MASS-TRANSPORT STUDY OF NAFION(R) COATINGS SATURATED WITH [OS(BPY)(3)](2+) BY AN ELECTROCHEMICAL QUARTZ-CRYSTAL MICROBALANCE

Abstract

Ion transport out of and into the Nafion(R) coating on an electrode during the electrochemical processes was studied using an electrochemical quartz crystal microbalance (EQCM). After saturated loading of [Os(bpy)(3)](2+), the first cyclic voltammogram (CV) initiated from the lower limit showed an anodic peak around 0.85 V vs. Ag\AgCl which, according to a previous study by Anson's group, corresponds to ejection of the [Os(bpy)(3)](3+) complex from the Nafion(R) coating. However, the frequency change-potential (Delta f-E) curve obtained by EQCM showed an increase in the mass on the first positive scan. These contradictory results can be explained by the movement of water molecules in a direction opposite to that of [Os(bpy)(3)](3+) complexes. After a number of successive cycles, a steady state voltammogram was obtained. In this case the mass change was attributed mainly to the movement of the hydrated electroinactive counter-cations of the supporting electrolyte. The hydration numbers for two of the supporting electrolyte cations are in good agreement with the published results.