Electroreduction of bromate anion on inactive RDE under steady-state conditions: Numerical study of ion transport processes and comproportionation reaction

Abstract

The study is devoted to analyzing the electroreduction of bromate anion BrO ^-₃ on catalytically inactive (e.g., carbon) electrodes by numerical methods. This process is realized due to the combination of the reversible mediator pair Br₂/Br^- and the process of comproportionation (reaction of bromate and bromide anions) in solution phase. These reactions increase the concentration of bromine and bromide near the electrode surface; hence, this process is autocatalytic (EC″ mechanism). Within the framework of this study, a numerical algorithm which allows the system of diffusion-kinetic equations to be solved for this system is proposed for one-dimensional transport and the process under steady-state conditions. The results are compared with the conclusions of the approximate analytical theory published in Electrochim. Acta, 2015, vol. 173, p. 779, which allows inferring that both approaches are correct. The deviation between the latter is observed only in the cases of violation of approximations lying in the basis of the corresponding analytical relationships. Thus, the predictions of the analytical theory of practical interest can be considered as reliably confirmed by numerical calculations, particularly, the prediction on the nonmonotonous dependence of the maximum current on the diffusion layer thickness (or the RDE rotation rate) including the anomalous region of this dependence in which the current increases with the increase in the diffusion layer thickness.