Use of Electrochemical Microscopy to Examine Counterion Ejection from Nafion Coatings on Electrodes

Abstract

The ideal cation permselectivity exhibited by electrode coatings prepared from the polyelectrolyte Nafion leads to ejection of countercatlons from the coatings during electrochemical oxidation of Os(bpy)_3^(2+) counterions incorporated in the coatings. If the coatings are saturated with Os(bpy)_3^(2+) so that these are the only counterions present, one-third of the incorporated cations are ejected during the oxidation of Os(bpy)_3^(2+) to Os(bpy)_3^(3+). The cyclic voltammetry of the incorporated Os(bpy)_3^(3+/2+) couple is altered substantially in the absence of additional counterions. The changes are attributed to contributions to the voltammetric potentials from the free energy of transfer of these strongly bound counterions. Microtip electrodes positioned just above Nafion-coated electrodes were used to monitor the ejection of both Os(bpy)_3^(3+) and Os(bpy)_3^(2+) from Nafion coatings. Much more of the former complex lo ejected from saturated coatings which is believed to be the result of electric field-assisted ejection