Following chemical reactions. The ECE mechanism

Whilst it is clearly the case that double electrodes offer a unique way of studying these reactions, in many cases information can be extracted from single electrodes much of the theoretical basis was derived before the use of double electrodes became widespread. The reaction scheme may be written as 

When k is very small, the voltammetric response corresponds to an nr electron transfer and when k is very large to an (nj + n2)-electron transfer in a single wave. For intermediate k, we can obtain kinetic information. 

The problem was considered at the rotating disc electrode, making the assumptions of equal diffusion coefficients, that nx = n2 — n and that the second electron transfer is easier than the first to give [209, 210] 

In this case, analysis has to proceed by fitting experimental data from a wide range of rotation speeds to theoretical working curves. 

At the DME, a rigorous numerical solution was obtained by Nicholson et al. using the model of the expanding plane electrode [212]. This has been followed by a number of studies on expanding-plane and expanding-sphere models together with derivation of current—potential curves [213—215]. The so-called parallel ECE mechanism, where one of the electrode reactions is a reduction and the other oxidation, has been investigated and a numerical solution obtained [216]. Numerical solutions have been found to other ECE-type mechanisms at the DME [217—219]. 

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