Quantitative analysis of the electrochemical performance of multi-redox molecular electrocatalysts. A mechanistic study of chlorate electrocatalytic reduction in presence of a molybdenium polyoxometalate

Abstract

The quantification of the performance efficiency of a given molecular electrocatalyst versus a particular substrate of interest requires the determination of the rate constants of the catalytic steps taking place in the overall reaction pathway. In this paper, a theoretical model is presented for the quantitative analysis of the voltammetric response of multi-redox catalysts, that is, a molecular species with different redox states that can act in different electrocatalytic forms as a function of the applied potential. The rigorous theoretical model presented incorporates mass transport effects and it is applicable to disc electrodes of any size. As a model system, the electro-reduction of the anion chlorate by the polyoxometalate PMo12O403- (POM) is analysed at gold electrodes. The overall process implies ten charge transfer steps and three different two-electron catalytic processes, the formal potentials and rate constants of which are accurately determined, respectively. The logarithm of the rate constants for the three catalytic steps follows a linear relationship with the average formal potentials of the two-electron charge transfer processes. A comparison with previous efforts devoted to the characterisation of electrocatalytic responses is also carried out, pointing out the advantages of a rigorous solution for this problem.