Enhanced rate of the redox reaction of indigodisulfonate at electrodes coated with poly[1-methyl-3-(pyrrol-1-ylmethyl)pyridiniun]chloride films

In order to answer the question of why poly[1-methyl-3-(pyrrol-1-ylmethyl)pyridinium]chloride films markedly increase the voltammetric current of indigodisulfonate (IS) ions, the authors have examined the impedance response of IS-loaded film electrodes at different oxidation levels and thicknesses of the loaded film. The standard heterogeneous rate constant at the modified electrodes is approximately three orders of magnitude lower than that at a bare electrode, because of the strong binding force of the redox anion to the polycationic film. Electron transport in the loaded film is appropriately described as a diffusion-like process due to intermolecular electron hopping. The diffusion coefficients of charge carriers suggest that electrons move much more slowly through the film than ions. In conclusion, the electrocatalytic effect produced by the polymer film is attributed to an effective extraction of IS from very dilute solutions (the partition coefficient is 2 x 10(5)). (C) 1998 Elsevier Science S.A. All rights reserved.