CECDC mechanism

Several reaction schemes can be imagined in this category, based on chemical intuition. A compilation of such reasonably realistic schemes was given in ref. 6. Here, we confine ourselves to elaborating one example, also treated in ref. 7, viz. the CECDC mechanism. 

However, it may happen that a non-linear mechanism cannot a priori be excluded. Therefore we now consider the elaboration of Rct and X for the CECDC mechanism treated in Sect. 4.2.2. It is tedious, but not difficult, to derive from eqn. (123) expressions for the partial derivatives F, O and R in terms of and the mean concentrations c and Cr. It can also be verified that these expressions reduce to simpler ones in the limiting cases for which eqn. (124) holds. The next step is to substitute c 0 and Cr by appropriate functions of c , Cr, and reversible case, this involves procedures similar to those mentioned in Sect. 4.3.1 and one may wonder whether the impedance parameters are of more diagnostic value than the d.c. current itself. 

In Fig. 32, both p and Sp have been depicted as a function of E — E° for the five particular cases of the CECDC mechanism with only one rate-... 

Explicit expressions for the second-order partial derivatives occurring in eqn. (16) for the general CECDC mechanism, cf. eqns. (36)... 

Finally, the CECDC mechanism with more than one rate-determining step is considered. By a procedure similar to that described in the previous section, but now in terms of the second-order Taylor expansions of the individual rate equations, explicit expressions for the three second-order parameters in eqn. (140) have indeed been derived [7]. Although they are not as surveyable as their first-order counterparts, the expressions compiled in Table 7 are sufficiently simple to be suitable for fitting experimental data. 

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