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

The ideal cation permselectlvlty exhibited by electrode coatings prepared from the polyelectrolyte Nation leads to ejection of countercatlons from the coatings during electrochemical oxidation of Os(bpy)₃²⁺counterlons incorporated in the coatings. If the coatings are saturated with Os(bpy)₃²⁺so that these are the only counterlons present, one-third of the incorporated cations are ejected during the oxidation of Os(bpy)₃²⁺to Os(bpy)₃³⁺. The cyclic voltammetry of the incorporated Os(bpy)₃^3+/2+couple is altered substantially in the absence of additional counterlons. The changes are attributed to contributions to the voltammetrlc potentials from the free energy of transfer of these strongly bound counterlons. Mtcrotlp electrodes positioned just above Nafion-coated electrodes were used to monitor the ejection of both Os(bpy)₃³⁺and Os(bpy)₃²⁺from Nation coatings. Much more of the former complex is ejected from saturated coatings which is believed to be the result of electric field-assisted ejection.