THE INFLUENCE OF HETEROGENEITY OF BIPOLAR MEMBRANES ON THEIR CURRENT-VOLTAGE CURVES

A structure is suggested for unipolar parts of heterogeneous bipolar m embranes (BPM). The structure is a two-phase system that consists of a nonconducting phase (thermoplastic polymeric binder) permeated with n oninteracting ion-conducting channels. A heterogeneous H-OH junction o f the membranes is considered. Its true generating (conducting) area i s represented as a total overlapping area of cationite and anionite ch annels in the region of the bipolar junction. The model suggested for the junction is used to derive an equation that connects the effective generating area of the H-OH junction with the electroconductivity of unipolar parts of BPM, the tortuosity factor of the channels, and the electroconductivity of pure ionites constituting the membranes. The eq uation is used to calculate current-voltage curves for an MB-2 membran e with different electro-conductivity of unipolar layers, which are in satisfactory agreement with the experimental curves. It is shown that increasing the fraction of the polymeric binder in unipolar parts of the MB-2 membrane from 30 to 70 wt % makes the density of the current responsible for generating the H+ and OH- ions drop approximately a hu ndred-fold at identical voltages across BPM. This is attributed to a d ecrease in the effective generating area of membranes. It is demonstra ted that the presence of a polymeric binder in membranes affects neith er the shape of the current-voltage curves nor the mechanism of genera ting ions in BPM. The current-voltage curve for the H-OH junction of a n MB-2 membrane free of polymeric binder is calculated.