Square-wave voltammetry of an EC reaction of a partly adsorbed redox couple

Abstract

The theory of an EC mechanism with partial adsorption of the redox couple is developed. The theoretical response is studied under conditions of square-wave voltammetry (SWV). The theoretical treatment comprises all the relevant phenomena such as diffusion mass transport, adsorption equilibrium and the kinetics of the following irreversible chemical reaction. It is presumed that the following chemical reaction occurs in the vicinity of the electrode rather than on the electrode surface itself. The adsorption of both species of the redox couple obeys a linear adsorption isotherm law. The solutions for the surface concentrations for both oxidized and reduced forms of the redox couple are presented as integral equations, thus they are valid for any chronoamperometric technique. A comparative study between the voltammetric properties of the reaction studied and the other type of EC mechanisms as well as the simple redox reaction of a partly adsorbed redox couple is presented. Special attention is paid to revealing discrepancies between the surface EC mechanism and the EC mechanism of a partly adsorbed redox couple aiming to establish criteria for distinguishing the following chemical reactions occurring on the electrode surface (surface chemical reaction) and in the bulk solution (volume chemical reaction).