Conductive and capacitive properties of the bipolar membrane junction studied by AC impedance spectroscopy

The complete ac impedance spectrum of four bipolar membranes is analyzed bo th theoretically and experimentally taking into account both ionic transpor t and water dissociation together with the structural aspects of the bipola r junction. A theoretical model based on the Nernst-Planck and Poisson equa tions for the conductive and capacitive properties of the junction provides a qualitative description of the bipolar membranes for a broad range of el ectric currents and temperatures. Special attention is paid to the characte ristics of the bipolar junction structure and the contact region between th e two ion-exchange layers. It is observed that the effective area of this r egion increases with the electric current as mobile carriers are extracted from the interface and the layers come in closer contact.