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

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 E₃, following the scheme:E₁+e→E₂E₁+E→E₂?E₃Results 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 E₁ 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.