The low frequency conductance of bipolar membranes demonstrates the presence of a depletion layer

The electrical conductance of a 2-sheet bipolar membrane was measured as a function of frequency over the range 0.1 Hz–10 kHz in electrolyte solutions containing 1, 10 and 100 mM KCl. The 2-sheet bipolar membrane was also separated into its monopolar regions and their electrical properties were examined individually. The low frequency conductance of the bipolar membrane was always significantly less than the value which would have been obtained if the monopolar regions were too far apart to interact. The data suggest that the separation of the ion exchange regions was approximately ≤1 nm, even in the absence of a large DC current.