Simulation-based strategy to distinguish between EC (reversible) and EC (dimerization) mechanisms in square-wave voltammetry

Abstract

Square-wave voltammetry (SWV) is a highly sensitive and widely utilized electrochemical technique suitable of probing the kinetics of various electrochemical electrode processes coupled with different chemical reactions. However, its application to electrode mechanisms involving subsequent chemical steps is somewhat limited, particularly in scenarios such as those discussed in recent work [1]. Among the electrochemical mechanisms coupled with chemical reactions, the EC-type pathways, where an electron transfer step is followed by a reversible chemical transformation, remains fundamental for elucidating interfacial reaction dynamics. A significant variant of this mechanism is the EC(dimerization) model. This mechanism features a reversible bimolecular chemical step in which two oxidized species (2Ox ⇌ Ox–Ox) get in reversible dimerization, while introducing second-order kinetics into the entire electrode reaction. Although mechanistically distinct, these two pathways often yield similar voltammetric signatures, making them difficult to distinguish under certain experimental conditions. This challenge is further complicated by the fact that frequency modulation, a commonly used diagnostic tool in SWV, simultaneously influences both the electron transfer kinetics and the chemical reaction rate, thus diminishing its discriminatory power. In this work, we examine the key voltammetric features of both mechanisms under SWV conditions and propose theoretical strategies to differentiate them. Emphasis is placed on the use of numerical simulations as a robust and reliable approach for resolving mechanistic ambiguity.