STUDY OF ELECTRODE REACTIONS

Evans D FI 1991 Review of voltammetric methods for the study of electrode reactions Microelectrodes Theory and Applications (Nate ASI Series E vol 197) ed M I Montenegro, M A Queiros and J L Daschbach (Dordrecht Kluwer)... 

The concepts and basic approach used in studies of electrical fluctuations in corrosion processes proved to be very successful as well in mechanistic studies of electrode reactions taking place at materials covered by passivating films. A typical example is the electrochemical dissolution of silicon. From an analysis of the noise characteristics of this process, it has been possible to identify many features as well as the conductivity of the nanostructures of porous silicon being formed on the original silicon surface. 

The low-temperature electrochemistry technique is useful in the study of electrode reactions involving unstable products or intermediates. Lowering the temperature by 30-40 °C decreases the reaction rate of the unstable species to one-tenth of the original value. It is equivalent to a ten-fold increase in the voltage scan rate. Figure 8.22 shows the effect of temperature on the cyclic voltammo-gram for the oxidation of 1,2,3,6,7,8-hexahydropyrene. At ambient temperatures, it does not give a re-reduction peak Fiowever, at -60 °C, reversible oxidation and rereduction waves are observed. The techniques of low-temperature electrochemistry... 

Thin-layer voltammetry (TLV) is a very slow technique, and this fact is used to great advantage in quantitative studies of electrode reactions with small heterogeneous rate constants. This area has been pioneered and reviewed by Hubbard [29,30]. TLV is also applicable to examination of metal deposition and... 

Since the limiting current is proportional to concentration, a rotating-disk electrode can be used for analytical purposes (but almost never is in practice). In summary, the rotating disk electrode is one of the valuable techniques available for the fundamental study of electrode reactions as evidenced by its substantial popularity. 

The application of thin-layer spectroelectrochemical techniques to the study of electrode reactions in molten salts is becoming increasingly popular. Experiments have been conducted in both the ultraviolet-visible and infrared spectral regions. Background information about thin-layer spectroelectrochemical techniques is given in Chapter 3. In addition, Norvell and Mamantov [72] have reviewed the application of spectroelectrochemical techniques to molten salts. 

This chapter concerns the study of electrode reaction mechanisms of inorganic and organometallic complexes. The emphasis is on proper use of experimental measurables from cyclic voltammetry for diagnosis of common mechanisms such as E, EC, CE, and ECE reactions. We employ the standard designation of electron transfer (et) reactions as E, and other chemical reactions as C. In practice, mechanistic studies make use of an array of electrochemical and other physical and chemical methods, but space limitations restrict our attention to the powerful and versatile technique of cyclic voltammetry (CV). If necessary, the reader may review the fundamentals of this technique in Chapter 3. 

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