinmoreacidicpurchasedfromCHInstrumentsandfilledwithsaturated12conditions(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-bottomflaskandthen14Chlorideoxidationmayproceedthrougharadicalaswell.adding10mLofwatertodissolvecompletelywithvigorous−•−stirring.Separately,6.6g(22mmol)ofPEG-300wasdissolvedCl(aq)→+Cl(aq)e,E°=2.6VNHE(6)in10mLofethanolinascintillationvial.TheethanolsolutionHowever,thehydroxylradicalreductionpotentialisatawasslowlyaddedtotheaqueoussolutionbyapipettewhilemorepositivepotentialthanthechlorideradicalreductionstirringvigorouslyoverthecourseofapproximately3min,potential.Therefore,chlorideoxidationisexpectedtobetheresultinginafaint,off-whitesolprecursor,whichwas0.5MinthermodynamicallyfavoredreactiononHxWO3regardlessoftungsten.ElectrodesforPECmeasurementswerepreparedbyformationofachlorideradicalisrequiredinthechloridedropping200μLoftheprecursorsolontoclean,2.54cmsquares(6.45cm2)ofFTOandthenspunat2500rpmfor30soxidationmechanism.Inthismanuscript,wedemonstratetheoxidationofchlorideusingaLaurelspincoater.Afterspincoatingalayer,thefilmbytungstenoxidegeneratedbyprocessinganammoniumwasplacedintoa500°Cmufflefurnacefor30min.Thespinmetatungstatesol,whosechemistryisbestdescribedasthecoatandannealprocedurewasrepeatedforatotalof10times2formulaHxWO3inpH4solutions.Thevalencebandoftomakethe1μmthickfilmsusedinthiswork.TheHxWO3HxWO3(3VvsNHE)issufficientlypositivetoprovidetheelectrodesusedinthedetectionofoxidizedchlorideproductsbythestarch-iodidetestwere1.5cmsquares(2.25cm2)andoverpotentialrequiredfortheoxidativereactionspresentedin15−18eqs2−6.Chlorideoxidationisalsokineticallysimpler,preparedinanidenticalmannerexcept70μLoftheprecursorrequiringonlytheformationofasingleσbond,comparedtosolwasdroppedontoa2.25cm2areamaskedoffona1.5×theσandπformedduringOevolution.Weshowthatthe2.54cm2pieceofFTO.2kineticandthermodynamicadvantageofchlorideoxidationMaterialsCharacterization.X-raydiffraction(XRD)wasallowsforfasterratesofholetransfercomparedtowaterperformedonaPanalyticalEmpyreandiffractometeroperatingoxidation.Furthermore,theHxWO3electrodesshowgreaterat1.8kW(45kV,40mA)usingCuKα(λ=1.5418Å)inθ−θphotostabilityduringchlorideoxidation,whichwehypothesizegeometry.X-rayphotoelectronspectroscopy(XPS)measure-resultsfromrapidelectroninjectionfromchloride,therebymentswerecollectedonaKratosAxisUltraX-rayphoto-preventingabuild-upofsurfaceholesthatoxidizeW5+donorelectronspectrometerusingmonochromatedAlKαX-raysstates.Wesupportthishypothesisbydemonstratingthehigh(1486.7eV)atananalysischamberpressureof10−9Torr.stabilityofHxWO3duringoxidationofsodiumsulfite,anotherSamplechargingduringanalysiswascompensatedforbyusingrapidlyoxidizedsubstrate,andbyapplyingaFeOOHanelectronfloodgun.DatawasanalyzedusingCasaXPSelectrocatalystthatshowssimilarenhancementsinstability.softwareandaShirley-typebaselinewasemployedtocalculateThecalculatedvalence-bandedgeofFeOOHis2.11Vvspeakareas.Bindingenergiesweredeterminedbysettingthe19NHE,andthiselectrocatalystisknownforefficientholeadventitiouscarbonsignalto284.8eV.UV−vismeasurements20−22collectionwhenlayeredonmetaloxidesemiconductors.wereperformedusingaCary5000spectrophotometer(Agilent)inreflectancemodewithanintegrationspherefor■METHODSdiffusereflectance.SolutionUV−vismeasurementswereChemicals.Inallexperiments,thewaterwasfilteredbyaperformedinabsorbancemodeusinga700μLmicrocuvette.Milliporefiltrationsystem(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-7800FLVfieldemissionscanningBakerChemicalCompanyandpurifiedbydissolvingin0.5Melectronmicroscope(FESEM)operatingatanacceleratingH2SO4at50°Candthenprecipitatedwithethanol.Thevoltageof15.00kVusingeitheranEverhart-Thornleycrystalliteswereseparatedfromthemotherliquorwithasecondaryelectrondetectororafour-quadrantbackscatterBüchnerfunnelandthenwashedwithicewater.Thepurifiedelectrondetector.FeSO4·7H2OcrystalliteswerespreadinaPetridishandPhotodepositionoftheFeOOHElectrocatalyst.Aallowedtodryovernightinthebackofafumehood.Thegalvanostaticanodicdepositiontechniquewasusedtodepositfluorinetinoxide(FTO,PilkingtonGlassTEC-15)substratetheFeOOHelectrocatalystontotheHxWO3semiconductor.Awascutinto2.54×2.54cm2squaresforHWOspincoat405nmLEDlightsource(OsramSylvania,LZ1-10UB00-x3synthesis.TheFTOsubstratewasfirstcoarselycleanedby01U7)wasusedtobacksideilluminatetheHxWO3filmsduringdepositionatanintensityof100mW·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+protonswithassociatedWdonorstatesleadustowriteperimentswerecarriedoutusingaCHInstrumentsSeriestheformulaasHxWO3forthesynthesizedfilms,wherexisthe760EelectrochemicalworkstationandaNewport-Oriel150WnumberofdonorstatesarisingfromprotonintercalationandXearclampaffixedwithanAM1.5Gsimulatingsolarfilteroxygenvacancies.XPSanalysisshows2.2mol%W5+inthe(Newport,P/N81094).ThePtwirewasusedasacountersynthesizedfilms.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,aNafionmembranewasinsertedtoseparatetheworkingelectrodecompartmentfromthecounterelectrodeoperationandresultsinthedecayofphotocurrentthatis2compartmentandpreventthereductionofoxygenonthetypicallyobservedwithtungstenoxidematerials.ThelossofW5+donorscanbephotochemicallyreversedbyallowingtheplatinumcounterelectrode.DetectionofOxidizedChlorideProducts.Todeter-WO3filmtositinAM1.5Gilluminationattheopencircuit,5+2minewhetherchlorideoxidationisthepredominantreactionregeneratingtheWdonors.ItshouldbenotedthattheoccurringonthesurfaceofHxWO3duringcontrolledpotentialelectrochemicalintercalationofprotonsintotungstenoxide23materialsactuallyresultsinthelossofphotoactivity.coulometry(CPC)experimentsina0.5MsodiumchloridePhotochemicalandelectrochemicalprotonintercalationelectrolyte,astarch−iodinetestwasused.Thistestissensitiveevidentlyproceedthroughdifferentmechanisms.TheUV−tobothdissolvedchlorineandhypochlorousacid.Atwo-visdiffusereflectanceisshowninFigureS1oftheSupportingcompartmentcellwasusedwithaNafionmembraneInformation.Theabsorptiononsetbeginsat450nmandpeaksseparatingthetwohalvesand35mLofthepH4,0.5Mat364nm.ATaucplotoftheHxWO3diffusereflectancedatasodiumchlorideelectrolytewasusedineachcompartment.ispresentedinFigureS2oftheSupportingInformationandaTheworkingelectrodecompartmentwassealedtightlybeforebandgapof2.8eVismeasured.AFeOOHelectrocatalystwasstartingtheexperiment.A1hCPCexperimentwasthendepositedontoHxWO3fromiron(II)sulfateinpH4.5carriedoutat1.23VvsRHEunder2sunAM1.5Gsolutiontoinvestigatethemechanismbywhichthephoto-illumination.FollowingCPC,25mLoftheresultingworkingcurrentdensitymaybestabilized.ThedepositedironcompartmentelectrolytewasremovedandcombinedwithelectrocatalystisamorphousbyXRD(FigureS3,SI)andpotassiumiodidetomakeasolutionwithaniodideICP-MSanalysisshowsaninitialironloadingof0.237±0.003concentrationof50mM.ThepotassiumiodidereactswithμmolFe3+·cm−2.Theside-onEDSmapsinFigure1showthatdissolvedchlorineaccordingtotheequationtheironisdistributedthroughouttheentirefilmthickness,extendingfromthetopsurfaceofthefilmdowntotheFTO−−2I(aq)+→+Cl(aq)22I(aq)2Cl(aq)substrate.ThedepositionofFeOOHdoesnotchangethemorphologyoftheunderlyingsemiconductorfilm(FigureS4,orwithhypochlorousacidaccordingtotheequationSI)bySEM,withnoobviousfeaturesappearingafterFeOOHdeposition.XPSanalysisoftheHxWO3andHxWO3|FeOOH−+HClO(aq)++2I(aq)H(aq)filmsisshowninFigureS5oftheSupportingInformation.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-basedfilmswerefromHWO,thelossofW5+donorsthrougheq7isx3x3analyzedinpH4solutionsofa0.5Msodiumnitratesuppressed.electrolyte.Flow-cellgaschromatography(GC)wasusedtoICP-MSanalysisshowsthattheironloadingwasinitiallymeasuretheFaradaicefficiencyoftheOER(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)wasdeterminedbyflow-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.AnegligiblelossofphotoactivityoccurredduringtheCPCexperimentandthefinalphoto-−2showsthatFEOERonHxWO3insaltwaterisonly2±1%,currentdensitywas0.41±0.01mA·cm.TheapplicationofhintingthatholetransferbetweenHxWO3andthesolutionisFeOOHtotheHxWO3materialpreventedtheseverelossofoccurringbychlorideoxidation.ThisresultisconfirmedusingphotocurrentseenwithHxWO3alone.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,whichourgrouprecentlyconfirmed.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.Afterdepositionofanironindicatethattherateofelectroninjectionfromthesulfiteelectrocatalyst(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)inasolutionof0.5MnidescanbesignificantlyenhancedbyaddingaqueousNaClatpH4.OurresultsshowthattheHWOsurface32−34x3reducingagentssuchashydroquinone,iodide,andsulfite.exhibitsnopreferenceforwateroxidationinthepresenceofThesesubstratesimprovephotoelectrochemicalstabilitybythechlorideion,whileHxWO3|FeOOHexhibitsthesamerapidlyinjectingelectronsbeforedeleteriousphotocorrosionFEOERastheFeOOHcontrolin0.5MNaClatpH4.sidereactionscanoccur.TheenhancementinstabilitytrendsTogether,theseresultssuggestthatFeOOHiscapableofwiththereductionpotentialoftheoxidizedsubstrate;themorerapidlyremovingholesawayfromtheHxWO3−solutionnegativethereductionpotential,thegreaterthephoto-interfacesuchthatchemistryoccursattheFeOOH−solution35electrochemicalstability.interface.IfholetransferwerestilloccurringattheHxWO3−Theresultsfromthecadmiumchalcogenidesemiconductorssolutioninterface,theFEOERwouldbeexpectedtofollowthetranslatetoHxWO3,whereweobservedincreasedstabilitybyfollowingrelationshipprovidingasubstratethatreactsfastereitherduetothermodynamics(sulfite)orkinetics(chloride).Theshiftinη=−0.02(1θ)+0.23θ(8)FaradaicFEOERfrom87to2%whenswitchingfromthenitratetowhereθisthesurfacecoverageoftheironcatalystand0.02chlorideelectrolytesupportsthisassertion;chlorideoxidationand0.23aretheFaradaicefficienciesfortheOERonHxWO3proceedsmuchfasterthanwateroxidation.ThisshiftinFEOERandFeOOHin0.5MNaClatpH4,respectively.However,isaccompaniedbyasignificantincreaseinphotocurrentstability.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,shiftsareseenintheBodephaseSulfiteOxidationonHxWO3atpH4.Sodiumsulfiteisaplot,andanincreaseinthetotalimpedancemagnitudeisseenredox-activespeciesthatiskineticallyandthermodynamicallyintheBodeplotatlowfrequencies,suggestingamoreoxidizedfavoredforoxidationoverwater.29−31SulfiteasanoxidationHxWO3material.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)atpH4showsasimilarprofilebutatamuchlowercurrentdensityatallpotentials,andthecurveshiftstoamorepositivepotentialforallfeaturesinthecurrentprofile.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,althoughthestartofthislimitisless300mVdifferencebetweenthevalence-bandholeenergyandwelldefinedasitisinthecaseofOERin0.5MNaNO3.forminghydroxylradicalisnotlargeenoughtoassumethatFollowing3hCPCat1.23VvsRHEin0.5MNaCl,theLSVelectrodekineticsdonotlimitphotocurrent.Thisidearesponse(dashedbluetrace)showsasimilarprofileandacombinedwiththeCPCdataandLSVdatacollectedinthisphotocurrentthatis0.55mA·cm−2at0.80VvsAg/AgCl.TheworkusingNaNO3andNaClelectrolytesonHxWO3andlossofsaturatedphotocurrentisnotasseverewhencomparedHxWO3|FeOOHelectrodesleadstothemechanismsillustratedtowhentheelectrolytewas0.5MNaNO3.Figure6showsinScheme1.Scheme1.HxWO3StabilityisAffectedbytheRateofInterfacialHoleTransferWheninterfacialholetransferisslowasitisintheOERonHxWO3withredox-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.Allauthorshavegivenapprovaltothefinalversionofinthe0.5MnitrateelectrolyteonHxWO3requiresthelargestthemanuscript.increaseinthepotentialtoincreasethecurrentdensity(rateofholetransferfromsolutiontotheelectrode).BydepositingaNotesFeOOHelectrocatalyst,changingtheoxidationsubstrateinTheauthorsdeclarenocompetingfinancialinterest.solutiontochloride,ordoingboth,theTafelslopedecreases,■signifyingachangeintherate-determiningelementarystepofACKNOWLEDGMENTSthereaction.ThisworkwassupportedbytheU.S.DepartmentofEnergy,OfficeofScience,BasicEnergySciences,underAwardsDE-■CONCLUSIONSSC0006587(CatalysisScience)andDE-SC0006628(SolarComparingchlorideoxidationvstheOERonHWOPhotochemistry).A.G.B.-A.thankstheHoraceH.Rackhamx3demonstratesthatwhiletheconcentrationofdissolvedGraduateSchoolattheUniversityofMichiganforaRackhamchlorideislowerthanliquidwater,thekineticsimplicityofMeritFellowship.J.J.C.thankstheUniversityofMichiganchlorideoxidationresultsinanear-completelossofFEEnergyInstituteforsummerresearchfellowships.TheauthorsOERwhentheelectrolyteischangedfrompH40.5MNaNOacknowledgethefinancialsupportoftheUniversityof3(FEOER=87±2%)topH40.5MNaCl(FEOER=2±1%).AMichiganCollegeofEngineeringandNSFgrant#DMR-starch−iodinetestconfirms100%Faradaicefficiencyfor9871177and#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.iscorroboratedwithsulfiteoxidation,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.;Dieckhöfer,S.;ASSOCIATEDCONTENTHiltrop,D.;Masa,J.;Muhler,M.;Schuhmann,W.Electrocatalytic*sıSupportingInformationOxidationof5-(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−visdiffusereflectancespectrumandassociatedB.;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.;Grätzel,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,CA,2000.JoshuaJ.Cooper−DepartmentofChemistry,Universityof(11)Brinkman,T.;Giner,G.S.;Schorcht,F.;Roudier,S.;DelgadoMichigan,AnnArbor,Michigan48109-1055,UnitedStatesSancho,L.BestAvailableTechniques(BAT)ReferenceDocumentforthe8549https://doi.org/10.1021/acs.jpcc.0c11282J.Phys.Chem.C2021,125,8543−8550

7TheJournalofPhysicalChemistryCpubs.acs.org/JPCCArticleProductionofChlor-alkali;PublicationsOfficeoftheEuropeanUnion:(32)Sitabkhan,F.TheEffectofIlluminationontheAnodicLuxembourg,2014.DissolutionofCadmiumSulphideinthePresenceofaRedoxSystem.(12)Perrin,D.D.IonisationConstantsofInorganicAcidsandBasesinBer.Bunsenges.Phys.Chem.1972,76,389−393.AqueousSolution;ElsevierScience:Burlington,2013.(33)Fujishima,A.;Sugiyama,E.;Honda,K.Photosensitized(13)Proctor,A.D.;Bartlett,B.M.HydroxylRadicalSuppressionElectrolyticOxidationofIodideIonsonCadmiumSulfideSingleDuringPhotoelectrocatalyticWaterOxidationonWO3|FeOOH.J.CrystalElectrode.Bull.Chem.Soc.Jpn.1971,44,304.Phys.Chem.C2020,124,17957−17963.(34)Tenne,R.;Hodes,G.PhotoelectrochemistryofCdSeinSulfite(14)Wardman,P.ReductionPotentialsofOne-ElectronCouplesElectrolyte.Ber.Bunsenges.Phys.Chem.1985,89,74−78.InvolvingFreeRadicalsinAqueousSolution.J.Phys.Chem.Ref.Data(35)Inoue,T.;Watanabe,T.;Fujishima,A.;Honda,K.-I.;1989,18,1637−1755.Kohayakawa,K.SuppressionofSurfaceDissolutionofCdS(15)Bamwenda,G.R.;Sayama,K.;Arakawa,H.TheEffectofPhotoanodebyReducingAgents.J.Electrochem.Soc.1977,124,SelectedReactionParametersonthePhotoproductionofOxygenand719−722.HydrogenfromaWO−Fe2+−Fe3+AqueousSuspension.J.Photo-(36)Butler,M.A.PhotoelectrolysisandPhysicalPropertiesofthe3chem.Photobiol.,A1999,122,175−183.SemiconductingElectrodeWO2.J.Appl.Phys.1977,48,1914−1920.(16)VandeKrol,R.;Liang,Y.;Schoonman,J.SolarHydrogenProductionwithNanostructuredMetalOxides.J.Mater.Chem.2008,18,2311−2320.(17)Bak,T.;Nowotny,J.;Rekas,M.;Sorrell,C.C.Photo-ElectrochemicalHydrogenGenerationfromWaterUsingSolarEnergy.Materials-RelatedAspects.Int.J.HydrogenEnergy2002,27,991−1022.(18)Ping,Y.;Galli,G.OptimizingtheBandEdgesofTungstenTrioxideforWaterOxidation:AFirst-PrinciplesStudy.J.Phys.Chem.C2014,118,6019−6028.(19)Yan,J.;Li,P.;lJi,Y.;Bian,J.;Li,Y.;Liu,S.Earth-AbundantElementsDopingforRobustandStableSolar-DrivenWaterSplittingbyFeOOH.J.Mater.Chem.A2017,5,21478−21485.(20)Laskowski,F.A.L.;Nellist,M.R.;Qui,J.;Boettcher,S.W.MetalOxide/(oxy)hydroxideOverlayersasHoleCollectorsandOxygen-EvolutionCatalystsonWater-SplittingPhotoanodes.J.Am.Chem.Soc.2019,141,1394−1405.(21)Kim,T.W.;Choi,K.-S.NanoporousBiVO4PhotoanodeswithDual-LayerOxygenEvolutionCatalystsforSolarWaterSplitting.Science2014,343,990−994.(22)Francas,L.;Corby,S.;Selim,S.;Lee,D.;Mesa,C.A.;Godin,̀R.;Pastor,E.;Stephens,I.E.L.;Choi,K.-S.;Durrant,J.R.SpectroelectrochemicalStudyofWaterOxidationonNickelandIronOxyhydroxideElectrocatalysts.Nat.Commun.2019,10,No.5208.(23)Calero,S.J.;Ortiz,P.;Oñate,A.;Cortés,M.EffectofProtonIntercalationonPhoto-activityofWO3AnodesforWaterSplitting.Int.J.HydrogenEnergy2016,41,4922−4930.(24)Lhermitte,C.R.;Verwer,J.G.;Bartlett,B.M.ImprovingtheStabilityandSelectivityfortheOxygen-EvolutionReactiononSemiconductingWO3PhotoelectrodeswithaSolid-StateFeOOHCatalyst.J.Mater.Chem.A2016,4,2960−2968.(25)Yourey,J.E.;Pyper,K.J.;Kurtz,J.B.;Bartlett,B.M.ChemicalStabilityofCuWO4forPhotoelectrochemicalWaterOxidation.J.Phys.Chem.C2013,117,8708−8718.(26)Hill,J.C.;Choi,K.-S.EffectofElectrolytesontheSelectivityandStabilityofn-typeWO3PhotoelectrodesforUseinSolarWaterOxidation.J.Phys.Chem.C2012,116,7612−7620.(27)Belz,M.;Boyle,W.;Klein,K.;Grattan,K.Smart-SensorApproachforaFibre-Optic-BasedResidualChlorineMonitor.Sens.Actuators,B1997,39,380−385.(28)Pourbaix,M.AtlasofElectrochemicalEquilibriainAqueousSolutions,2nded.;NationalAssociationofCorrosionEngineers:Houston,TX,1974.(29)Sarala,R.;Islam,M.A.;Rabin,S.B.;Stanbury,D.M.AromaticSulfonationbySO2‑andtheReductionPotentialoftheSulfite3Radical:OxidationofSulfitebytheTetraamine(phenanthroline)-ruthenium(III)Cation.Inorg.Chem.1990,29,1133−1142.(30)Hemmingsen,T.TheElectrochemicalReactionofSulphur-OxygenCompounds−PartI.AReviewofLiteratureontheElectrochemicalPropertiesofSulphur/Sulphur-OxygenCompounds.Electrochim.Acta1992,37,2775−2784.(31)McDonald,K.J.;Choi,K.-S.ANewElectrochemicalSynthesisRouteforaBiOIElectrodeanditsConversiontoaHighlyEfficientPorousBiVO4PhotoanodeforSolarWaterOxidation.EnergyEnviron.Sci.2012,5,8553−8557.8550https://doi.org/10.1021/acs.jpcc.0c11282J.Phys.Chem.C2021,125,8543−8550