Oxidation of ferrocene derivatives at a poly[Ni(saltMe)] modified electrode

Abstract

The characterisation of film permeability and mediation properties of poly[Ni(saltMe)] modified electrodes were evaluated by studying the oxidation of ferrocene and 1,1′-dimethylferrocene at these electrodes by rotating-disk voltammetry. The effects of varying the substrate and its solution concentration, film thickness, rotation speed and electrode potential on the limiting current density were analysed using the model of Albery. Both substrate oxidations show two mechanisms, according to the applied potential. The first, direct reaction on the underlying electrode is controlled by substrate transport through the film (Et S case). The second, polymer-mediated reaction occurred at higher potentials, and was the only substrate oxidation process observed for thick films. Mechanistic analysis for polymer-mediated oxidation revealed some dependence of the reaction zone on the substrate and its concentration. For the highest ferrocene concentrations, oxidation occurs in a thin reaction layer away from both interfaces (LRZt et S case). However, for the highest concentrations of 1,1′-dimethylferrocene, the mediated reaction is controlled by substrate transport through the film and occurs close to the underlying electrode interface (LEt S case). As both substrate concentrations decrease, the heterogenous rate constants for the modified electrode, k′ ME, become essentially independent of film thickness and are consistent with rate limiting electron transfer at or near the film ∣ solution interface (S k′ or LS k cases).