Sulfonic acid membrane current efficiency

The strong acidity and high hydrophilicity of the perfluoro-sulfonic acid group result in a membrane of high water content and low electric resistance. Since the fixed-ion concentration in the sulfonic acid membrane is also low, current efficiency is less than 80% with caustic concentrations of 17% or more (26). The chemical stability of perfluorosulfonic acid group is excellent. Because of its low pKa value, the membrane can be exposed to solutions of pH 1. 

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).

Figure 5.2 compares the change in PNaCa of a phosphonic acid membrane and that of a sulfonic acid membrane with the concentration of the mixed salt solution when 1 1 mixed salt solutions composed of calcium chloride and sodium chloride of various concentrations were electrodialyzed.26 PNaCa of the phosphonic acid membrane is lower than that of the sulfonic acid membrane. Transport numbers of all alkaline earth metal cations relative to sodium ions for the phosphonic acid membrane are also lower than those of the sulfonic acid membrane.26 However, the current efficiency of the phosphonic acid membrane was about 10% lower than that of the sulfonic acid membrane. Alkaline earth metal cations more... 

Figure 3.15 Transport number of hydrogen ions relative to sodium ions (PNaH) and current efficiency of cations to the composition of an amphoteric ion exchange membrane. (O, ) quarternized membranes (N-methyl pyridinium and sulfonic acid groups) (A, A) tertiary amino groups membrane (pyridinium hydrochloride and sulfonic acid groups) (, A) PNa 11 (O, A) current efficiency (%). Electrodialysis was carried out at a current density of 20 mA cm 2 using a mixed solution of 0.25 N sodium chloride and 0.25 N hydrochloric acid for 60 min at 25.0 °C.

Fe(CN)6]3-.332 Another case to obtain quinone and hydroquinone by electrochemical oxidation of benzene with a high current efficiency, an anode modified by a bipolar ion exchange membrane, composed of a protonated poly-4-vinylpyridine layer and a perfluorocarbon sulfonic acid layer, is used. [Fe(CN)6]3 is incorporated in the inner layer (protonated poly-4-vinylpyridine) and is not contained in the solution. Release of [Fe(CN)6]3 from the inner layer is prevented by the outer layer. As a result, redox catalysts, i.e., Cr6+/Cr3+, or [Fe(CN)6]4-/ [Fe(CN)6]3 incorporated in the bipolar ion exchange membrane on the electrode surface accomplish catalysis more efficiently than if they were dissolved in the electrolyte solution.333... 

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