DOUBLE-LAYER EFFECTS IN THE ELECTRODE-KINETICS OF AMALGAM FORMATION REACTIONS .1. A COMPARISON OF THE EE AND IA MECHANISMS

The potential dependence of two mechanisms for reduction of a divalent cation at a mercury electrode are compared. In one mechanism it is assumed that the ion is reduced in two consecutive electron transfer steps occurring at or near the outer Helmholtz plane. In the second mechanism, the reacting ion moves into the inner layer in an ion transfer step and then to an adsorption site at the interface in an adsorption step without the transfer of a discrete electron to the reactant in the double layer. The effect of variation in the location of the reactant with respect to that of the outer Helmholtz plane, and also of partial charge transfer and an asymmetrical barrier in the adsorption step are considered in detail. It is shown on the basis of careful estimates of double layer effects, that the potential dependence of the overall rate constants for the two mechanisms are similar, and that there is no clear way to distinguish between them. It is suggested that a study of the temperature dependence of these reactions would help differentiate between the two mechanisms.