β Scribed by R.D. Armstrong
No coin nor oath required. For personal study only.
Recently, Macdonald 1 has suggested an equivalent circuit (Fig. 19, ref. 1) for an electrochemical cell where (a) an infinitely rapid faradaic reaction occurs at the electrodes, and (b) an indifferent electrolyte is present. This circuit is at variance with conventional electrochemical thinking and it is the purpose of the present communication to suggest reasons for this.
The conventional equivalent circuit 2 for an electrode at which an electrochemical reaction is occurring is shown in Fig. 1, when it is assumed that:
(i) The electrode of interest, e.g. a mercury sphere, is surrounded by a large second electrode of negligible impedance.
(ii) There is an indifferent electrolyte present, e.g. 0.9 M NaF.
(iii) The components of the redox couple are present in much smaller concentrations, e.g. 10-3 M, and are not specifically adsorbed.
(iv) The electrochemical reaction occurs by a single step mechanism.
(v) The time averaged concentrations (Co, Cg) of the redox couple at the electrode surface (x = 0) obey the Nernst equation (or at x = x2 where x2 is the distance of closest approach).
In recent years the ways in which the circuit of Fig. 1 has to be changed to accommodate changes in conditions (i)-(v) have been discussed, but such considerations are irrelevant in the present context. It is however obvious that Fig.
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