Theoretical and experimental study of current-voltage characteristics of asymmetric bipolar membranes

A mathematical model describing the transfer of hydrogen and hydroxyl ions and ions of salt through asymmetric bipolar membranes is developed. The model accounts for an electrochemical reaction, which is water splitting at the boundary between an anion-exchange and a cation-exchange layers. The chemical reaction causes the occurrence of the overvoltage of the bipolar region, which leads to a deviation of the current-voltage characteristics of the bipolar membrane from linearity. We have demonstrated bifunctionality of the asymmetric bipolar membranes, their ability to transport ions of salt and water dissociation products simultaneously, both experimentally and theoretically. Depending on their structure and the external conditions, the first or the second function may be dominant. In dilute solutions, water dissociation occurs with high current efficiency, and in the concentrated solutions, there is a simultaneous transfer of salt ions, as well as water splitting products.