Randles-SevCik relationship

If the electrooxidation of AA at the platinum electrode is controlled solely by the mass transfer process in the solution (Figure 21.9), the relationship between the maximum current density at the maximum potential should obey the Randles-Sevcik law... 

Many years ago, a theoretical expression for the peak current for a reversible cyclic voltammogram was derived as a function of the scan rate to give the Randles-Sevcik expression [50] (Eq. n.1.11). According to this relationship, the dependence of the peak current. Ip, on scan rate, v, follows a characteristic square-root law, which provides a tell-tale sign of the presence of a diffusion-controlled process. 

In theory, D, c, or n can be calculated from the peak current (Ip) of a dc linear-sweep or cyclic voltammogram by employing the relationships described by the Randles-Sevcik equation for a reversible electron-transfer process of the kind Ox+ne" Red, when the effect of is negligible [6]. When woiking in a viscous RTIL, however, very few of the electrochemical systems of interest fulfill these criteria, which severely limits the direct application of dc voltammetry for this purpose. Assuming the Randles-Sevcik equation is not applicable, a best-fit approach with numerical simulation may be a viable alternative, although even this method has its limitations, as mechanistic complexities or other uncertainties can make the modeling process difficult [10]. 

The quantitative information regarding the concentration of electroactive(s) com-pound(s) can be obtained from the voltammogram using the Randles-Sevcik equation, for the case of a reversible reaction. This equation expresses the relationship between the peak current intensity /p (either anode or cathode) and the analyte concentration (C) at a given absolute temperature (T, in Kelvin or Rankine) and is given by... 

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