Computed current density in the case of slow charge-transfer coupled with a second order chemical reaction, under potentiostatic conditions (Sn IV/Sn II system)

Abstract

Current-time curves at constant potential on plane and spherical electrode have been computed by numerical integration of the transport equations in the case of a slow charge-transfer coupled with a chemical reaction leading to a non-reactive product E 3, following the scheme: E 1+ e→E 2 E 1+ E→E 2⇔E 3 Results indicate that this mechanism is characterized by lower current densities than those of simple diffusion-transfer control. The current density is not proportional to depolarizer E 1 concentration. The main characteristic of these systems is that, when polarograms are analysed in terms of log k versus potential E, different straight lines are obtained depending on the concentration of the depolarizer; consequently, the apparent transfer coefficient α varies with concentration. Moreover all lines intersect at a same point lying at a potential near the equilibrium value, where the charge-transfer rate constant k is sufficiently small to be rate determining.