Bipolar polymeric arrangements on electrodes

Various theoretical and experimental aspects of ionomeric bipolar polymer films on electrodes are presented. Theoretical expressions estimating the rate of leakage of electroactive counterions incorporated in the inner layer predict a possible reduction of several orders of magnitude in the rate relative to single ion-exchange layers. These expectations are well met by experimental results for electroactive anions (Fe(CN)₆^3- in poly(xylylviologen)) as well as cations (Fe²⁺ in Nafion). In both cases a substantial long-term stabilization is obtained for the bipolar arrangements, in qualitative agreement with theory. It is also shown that the application of the outer polymer layer enables the use of soluble ion-exchange polymers for electrode surface modification.