Sulfonic acid membrane

This article focuses on the commercial, ethylene-based ionomers and includes information on industrial uses and manufacture. The fluorinated polymers used as membranes are frequently included in ionomer reviews. Owing to the high concentration of polar groups, these polymers are generally not melt processible and are specially designed for specific membrane uses (see Fluorine compounds, organic—perfluoroalkane sulfonic acids Membrane technology). 

Apart from the problems of low electrocatalytic activity of the methanol electrode and poisoning of the electrocatalyst by adsorbed intermediates, an overwhelming problem is the migration of the methanol from the anode to the cathode via the proton-conducting membrane. The perfluoro-sulfonic acid membrane contains about 30% of water by weight, which is essential for achieving the desired conductivity. The proton conduction occurs by a mechanism (proton hopping process) similar to what occurs... 

Yu, J., Yi, B., Xing, D., Liu, R, Shao, Z. and Fu, Y. 2003. Degradation mechanism of polystyrene sulfonic acid membrane and application of its composite membranes in fuel cells. Physical Chemistry Chemical Physics 5 611-615. 

T. R. E. Kressman (69) performed similar tests at a homogeneous gel membrane of the phenol sulfonic acid type and KC1 solutions. In the range of a+= 10-3-3 and += 0.1 the slope was found to be approx, equal to the theoretical slope, which corresponds with a potential change of 58 mV at a change in activity with a factor of 10. U. Schindewolf and K. F. Bonhoeffer (141), who likewise investigated a phenol sulfonic acid membrane, found results analogous to those of Kressman. 

Short Side Chain Perfluorinated Sulfonic Acid Membranes.782... 

FCs must cost around 45/kW to be competitive with the internal combustion engine. Perfluorinated sulfonic acid membranes currently cost 100-200/KW resulting in PEM FC prices estimated to be of the order of 1000/KW. 

The development of new polymeric materials for polymer electrolyte fuel cell is one of the most active research areas, aiming at the new energy sources for electric cars and other devices. The mainstream of the material research for fuel cell is perfluoroalkyl sulfonic acid membranes such as Nafion, Acipex, and Flemion. The most well-known one is Nafion of Du Pont, which is derived from copolymers of tetrafluoro-ethylene and perfluorovinyl ether terminated by a sulfonic acid group.Protons, when dissociated from the sulfonic acid groups in aqueous environment, become mobile and the membrane becomes a proton conducting electrolyte membrane. 

Such ionic clusters have been studied in ionomers such as Naflon poly(perfluoropropylene oxide sulfonic acid) membranes clusters in ionomers have been reviewed recently by Mauritz and Hopfinger ( 7). These reviewers also quote a model for hydrated Naflon proposed by T. D. Gierke at the October, 1977, meeting of the Electrochemical Society, Atlanta, Georgia, in which aqueous spher-... 

Figure 5 shows the electrolyte uptake of the sulfonic acid membrane as a function of electrolyte concentration for three different acid electrolytes. The electrolyte content of the membrane decreases with increasing acid concentration. As shown in Table 2, both sulfonate and carboxylate membranes sorb large amounts of other solvents as well, particularly alcohols and other protic solvents. "" " ... 

The perfluorinated sulfonic acid membrane exhibits a very strong acidic behavior in water. As shown in Figure 6, the concentration of fixed ion for Nafion of 1200 EW in E-form is equivalent to 13 wt % sulfuric acid. A similar value of 10 wt % sulfuric acid was observed by LaConti et The value is a good indication of the acidity of a material. A recent study has reported that " the... 

Figure 4. Ionic clusters formed in perfluorinated sulfonic acid membrane.

Effect of Neutralization. Figure 6 shows the solvent uptake for Nafion in both H and Li form (5). It is clear that the swelling behavior of Nafion in Li form is rather similar to that of the un-neutralized sample. The magnitude of the swelling envelope II decreases as the membrane is converted to Li form. In contrast to this, the swelling peak at low < i of the radiation-grafted sulfonic acid membranes disappears upon neutralization (5). Yeo, et al, have proposed that the disappearance of the dual solubility parameter is related to the decrease of the organic character of the material. 

Figure 1. WAXD profiles for a series of the sulfonic acid membranes under dry state. The measured profiles are shown by dots, while Curves b-d are the decomposed profiles by the least squares method, and the Curve a is reconstructed from...

Figure 2. Temperature dependence of the WAXD profiles for the sulfonic acid membranes having 1500 EW.

Figure 3. Effect of annealing of the sulfonic acid membranes having 1500 EW the membranes as received (a), and the membranes annealed at 275° C (b).

Figure 9. SAXS at large s (the ionic scattering maximum) for the sulfonic acid membranes under dry state (a) and swollen state (b) as a function of EW.

Figure 11. Degradation rates of perfiuorinated sulfonic acid membranes.

After intensive research and development work, Asahi Chemical filed the basic patents of fluorinated carboxylic acid membrane and carboxylic and sulfonic acid membrane and the related electrolysis processes in 1974 (1 - 8). 

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).

Multilayer perfluorocarboxylic and sulfonic acid membrane by lamination or coating y... 

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