Theory of square-wave voltammetry for the analysis of a CE reaction mechanism complicated by the adsorption of the reactant

Abstract

This manuscript presents a theoretical work about an electrode process preceded by a chemical reaction involving adsorbed species and where both reactions can present any degree of reversibility. The electrode reaction involves an adsorbed reactant that releases the product in solution, which is a reaction mechanism that is typically found for the cathodic stripping voltammetric response of metal complexes. To the best of our knowledge this the first time that a general mathematical solution that merges the effects of diffusion, adsorption and other parameters associated with the kinetics and thermodynamics of this reaction mechanism is presented. The analysis is focused on the description of square-wave (SW) voltammetric profiles where the preceding chemical reaction involves a partially labile complex. It is important to point out that the value of frequency at the so called “quasi-reversible maximum” is not shifted due to a quasi-labile preceding chemical reaction, and that typical experimental conditions would commonly ensure the presence of inert metal complexes. In this regard, inert preceding chemical reactions have no effect on the shape of SW voltammetric responses. However, several kinetic parameters are affected by the time scale of the experiment and electrochemical reactions with a labile or quasi-labile preceding chemical step that involves adsorbed species. In this case, the system has to be experimentally shifted towards a region where the effect of the chemical reaction is (or gives the impression to be) inert to obtain mechanistic information about the electrode reaction.