ON COUPLING OF INTERFACIAL AND DIFFUSIONAL IMPE-DANCES,AND ON EQUIVALENT CIRCUIT OF AN ELECTRO-CHEMICAL CELL

It is shown that the Warburg (diffusion) impedance is coupled to the charge transfer resistance, even to the extent that the sign of the Warburg impedance is determined by that of the charge transfer resistance. Experimental data obtained with the polarographic reduction of In (III) in aqueous NaSCN solution illustrate the existence of a negative Warburg impedance. The coupling between the diffusional and interfacial impedances (that is, between homogeneous mass transport and heterogeneous mass consumption or production) appears to be quite a general one, present with both redox and desad phenomena. Several graphical representations of the frequency-dependence of the electrode admittance or impedance are discussed, and the advantages of the complex capacitance plane are illustrated. © 1969.