Potential sweep methods charge transfers

Linear scan voltammetry (LSV) — It is an experimental method when the -> electrode potential is varied linearly with time (t) with a scan (sweep) rate v = dE/dt and the current (I) vs. E curve (which is equivalent with E vs. t curve) is recorded. Usually scan rates ranging from 1 mV s-1 to 1V s-1 are applied in the case of conventional electrodes with surface area between 0.1 and 2 cm2, however, at -> ultramicroelectrodes 1000 or even 106 V s-1 can also be used. The scan is started at a potential where no electrochemical reaction occurs. At the potential where the charge transfer begins, a current can be observed which increases with the potential, however, after a maximum value (current peak) it starts to decrease due to the depletion of the reacting species at the -> interface. 

Linear sweep voltammetry Ep measurements have not been applied extensively for the study of heterogeneous charge transfer kinetics. A serious problem with the use of this method is that Ep in itself is not significant in this respect but rather Ep — Etev is the quantity of interest. While AEP in CV is readily measured, this cannot be said for Etev using only LSV as a measurement technique. Therefore, there does not appear to be any advantage in LSV for the study of electrode kinetics. A more detailed analysis of the LSV wave, by convolution potential sweep or normalized potential sweep voltammetry (both to be discussed later) can provide both a and k°. 

The widespread use of large-amplitude relaxation techniques in the investigations of anodic organic oxidations, requires further comment on the value of these methods. Reinmuth divided these techniques into three classes based on the types of applications quantitative kinetic studies, qualitative kinetic studies, and analytical studies. We are not concerned here with the analytical applications. For studies in kinetics, controlled-potential techniques, particularly linear-potential scan, in either single sweep or in cycles, and to some extent chronopotentiometry, have been primarily employed. Chronopotentiometry has been successfully utilized in the study of transient reactions, e.g., the reaction of CO with platinum oxide or the reaction of oxalic acid with platinum oxide, and the study of simple charge-transfer reactions with linear diffusion (cf. Refs. 159-161). However, since the general application of chronopotentiometry is severely limited for the study of anodic organic oxidations, as commented previously, this technique will not be further discussed. The quantitative analysis of data obtained by linear potential scan techniques is complicated because the form of theoretical results even for the simplest cases, requires the use of computers and consequently very little quantitative kinetic information has been obtained. This... 

Application of the Laplace transformation method to this bounded diffusion problem results, in the case of reversible charge transfer through the layer of surface area A (at a sweep rate v), in a current-potential relation of the form... 

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