Transmittance spectroscopy and optically transparent cell materials

1 Transmittance spectroscopy and optically transparent cell materials 

Transmission electronic spectroscopy, the most facile and readily available spectroscopic technique for investigating electrochemical reactions, became possible due to the availability of OTEs. The underlying principle is that the working electrode, usually solid, is optically transparent. This means that it transmits more than 50% of incident light within the wavelength region of interest. 

Prerequisites of working electrode materials for OTEs include optical transparency, amenable potential windows, and stability towards electrolyte and solvent. There are broadly two types of OTE materials in common use  

Thin films of transparent metal oxide semiconductor (e.g., indium tin oxide and fluorine doped tin oxide) deposited on a transparent medium are finding increasing application because thick films can be used due to the optical transparency of metal oxides in the visible region of the spectrum and there are fewer problems with resistance than for thin metal films. The drawback to these materials is that they do not transmit ultra violet 

The auxiliary and reference electrodes in electronic and other spectroelectrochemical experiments are similar to those used in conventional electrochemical cells. They must be small enough to fit into the cell without complicating its construction. Common auxiliary electrodes are small platinum wires, paddles, or coils. Reference electrodes (see Chapter 4) are frequently Ag/Ag+ or AgCl because these can be miniaturized. In non-quantitative appUcations, silver wire coated with AgCl or a simple silver wire as a pseudo reference (quasi-reference electrode, QRE) can be used. However, commercially available aqueous and non-aqueous Ag/Ag+ in which the electrode is separated from the analyte solution via a frit are preferable because they are more stable. The majority of electronic spectroelectrochemical experiments are conducted using OTEs in either thin layer (finite) or semi-infinite diffusion regimes. 

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