Spectroelectrochemistry applications

The two reviews, Spectroelectrochemistry Applications and Spectroelectro-chemistry Methods and instrumentation , both by Mortimer, R. J., appear in The Encyclopedia of Spectroscopy and Spectrometry, Lindon, J. C., Trantor, G. E. and Holmes J. L. (Eds), Academic Press, London, 2000, pp. 2161-2174 and 2174-2181, respectively, and give excellent coverage of this combined spectroscopic and electrochemical technique. 

Applications Scattering and Particle Sizing, Applications Spectroelectrochemistry, Applications... 

See also Colorimetry, Theory Dyes and Indicators, Use of UV-Visible Absorption Spectroscopy Ellipsometry Light Sources and Optics Spectroelectrochemistry, Applications. 

Besides its widespread use for investigating the mechanism of redox processes, spectroelectrochemistry can be usefiil for analytical purposes. In particular, the simultaneous profiling of optical and electrochemical properties can enhance the overall selectivity of different sensing (30) and detection (31) applications. Such coupling of two modes of selectivity is facilitated by the judicious choice of the operating potential and wavelength. 

Semiconductors. In Sections 2.4.1, 4.5 and 5.10.4 basic physical and electrochemical properties of semiconductors are discussed so that the present paragraph only deals with practically important electrode materials. The most common semiconductors are Si, Ge, CdS, and GaAs. They can be doped to p- or n-state, and used as electrodes for various electrochemical and photoelectrochemical studies. Germanium has also found application as an infrared transparent electrode for the in situ infrared spectroelectrochemistry, where it is used either pure or coated with thin transparent films of Au or C (Section 5.5.6). The common disadvantage of Ge and other semiconductors mentioned is their relatively high chemical reactivity, which causes the practical electrodes to be almost always covered with an oxide (hydrated oxide) film. 

To a large extent, the discovery and application of adsorption phenomena for the modification of electrode surfaces has been an empirical process with few highly systematic or fundamental studies being employed until recent years. For example, successful efforts to quantitate the adsorption phenomena at electrodes have recently been published [1-3]. These efforts utilized both double potential step chronocoulometry and thin-layer spectroelectrochemistry to characterize the deposition of the product of an electrochemical reaction. For redox systems in which there is product deposition, the mathematical treatment described permits the calculation of various thermodynamic and transport properties. Of more recent origin is the approach whereby modifiers are selected on the basis of known and desired properties and deliberately immobilized on an electrode surface to convert the properties of the surface from those of the electrode material to those of the immobilized substance. 

Fig. 17 Spectroelectrochemistry of21a, formation ofthe radical anion 21a on application of-900 mV (vs. Ag/AgCI). Inset Cyclic voltammogram of 21 a in acetonitrile with 0.1 mol dirT3TBAHFP, at a Pt electrode vs. Fc/Fc+and a scan rate of 50 mV s-1.

The chemical stability and electrochemical reversibility of PVF films makes them potentially useful in a variety of applications. These include electrocatalysis of organic reductions [20] and oxidations [21], sensors [22], secondary batteries [23], electrochemical diodes [24] and non-aqueous reference electrodes [25]. These same characteristics also make PVF attractive as a model system for mechanistic studies. Classical electrochemical methods, such as voltammetry [26-28] chronoamperometry [26], chronopotentiometry [27], and electrochemical impedance [29], and in situ methods, such as spectroelectrochemistry [30], the SECM [26] and the EQCM [31-38] have been employed to this end. Of particular relevance here are the insights they have provided on anion exchange [31, 32], permselectivity [32, 33] and the kinetics of ion and solvent transfer [34-... 

Jeanmaire, D. L. and Van Duyne, R. P. (1977). Surface Raman spectroelectrochemistry Part I. Heterocyclic, aromatic, and aliphatic amines adsorbed on the anodized silver electrode. J. Electroaml. Chem. 84 1-20. Albrecht, M. G. and Creighton, J. A. (1977). Anomalously intense Raman spectra of pyridine at a silver electrode. J. Am. Chem. Soc. 99 5215-5217. Van Duyne, R. P. (1979). In Chemical and biochemical applications of lasers, Moore, C. B. (Ed.), academia press. New York, pplOl-185,... 

A. J. Bard and L. R. Faulkner, Electrochemical Methods Fundamentals and Applications, 2nd ed., Wiley, New York, 2001 Spectroelectrochemistry Theory and Practice, R. J. Gale, ed.. Plenum Press, New York, 1988 Electrochemical Interfaces Modern Techniques for In-Situ Interface Characterisation, H. D. Abruna, ed., VCH, New York, 1991 S. Pons, J. K. Foley, J. Russell and M. Seversen, Mod. Aspects Electrochem., 1986,17,223. 

Spectroelectrochemistry utilises the difference in the spectroscopic signature between the oxidised and the reduced form of a system to probe its redox properties. An incremental application of potential gradually changes the spectral profile of a system corresponding to the changes in the population of oxidised and reduced species. These spectral changes as a function of applied potential allow for the determination of various redox properties including, the... 

Although the cyclic voltammetry for this complex seems fairly similar to the trinuclear ruthenium cluster dimers, the lower-lying LUMO (as evidenced by the lower reduction potential) of the triazine bridging ligand plays an important role in explaining the details of the spectroelectrochemistry observed for this LCD. The CO stretching frequency of the neutral complex appears at 1940 cm Upon application of— 1.050 V (vi. Ag pseudoreference, roughly 0 to... 

This overview on the use of spectroelectrochemistry within the field of carbon-rich organometallics is organised by the experimenters main purpose for conducting these experiments rather than by individual compound classes. With that, we wish to emphasise the various applications of spectroelectrochemical methods and to demonstrate their utility. Some complementary work based on chemical redox agents or bulk electrolyses and remote spectroscopic investigations is also cited to provide a more complete picture, though not in a wholly comprehensive manner. 

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