Theoretical study of the EE reaction mechanism with comproportionation and different diffusivities of reactants

In this article we investigate the origin of unexpected features appearing in voltammetry or double-step chronoamperometry of EE systems when the rate of comproportionation is extremely fast and the diffusion coefficients of the reactant and products highly differ. These features were noticed during the testing of our new software KISSA intended to solve any reaction mechanisms even when acute reaction fronts develop near the electrode surface or within the solution. To validate the principle of the new adaptive algorithm [C. Amatore, O. Klymenko, I. Svir, Electrochem. Commun. doi:10.1016/j.elecom.2010.06.009] implemented in KISSA we used analytical and numerical solutions for double-step chronoamperometry. This revealed that the peculiar current jumps stem from a rapid variation of the reaction front position when the starting material is still reducible at the electrode while the product of the second electron transfer is re-oxidized. The exact convergence between the predictions by these independent methods demonstrated that KISSA is perfectly accurate even under such extreme mechanistic conditions.