BIPOLAR MEMBRANES UNDER FORWARD AND REVERSE BIAS CONDITIONS - THEORY VS EXPERIMENT

Bipolar membranes are layered structures composed of one cation-and on e anion-exchange membrane joined together in series. The current-volta ge curves of two recently developed bipolar membranes have been analys ed theoretically and experimentally under both forward and reverse bia s conditions. The experimental trends observed are high conductivity u nder forward bias conditions and high impedance first, and then electr ic field enhanced (EFE) water dissociation for high enough applied vol tages, under reverse bias conditions. The forward bias measurements ca n contribute to a better knowledge of some of the transport parameters entering also in the reverse biased membrane. Comparison of experimen t with a theory based on the Nernst-Planck and Poisson equations allow s for further testing of the theoretical model successfully employed p reviously for the case of the reverse biased membrane, and gives new s upport to the hypothesis that an EFE water dissociation reaction invol ving the membrane fixed groups in the bipolar junction is responsible for the breakdown of the current saturation regime observed under reve rse bias conditions.