Membrane potential of bipolar membranes

The membrane potential of a bipolar membrane composed of a cation-exchange layer in series with an anion-exchange layer is analyzed theoretically and experimentally. The theoretical approach is based on an extension of the Nernst-Planck equations of monopolar charged membranes to the case of the two ion-exchange layers in series and the diffusion boundary layers adjacent to the bipolar membrane. The experimental results concern the transient behavior, stirring effects and concentration dependence of the membrane potential, and can be explained by means of the above theoretical approach. It is shown that membrane potential measurements can contribute significantly to a better electrochemical characterization of bipolar membranes.