バイポーラ膜の電気化学特性

抄録

In this work, bipolar membrane (BPM) was prepared and membrane characteristics were studied.
A novel bipolar membrane was prepared by forming polypyrrole from a pyrrole monomer in the presence of Fe³⁺ at the interface between commercial cation and anion exchange membranes.
In an electrodialytic cell composed of four compartments with BPM fixed in the central portion, the current-voltage curve was measured under constant current supply. The current-voltage relation indicated an Ohmic change against the positive current, while the relation abruptly increased the current against the negative current. The increased current seems to be attributable to the proton and hydroxyl ions that were produced inside the bipolar membrane. According to the equation introduced by Mafe et al., these phenomena were interpreted as being due to the increased rate constant of water dissociation in the bipolar membrane.
On the other hand, water splitting was also noticed because of pH changes in the KCl solution when dc current was supplied through a pair of Pt electrodes from the anion exchange layer to the cation exchange layer of BPM. When a reverse current (positive current) was applied to the same system, water splitting did not take place. Concentrations of protons or hydroxyl ions calculated from pH values changed linearly in relation to time and each flux was obtained from the slope of the relations. Furthermore, current efficiency was estimated as the ratio of flux to added current. It was indicated that the current efficiency is closely related to donnan salts in bipolar membrane.