Mathematical model for evaluating permeability and electrode reversibility in thin-film voltammetry. Part 1: Chronoamperometric behavior.

Abstract

Diverse systems of technologic and scientific relevance involve a surface-confined diffusional problem coupled to a charge transfer reaction and depend on similar boundary conditions. A general mathematical solution for describing electrochemical responses associated with the diffusion of electroactive species into a host thin-film (TF) material is presented. In this manuscript, the mathematical solutions correspond to chronoamperometric profiles of electrodes modified with a TF where the electroactive species have different permeability and reversibility of the charge transfer reaction.In chronoamperometric measurements, the film permeability (or the partition constant) affects the ratio between the values of current measured at long and short times of a Cottrell plot. Besides, the ratio between the film thickness and the diffusion coefficient of species inside the film affects the time when the TF behavior can be observed.The model is used to optimize the fit of chronoamperometric profiles corresponding to the oxidation of FcMeOH at a GCE modified with a hydrophobic TF. The charge transfer rate found is slower than expected, probably because the ionic exchange at the TF-aqueous solution interface would delay the electron transfer process.