Perfluorocarboxylic acid membrane current efficiency

Influence of Electrolysis Conditions. Among the various electrolysis conditions, brine purity has the most significant effect on the life of the membranes. The presence of a small amount of multivalent cations leads to formation of metal hydroxide deposits in the membrane, and thus causes a decrease in current efficiency, an increase in cell voltage, and damage to the polymer structure of the membrane. With perfluorocarboxylic acid membrane, the presence of more than 1 ppm of calcium ion will begin to cause these problems in a very short period (1 - 8). To obtain stable current efficiency and cell voltage, it is therefore essential to establish effective brine purification methods. 

The typical perfluorocarboxylic acid membrane developed by Asahi Chemical is a multilayer membrane prepared by chemical treatment. The structure of the membrane is optimized for high current efficiency and low electric resistance. The thickness of the carboxylic acid layer is in the range of 2 to 10 microns. The chemical structure of the membrane is as follows (72). 

The weak acidity and relatively low hydrophilicity of the perfluorocarboxylic acid group results in a very high current efficiency of over 96%, although its electric resistance is high (1, 3, 5, T y 10, 26-29). The membrane can be exposed to fairly acidic solution as the pKa value is around 2. Its chemical stability is quite good under electrolysis conditions. 

Figure 2. The thickness of CO OH layer, current efficiency, and electric resistance of a multilayer perfluorocarboxylic and sulfonic acid membrane prepared by chemical treatment (COOH/SOsH).

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