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

Ultrathin films of Nafion 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 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 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 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 LS films. Apparent diffusion coefficients (Dapp) of Ru[(NH3)6]3+ incorporated in Nafion LS films were obtained by voltammetric measurements. Dapp 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 films, in agreement with the highly condensed nature of the Nafion LS fims.