Carboxylic acid layer, current efficiency

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). 

Fig. 17.7 Influence of Na+ concentration at interface of sulphonic acid and carboxylic layers on current efficiency 3-4 N NaCI 1.0-5.5 kA rrT2 33% NaOH.

Dziewinski et al. [71] have reported current efficiencies greater than 90% at 80°C for isopropanol, acetone, and acetic acid, whereas methanol, chloroform, and carbon tetrachloride were converted into carbon dioxide at room temperature with ca. 100% current efficiency. The predicted order of ease of oxidation is alcohols < aldehydes, ketones < carboxylic acids. Thus, the complete conversion to carbon dioxide, in particular for large organic molecules, is expected only at elevated temperatures. To avoid the use of a separator, Farmer et al. [72,75] employed C0SO4 in sulfuric acid. A scheme of the system is shown in Fig. 17. Both electrodes, the anode and the cathode, are usually of a Pt-containing surface layer, although other materials such as Au, steel, graphite, Ti, Nb, Ir, or tin oxide can also be used. H2 is evolved at the cathode because the deposition of the mediator takes place... 

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