Electrochemical Reactions and Electrode Kinetics

Cyclic voltammetry (CV) is perhaps the most versatile electroanalytical technique for the study of electroactive species. CV is usually used to characterize electrochemical reactions and electrode surface absorption, and has become increasingly popular in all fields of chemistry as a means of studying redox reaction rates in a wide potential range. CV is also a typical mefliod for the study of reaction mechanisms, as its mathematical description has been developed sufficiently to enable kinetic parameters to be determined. 

Fleig reviews fundamental aspects of solid state ionics, and illustrates many similarities between the field of solid state electrochemistry and liquid electrochemistry. These include the consideration of mass and charge transport, electrochemical reactions at electrode/solid interfaces, and impedance spectroscopy. Recent advances in microelectrodes based on solid state ionics are reviewed, along with their application to measuring inhomogeneous bulk conductivities, grain boundary properties, and electrode kinetics of reactions on anion conductors. 

The principal aims of this review are to indicate the role of chemisorbed intermediates in a number of well-known electrocatalytic reactions and how their behavior at electrode surfaces can be experimentally deduced by electrochemical and physicochemical means. Principally, the electrolytic gas evolution reactions will be covered thus, the extensive work on the important reaction of O2 reduction, which has been reviewed recently in other literature, will not be covered. Emphasis will be placed on methods for characterization of the adsorption behavior of the intermediates that are the kinetically involved species in the main pathway of the respective reactions, rather than strongly adsorbed by-products that may, in some cases, importantly inhibit the overall reaction. The latter species are, of course, also important as they can determine, in such cases, the rate of the overall reaction and its kinetic features, even though they are not directly involved in product formation. 

The processes in (1) and (2), involve a charge carrier on the surface, and depend on electrode potential, while that in (3) may not. Because of this difference, those in (1) and (2) are considered electrochemical reactions and that in (3) a chemical reaction. All these modes of charge transfer can be involved in an etching process but the relative contribution of each mode depends on the specific conditions. Identification of the charge-transfer mode and understanding of its relation to the structural and kinetic processes is a fundamental aspect of etching electrochemistry. 

Complex investigations on electrode materials and electrode kinetics were carried out with the aim to elaborate electrodes with high electrochemical activity. The route and mechanism of the electrode reactions, dependence of polarization on electrode materials and structure, gas atmosphere, and other factors were studied. As a result of this research the electrodes based on Ni, Co, Cu, manganite, and cobaltite having high working characteristics were elaborated. 

It is often necessary to apply potentials in excess of that required by thermodynamics to drive a particular electrochemical reaction when the kinetics of a redox reaction are slow at a bare electrode. This overpotential can be lowered by accelerating the rate of electrochemical reaction by modifying the electrode surface. For surface-immobilized redox sites, electrocatalysis is accomplished by shuttling electrons by repeated cycling between the catalytic and precatalytic state between the electrode and the electroactive substrate this process is known as mediated electrocataly sis. ... 

In the previous sections, the impedance behavior of electrochemical cells was described, with a view of how kinetic parameters of electrochemical reactions or electrode properties such as the morphology might be extracted from an impedance spectrum. However, electrochemical impedance spectroscopy has been utilized for a vast number of applications and is not limited to mechanistic investigations of electrode reactions. A large number of studies have been dedicated to the investigation of coated electrode surfaces. In this chapter, a few selected examples will be given of how impedance spectra of coated electrodes can be evaluated and what information can be gained from them. 

The mechanism and kinetics of electrochemical reactions at electrodes covered with PT studied using the voltammetric behavior of PT films depend on the nature and concentration of mobile charge carriers within the polymer and therefore on the potential range [193,194]. The dependence of the processes during the electrochemical reduction and oxidation on the medium in contact with the PT film can be revealed by in situ Raman spectra [195]. The doped and neutral states of PMT and poly(3-thienylacetic acid) and the anion and cation dopants can be clearly identified by an improved specular reflectance IR spectroscopy. This method allows the use of the same electrode as that used in... 

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