KINETICS OF ELECTROLYSIS OF TRANSITION-METAL HEXACYANIDE FILMS AND REDUCTION OF SILVER FERRICYANIDE

The rate of electrolysis of thin films of Prussian blue and ruthenium purple is reconsidered in view of the realization that, ip the equation for the net current flux, the diffusion current for the electrons is opposed by that for potassium ions. Under the assumption of strong ion-electron coupling, the diffusion term drops out of the equation for the net flux and the current is driven by the potential gradient across the film. Further assumptions lead to the derivation of a current-time curve based on a concentration-dependent conductivity. Current-time data are reported in terms of an exponential relaxation time. The electrolytic mobility is obtained from the voltammetric peak separation under conditions where the film composition is uniform. Experimental data are presented for the reduction and oxidation of thin films of silver ferricyanide. The voltammograms are highly asymmetric, and it is shown that this is due to a difference in the relaxation times for oxidation and reduction.