Monitoring the Electrochemical Failure of Indium Tin Oxide Electrodes via Operando Ellipsometry Complemented by Electron Microscopy and Spectroscopy
Sprache des Titels:
Englisch
Original Kurzfassung:
Transparentconductiveoxidessuch as indiumtinoxide (ITO)are standardsfor thin film electrodes,providingasynergyof high opticaltransparencyand electricalconductivity.Inan electrolyticenvironment,the determinationof an inertelectrochemicalpotentialwindowis crucialto maintaina stablematerialperformanceduringdeviceoperation.We introduceoperandoellipsometry,combiningcyclic voltammetry(CV) withspectroscopicellipsometry,as a versatiletool to monitortheevolutionof both completeoptical(i.e., complexrefractiveindex)and electricalpropertiesunderwet electrochemicaloperationalconditions.In particular,we trace the degradationof ITOelectrodescausedby electrochemicalreductionin a pH-neutral,water-basedelectrolyteenvironmentduringelectrochemicalcycling.With the onset of hydrogenevolutionat negativebias voltages,indiumand tin are irreversiblyreducedto the metallicstate, causingan advancingdarkening,i.e., a gradualloss of transparency,with every CV cycle, while the conductivityis mostlyconservedover multipleCV cycles.Post-operandoanalysisrevealsthe reductive(loss of oxygen)formationof metallicnanodropletson the surface.The reductivedisruptionof the ITO electrodehappensat the solid?liquidinterfaceand proceedsgraduallyfrom thesurfaceto the bottomof the layer, whichis evidencedby cross-sectionaltransmissionelectronmicroscopyimagingandcomplementedby energy-dispersiveX-ray spectroscopymapping.As long as a continuouspart of the ITO layer remainsat thebottom,the conductivityis largelyretained,allowingrepeatedCV cycling.We consideroperandoellipsometrya sensitiveandnondestructivetool to monitorearly stage materialand propertychanges,either by tracingfailurepoints,controllingintentionalprocesses,or for sensingpurposes,makingit suitablefor variousresearchfields involvingsolid?liquidinterfacesand electrochemicalactivity.
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