Preparation and voltammetric characterization of electrodes coated with Langmuir-Schaefer ultrathin films of Nafion®

Ultrathin films of Nafion(R) perfluorinated polymer were deposited on indium-tin oxide electrodes (ITO) by using Langmuir-Schaefer (LS) technique, after optimization of the subphase composition conditions. Morphological characteristics of these coatings were obtained by Atomic Force Microscopy (AFM). Nafion(R) LS films showed a good uniformity and complete coverage of the electrode surface, however a different organization degree of the polymer layer was evidenced with respect to thin films deposited by spin-coating. ITO electrodes modified with Nafion(R) LS coatings preconcentrate by ion-exchange electroactive cations, such as Ru[(NH3)(6)](3+), dissolved in diluted solutions. The electroactive species is retained by the Nafion(R) LS coated ITO also after transfer of the modified electrode into pure supporting electrolyte. This allowed the use of the ruthenium complex as voltammetric probe to test diffusion phenomena within the Nafion(R) LS films. Apparent diffusion coefficients (D-app) of Ru[(NH3)(6)](3+) incorporated in Nafion(R) LS films were obtained by voltammetric measurements. D-app values decrease slightly by increasing the amount of ruthenium complex incorporated in the ultrathin film. They are significantly lower than values typical for recasted Nafion(R) films, in agreement with the highly condensed nature of the Nafion(R) LS fims.