Application of the unequal distances of closest approach theory to the analysis of double-layer effects on Zn(II) reduction at a mercury electrode

The orthogonal collocation technique has been applied to the development of a numerical solution of the unequal distances of closest approach (UDCA) t heory for any number of electrolytes and planes of closest approach to the electrode surface. On the basis of theoretical analysis of the reaction coo rdinate of Zn2+ reduction by Schmickler et al. (Chem. Phys. 2000, 252, 349) , a UDCA analysis of the Frumkin effect on the bserved charge-transfer rate constants has been performed. The supporting electrolytes LiClO4, Mg(ClO4) (2), and Al(ClO4)(3) were chosen to vary systematically the distance of clo sest approach of the electrolyte cation with respect to that of the electro active species. UDCA distances of closest approach derived from electrocapi llary data are shown to provide a reasonable account of the Frumkin effect. However, more consistent results are obtained when variations of the Zn2activity coefficient, computed from the MSA theory, are also considered.