Reverse pulse voltammetry and double potential step chronoamperometry as useful tools for characterization of electroactive systems under the conditions of mixed diffusional and migrational transport

A numerical model for reverse pulse voltammetry and double potential step chronoamperometry is presented for the systems with mixed diffusional and migrational transport. The calculations that have been done using this model indicate that under the conditions of moderate deficiency or absence of supporting electrolyte the ratio of the plateau current magnitudes, predicted for reverse pulse voltammetry, depends on the type of electrode reaction. For each type of electrode process, this ratio is also a function of support ratio (the ratio of bulk concentrations of supporting electrolyte and analyte). It has been found that for any concentration of supporting electrolyte the ratio of the magnitudes of the plateau currents changes linearly with the reciprocal of the square root of the pulse time. Such dependencies can be used to detect the contribution of migration to the current measured and to determine the diffusion coefficient of the primary substrate. The determination of these quantities requires the registration of only one double potential step chronoamperometric curve or several reverse pulse voltammograms. The reported possibilities should be especially useful for the cases where the support ratio is unknown or an addition of supporting electrolyte is impossible, e.g., for solid-state electrochemistry. For the purpose of validation of the model presented, an expression for the diffusional reverse pulse current at a hemispherical microelectrode has been derived analytically, and experimental measurements for a model redox system (ferrocene) have been performed.