Optical transparent electrode

Optically transparent electrodes (OTEs), which enable light to be passed through their surface and the adjacent solution, are the keys for performing transmission... 

FIGURE 2-10 Thin-layer spectroelectrochemical cell. OTE = optically transparent electrode. 

W Heineman, F. Hawkridge and H. Blount, Spectroelectrochemistry at Optically Transparent Electrodes in A.J. Bard, Ed., Electroanalytical Chemistry, Vol. 13, Marcel Dekker, New York, 1986. 

Ohmic drop, 32, 88, 105, 129 Operational amplifier, 105 Optically transparent electrode, 40 Organic-phase biosensors, 181 Organic solvents, 102 Organosulfur monolayers, 118 Overvoltage, 14, 121 Oxygen, 75, 87, 103, 177, 190, 193... 

Fig. 5.19 (a) Linking CdSe quantum dots to Ti02 particle with bifunctional surface modifier (b) light harvesting assembly composed of T102 film functionahzed with CdSe Q-dots on optically transparent electrode (OTE). [Adapted (in gray scale) from [348]]... 

Figure 33.1a illustrates the idea of the smart window. In this device a layer of electrochromic material and a layer of a transparent ion-conducting electrolyte are sandwiched between two optically transparent electrodes (OTEs). Indium-doped tin oxide on glass is used most commonly as the OTE. This material has very low... 

Relatively little work has been done on ORR catalysis by self-assembled mono-layers (SAMs) of metalloporphyrins. The advantages of this approach include a much better defined morphology, structure, and composition of the catalytic film, and the surface coverage, and the capacity to control the rate at which the electrons ate transferred from the electrode to the catalysts [CoUman et al., 2007b Hutchison et al., 1993]. These attributes are important for deriving the catal5d ic mechatfism. The use of optically transparent electrodes aUows characterization of the chemical... 

Electrochemically generated products can be readily characterized by in situ measurement of their absorption spectra in the ultraviolet and visible regions. Optically transparent electrodes (OTEs) prepared from thin layers... 

Fig. 17.10 Electron transport in pristine Ti02 (left) and rG0-Ti02 nanocomposite (right) films cast on an optically transparent electrode (OTE). Reprinted with permission from [55]. Copyright 2012, American Chemical Society.

To learn that in situ spectroeiectrochemistry requires optically transparent electrodes, be aware of the usual materials for making them, and how and why an in situ cell is constructed. 

In general, two (similar) approaches are used to construct an optically transparent electrode (OTE). 

Figure 8.3 Illustration of in situ spectroelectrochemistry, showing a set of UV-vis ( electronic ) spectra of solid-state Prussian Blue (iron(ii,iii) hexacyanoferrate(ii)) adhered to an ITO-coated optically transparent electrode. The spectra are shown as a function of applied potential (i) —0.2 (ii) -1-0.5 (iii) -1-0.8 (iv) -1-0.85 (v) -1-0.9 (vi) +1.2 V (all vs. SCE). From Mortimer, R. J. and Rosseinsky, D. R., J. Chem. Soc., Dalton Trans., 2059-2061 (1984). Reproduced by permission of The Royal Society of Chemistry.

The most common cause of trouble when working with optically transparent electrodes (OTEs) is scratches in the thin film of conductor. Since the electrode is coated with a thin layer of semiconductor, a scratch can in effect cut right through the conductive layer, thus causing an insulatory channel. The two parts of the semiconductor on either side of the scratch are therefore prevented from communicating with each other, and so the portion of the electrode beyond the scratch is rendered useless. 

To learn how to lest if an optically transparent electrode made of indium-tin oxide (ITO) is dirty or over-reduced, and therefore unsuitable for electroanalyses, Just by visual examination. 

However, most of the electroanalyst s experiments require solid electrodes, which naturally fall within two categories, namely either inert electrodes such as platinum, gold and glassy carbon, or redox electrodes such as copper, lead or magnesium. We will also consider optically transparent electrodes in this discussion. 

Optically transparent electrodes. In situ spectroelectrochemistry was discussed in the previous chapter. The most common materials for constructing optically transparent electrodes for use in such analyses are thin films of semiconducting oxide deposited on to glass. Such materials are readily available commercially. 

How do we make a contact with an optically transparent electrode or a low-melting-point metal such as lead ... 

Figure 9.2 Schematic diagram showing how an electrical contact is fixed with silver paint to the conductive side of an optically transparent electrode. The outer layer of epoxy resin is necessary to impart strength, to insulate the silver paint from the analyte solution and to stop analyte solution seeping between the paint and the conductive layer.

Indium-tin oxide (ITO) Tin-doped indium oxide, used as a thin solid film on glass when constructing optically transparent electrodes. 

Optically transparent electrode (OTE) An electrode used for in situ spec-troelectrochemistry. 

Interest has developed in electrochromic light transmission modulators, which are called smart windows , for control of temperature and lighting in buildings and automobiles. A cross section of an electrochromic light transmission modulator is shown in Fig. 11.31 (Rauh and Cogan, 1988). The two electrochromic elements of the structure are designated ECl and EC2, and are sandwiched between two thin film, optically transparent, electrodes of ITO and separated by an electrolyte. The ECl layer should colour when a negative potential is applied and the EC2 layer should either colour under positive potentials or remain in a transparent state. This is indicated by the chemical reactions ... 

Electrolytic capacitors Optically transparent electrodes Antistatic coalings... 

Several devices based solely on the compound have been prepared [27], usually involving a solid phase sandwiched between two optically transparent electrodes. An example is an arrangement of two ITO electrodes with a membrane of a solid polymer electrolyte (Nafion) [112] in between on which Prussian blue has been chemically generated. 

In a typical spectroelectrochemical measurement, an optically transparent electrode (OTE) is used and the UV/vis absorption spectrum (or absorbance) of the substance participating in the reaction is measured. Various types of OTE exist, for example (i) a plate (glass, quartz or plastic) coated either with an optically transparent vapor-deposited metal (Pt or Au) film or with an optically transparent conductive tin oxide film (Fig. 5.26), and (ii) a fine micromesh (40-800 wires/cm) of electrically conductive material (Pt or Au). The electrochemical cell may be either a thin-layer cell with a solution-layer thickness of less than 0.2 mm (Fig. 9.2(a)) or a cell with a solution layer of conventional thickness ( 1 cm, Fig. 9.2(b)). The advantage of the thin-layer cell is that the electrolysis is complete within a short time ( 30 s). On the other hand, the cell with conventional solution thickness has the advantage that mass transport in the solution near the electrode surface can be treated mathematically by the theory of semi-infinite linear diffusion. 

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