From the linear dependencies of the voltammetric capacitive current, i(c), with the potential sweep rates, nu, observed in the low and high domains, it is possible to determine the inner and outer differential capacities of oxide coatings. The morphological factor,phi, defined as the ratio of the inner and total differential capacities (C-d,C-i/Cd) shows a linear relationship with the radius/ionic charge ratio of the anion of the supporting electrolyte. The dependence of the capacitive voltammetric charge, q(c), on nu was interpreted on the basis of a purely capacitive model for the oxide/solution interface.