Step potential as a diagnostic tool in square-wave voltammetry of quasi-reversible electrochemical processes

Abstract

Abstract By applying square-wave voltammetry (SWV) and through examining the most common electrochemical kinetic region, i.e. the quasi-reversible charge transfer process, the important role of the step potential (height, ΔE) was theoretically and practically studied considering both, the dissolved as well as the electrode surface confined redox species. It was found that the impact of the step potential is readily manifested through the scan rate (v) of an SWV experiment, the one being the product of the frequency of pulses (f) and the step potential (v\xa0= ΔE f). The presented studies evidently confirmed that the role of the step potential is very complex but that it significantly affects the morphology of both, the forward as well as the backward SWV current components, which applies for any degree of electrochemical reversibility. Furthermore, it was demonstrated that in case of quasi-reversible electrochemical reactions the degree of reversibility profoundly depends on the step potential applied. Moreover, it was proven that the degree of reversibility can be markedly improved by correspondingly decreasing ΔE. This has significant importance in the context of electrode kinetics as well as in analytical applications. Hence, this study clearly demonstrated that besides the frequency, the step potential can be an additional important tool for inspecting and improving the electrode kinetics in SWV. Finally, in order to test a practical example of a quasireversible electrode reaction of a dissolved redox couple, the SWV measurements of theFe3+(aq)/Fe2+(aq) redox couple were carried out using a basal plane pyrolytic graphite electrode and the resulting readings confirmed our theoretical predictions.