COUPLED HOMOGENEOUS CHEMICAL REACTIONS

Coupled homogeneous chemical reactions 82 Theoretical modelling 83... 

Many interesting processes occurring at the liquid/liquid interface involve coupled homogeneous chemical reactions. In principle, electrochemical methods used for probing complicated mechanisms at metal electrodes (61) can be employed at the ITIES. However, many of these techniques (e.g., rotating ring-disk electrode or fast-scan cyclic voltammetry) are hard to adapt to liquid/liquid measurements. Because of technical problems, few studies of multistep processes at the ITIES have been reported to date (1,62). 

We have seen in this section how microelectrodes can be used in a variety of ways to study both coupled homogeneous chemical reactions and heterogeneous electron transfers. We have also seen one example of a study of metal deposition. The development of microelectrodes has made possible... 

A similar treatment can be given for other chemical reactions coupled to the charge-transfer reaction (4). This approach is often useful in formulating a qualitative or semi-quantitative interpretation of i-E curves. Notice, however, that unless explicit expressions for mR and p can be given in a particular case, the exact values of k cannot be determined. The rigorous treatment of electrode reactions with coupled homogeneous chemical reactions is discussed in Chapter 12. 

ELECTRODE REACTIONS WITH COUPLED HOMOGENEOUS CHEMICAL REACTIONS... 

Chapter 12. Electrode Reactions with Coupled Homogeneous Chemical Reactions... 

Chapter 12. Electrode Reactions with Coupled Homogeneous Chemical Reactions TABLE 12.1.1 Approximate Time Windows for Different Electrochemical Techniques... 

Several Different Coupled Homogeneous Chemical Reactions in Voltammetry... 

The popularity of the cychc voltammetry (CV) technique has led to its extensive study and numerous simple criteria are available for immediate anal-j sis of electrochemical systems from the shape, position and time-behaviour of the experimental voltammograms [1, 2], For example, a quick inspection of the cyclic voltammograms offers information about the diffusive or adsorptive nature of the electrode process, its kinetic and thermodynamic parameters, as well as the existence and characteristics of coupled homogeneous chemical reactions [2]. This electrochemical method is also very useful for the evaluation of the magnitude of imdesirable effects such as those derived from ohmic drop or double-layer capacitance. Accordingly, cyclic voltammetry is frequently used for the analysis of electroactive species and surfaces, and for the determination of reaction mechanisms and rate constants. 

In such timescales, it is possible to study very fast heterogeneous electron transfer rate constants [48]. Diffusion layers as thin as a few nanometers are characteristic for such fast scan rates [50]. Coupled homogeneous chemical reaction steps become less important, and highly reactive intermediates can be detected [48]. The chemical reversibility of electrode reactions increases and thus redox potentials of electron transfer reactions involving extremely unstable species become available [48]. 

The final term in Eq. (58) is present when analyzing electron transfer processes that include a coupled homogeneous chemical reaction. For example, for first-order decay of i, the term is negative, m = 1, n =... 

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