The Performance of Bipolar Membranes

Bipolar membranes are usually characterized in terms of their water dissociation capability, their resistance

Table 1 Electrochemical properties of the cation- and anion-selective layers of a bipolar membrane prepared by the technique described above

Anion exchange layer

Cation exchange layer

Ion exchange capacity

1.2

1.0

(mmol g"1)

Membrane thickness

60

60

fam)

Area resistance

1.05

1.31

(H cm2)

Permselectivity (%)

97.5

98.5

Swelling (%)

8

12.5

and their long-term stability. The water dissociation rate and electrical resistance of a membrane prepared by the procedure described above is shown in Figure 3A. Here the current density is shown as a function of the potential drop across the membrane. The test solutions in both compartments adjacent to the bipolar membrane are 1 molar Na2SO4. The results indicate that the current density is extremely low at potential differences of less than ca. 0.8 V. Then the current density increases up to 0.250 A cm~2 with very little increase in voltage drop. When this value is exceeded, the resistance of the membrane increases drastically, due to limitations in the water transport into the interphase region.

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