A preliminary search for interfacial light absorption caused by faradaic electron transfer
✍ Scribed by G.C. Barker
- Publisher
- Elsevier Science
- Year
- 1972
- Weight
- 241 KB
- Volume
- 39
- Category
- Article
- ISSN
- 0022-0728
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✦ Synopsis
Considerable interest has been exhibited in recent years in the optical properties of the electrode-solution interface 1. Ellipsometric and reflectance studies have been made using, in the main, solid metal or semi-conductor electrodes. Reflectance spectroscopy, although not the oldest of the experimental methods, is the most obvious one to employ and, in principle, studies are made of the reflectance or differential reflectance as a function of potential using preferably light of different wavelengths.The potentialities of optical methods have been discussed recently by Plieth 2. The modulation techniques used by Bewick and Tuxford 3, by McIntyre and Kolb 4 and by other workers offer clear advantage for the precise measurement of very small changes in reflectance in the presence of light amplitude changes due to artefacts such as slow changes in the intensity of the light source. While this simple development is important, especially in the context of solid electrodes, it is possible that the technique outlined below has certain advantages when the electrode material is mercury. The technique in question is very closely related to simple modulation reflectance spectroscopy and is one used some years ago in a search for light absorption connected with light-induced electron transfer from the electrode to species present at the interface.
Although still not generally recognised, it is desirable whenever possible to use a dropping mercury electrode, if mercury is to be employed, to minimise surface contamination. While charcoal purification methods, that evolved from a pre-war platinized platinum procedure of the Frumkin school, have been developed at this Establishment s , it has to be admitted that such methods, even in skilled hands, do not invariably result in adequate freedom from all types of contamination. In unskilled hands contamination by inorganic impurities, such as fine particles of carbon, is likely to occur. Even if this experimental barrier can be satisfactorily negotiated there remains'the problem of surface vibrations when a mercury pool electrode is employed and the potential is varied periodically at a low frequency. This further difficulty which is due to the combination of (a) non-spherical or non-cylindrical surface curvature and (b) the potential dependence of surface tension, can be avoided either by eliminating the surface curvature 6 or by using a flowing cylindrical "mercury" electrode formed by allowing mercury to flow down the surface of a vertical amalgamatable wire (silver, copper, nickel, platinum). The latter type of electrode (amalgamated silver) we have used successfully (for limited periods of time only) in studies of the dependence of light-induced electron emission on the direction of the electric vector 7. It is certain J. Electroanal. Chem., 39 (1972) '
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