Voltammetry for surface-active ions at polarisable liquid|liquid interfaces

Adsorption of charged species at the interface between two immiscible electrolyte solutions (ITIES) is simulated taking into account both the mutual influence between the potential dependent surface excess charge and the potential distribution between the two phases and the partition equilibrium of the surface-active molecules. The electrical potential profiles are calculated assuming a single adsorption plane separating two electrical diffuse layers following the modified Verwey–Niessen model (MVN). The interfacial boundary potential is obtained from the electroneutrality condition. The interplay between adsorption and partition under steady-state conditions is addressed yielding voltammetric responses for the adsorption–desorption processes along with the faradaic response.     

Square Wave Voltammetry and Voltcoulometry applied to electrocatalytic reactions. Oxidation of ferrocyanide at a ferrocene modified gold electrode

The electrochemical response of an electrocatalytic process taking place at a redox mediator modified electrode has been analysed with Square Wave Voltammetry (SWV) and Square Wave Voltcoulometry (SWVC) for which, a simple expression of the current and converted charge have been deduced for the usual experimental situation of high catalytic rate constants. Both techniques give rise to peak-shaped responses whose peak parameters have been deduced in the case of reversible electrochemical step. The influence of key parameters such as the square wave pulse amplitude, the rate constant of the chemical step and the reversibility of the charge transfer has been studied. Moreover, the SWVC charge–potential curves allow an immediate determination of the catalytic rate constant, independently of the value of the electrochemical rate constant. The theoretical predictions have been tested with the electrocatalytic oxidation of ferrocyanide mediated by a mixed 6-(ferrocenyl)hexanethiol-hexanethiol monolayer at a disk gold electrode, and an excellent agreement between theory and experiments has been found.