Internal-reflection spectroelectrochemistry

To learn that the most common errors encountered with in situ UV-visible spectroelectrochemistry are those resulting from total internal reflection (TIR), which causes ringing , and by working at wavelengths beyond the band edge. 

Figure 28. Configurations for spectroelectrochemistry. A) optically transparent electrode B) optically transparent thin-layer electrode (OTTLE) C) Internal reflection spectroscopy, and D) specular reflectance spectroscopy.

Figure 44. Electrode systems for spectroelectrochemistry (a) optically transparent electrode, (b) electrode for internal reflection spectroscopy, and (c) electrode for specular reflectance spectroscopy.

Figure 17.1.17 Cell assembly for internal reflection spectroelectrochemistry. [Adapted from N. Winograd and T. Kuwana, J. Electroanal Chem., 23, 333 (1969), with permission.]...

The first infrared spectroelectrochemistry was reported in 1966 by Harry Mark and Stan Pons (30). As a postdoc at Cal Tech with Fred Anson, Mark (Figure 6) had visited Kuwana at Riverside — a visit that sparked his interest in spectroelectrochemistry. He also visited the electrochemistry group at the Science Center where he discussed internal reflection spectroelectrochemistry with Hansen. Upon his arrival at the University of Michigan as an assistant professor, Mark decided to try to develop infrared internal reflection spectroelectrochemistry because of the structural information in an infrared spectrum. He was able to persuade Paul Wilks (Wilks Scientific Corp.) to lend him a double beam internal reflectance attachment. A Ge internal reflectance plate-electrode was made by Recticon Corp. from n-type semiconducting Ge, which was already known to function as a working electrode (31,32). Stan Pons, a first year graduate student, performed the experimental work in which the spectra of the reduction products of 8-quinolinol and tetramethylbenzidine free radical were chracterized. 

Infrared Spectroelectrochemistry, Fig. 1 Schematic representation of external reflectirai left) and internal reflection (right). Note that electrolyte gap and thin film electrode are drawn dispropOTtionately thick. The... 

IR spectroelectrochemistry has been the subject of a sizeable amount of early reviews, where the experimental details and applications have been described [5-7]. Regardless the fact that electrochemistry is an extremely broad field, the following discussion will be restricted to classical electrochemical systems where a solid electrode is in contact with a liquid electrolyte solution which may contain electroactive species. Since the typically used electrolyte solutions (mostly aqueous solutions) are strongly IR absorbing, it is not possible to use a standard laboratory electrochemical cell, but for spectroelectrochemical experiments, special cell designs and beam paths have to be employed. There are two general principles on how the IR beam is directed to the electrode surface called internal reflection and external reflection, respectively. 

In the reflection mode, typically specular reflectance is measured on the electrode surface. It is anticipated that the variation of the surface structure (e.g., surface adsorption, phase transitions, etc.) will result in appreciable changes in the reflectivity properties. One can thus correlate the structural characterislics gleaned from spectroscopic measurements with electrochanical results. Figure 2.15 shows a cell assembly for internal reflection spectroelectrochemistry. Several spectroscopic techniques have been used, such as infrared, surface plasmon resonance, and X-ray based techniques (reflectivity, standing wave, etc.). Figure 2.16 depicts a cell setup for (A) infrared spectroelectrochemistry (IR-SEC) and (B) surface X-ray diffraction. 

Figure 2.15 Cell assembly for internal reflection spectroelectrochemistry (25, 26).

Figure 1 Schematic diagram of spectroelectrochemical techniques at an optically transparent electrode (OTE). (A) Transmission spectroelectrochemistry (B) transmission spectro-electrochemistry with an optically transparent thin-layer electrode (OTTLE) cell (C) internal reflection spectroscopy (IRS). Reprinted by courtesy of Marcel Dekker, Inc. from Heineman WR, Hawkridge FM and Blount HN (1984) Spectroelectrochemistry at optically transparent electrodes. II. Electrodes under thin-layer and semi-infinite diffusion conditions and indirect coulometric titrations. In Bard AJ (ed) Electroanalytical Chemistry. A Series of Advances, Vol 13, pp 1-113. New York Marcel-Dekker.

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