Acid membranes

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... 

Fig. 1.16 Schematic representation of the nanofibrous poly (acrylonitrile-co-acrylic acid) membrane containing MWCNTs, as well as the promoted electron transfer from hydrogen peroxide to the immobilized catalase through the PANCAA/MWCNTs nanofiber. Reprinted from [209] (reproduced by permission ofWiley-VCH).

Electrolysis of water contained within a perfluorinated sulphonic acid membrane (Membrel water electrolysis) developed by ABB [133,201-205] and Sasakura [200]. Current efficiencies reach 14-15% at current densities of 10000 A m2 and more. The cells are generally immersed directly in the water so that ozone is introduced directly into the water to be treated, Fig. 18. 

High Temperature Operation of the PEMFC The first generation of commercial PEMFCs will use presently known components, consisting of a perfluorosulfonic acid membrane as electrolyte and catalyst compositions as cited above. The electrolyte determines that the fuel cell needs to be operated at fully humidified conditions and limits the operating temperature to 80-90 °C. 

A. M. Kleinfeld and M. F. Lukacovic, Energy-transfer study of cytochrome b5 using the anthroyloxy fatty acid membrane probes, Biochemistry 24, 1883-1890 (1985). 

D. B. Chalpin and A. M. Kleinfeld, Interaction of fluorescence quenchers with the -(9-anthroyloxy) fatty acid membrane probes, Biochim. Biophys. Acta 731, 465 174 (1983). 

Demel, R.A., Jordi, W., Lambrechts, H., van Damme, H., Hovius, R. and de Kruijff, B., 1989, Differential interactions of apo- and holocytochrome c with acidic membrane lipids in model systems and the implication for their import into mitochondria, /. Biol. Chem. 264 3988-3997. 

Geiger, A. B., Newman, J. and Prausnitz, J. M. 2001. Phase equilibria for water-methanol mixtures in perfluorosulfonic-acid membranes. AlChE Journal 47 445-452. 

Ren, X. and Gottesfeld, S. 2001. Electro-osmotic drag of water in poly(perfluorosulfonic acid) membranes. Journal of the Electrochemical Society 148 A87-A93. 

Patri, M., Hande, V. R., Phadnis, S. and Deb, P. C. 2004. Radiation-grafted solid polymer electrolyte membrane thermal and mechanical properties of sulfonated fluormated ethylene propylene copolymer (FEP)-graft-acrylic acid membranes. Polymers for Advanced Technologies 15 622-627. 

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. 

Paddison, S. J. and Elliott, J. A. 2006. On the consequences of side chain flexibility and backbone conformation on hydration and proton dissociation in perfluorosulfonic acid membranes. Physical Chemistry Chemical Physics 8 2193-2203. 

Horsfall, J. A. and Lovell, K. V. 2001. Euel cell performance of radiation-grafted sulphonic acid membranes. Fuel Cells 1 186-191. 

Various membrane materials are to be compared for corrosion resistance in hydrochloric acid. Membrane samples are ultrasonically cleaned with Freon for 5 minutes and dried at 200°C for 2 hours followed by similar steps of ultrasonic cleaning with demineralized water and drying. The conditioned membrane samples are then immersed in 35% HG solution, making sure that no air bubbles are trapped in pores. The acid exposure at the test temperature (e.g. 25°C) continues for a given period (e.g. one week). The tested samples are ultrasonically washed with demineralized water for 5 minutes and dried at 200°C for 2 hours. The weights of the cleaned membrane samples before and after the acid exposure are compared to assess the relative corrosion resistance of various membrane materials. 

Futerko and Hsing presented a thermodynamic model for water vapor uptake in perfluorosulfonic acid membranes.The following expression was used for the membrane—internal water activity, a, which was borrowed from the standard Flory—Huggins theory of concentrated polymer solutions ... 

Nafion and Other Poly(perfluorosulfonic acid) Membranes 4590... 

All of these polyperfluorosulfonic acid membranes are expensive and suffer from the same shortcomings as Nation, namely low conductivity at low water contents, relatively low mechanical strength at higher temperature, and moderate glass transition temperatures. 

The conclusion is that membranous vesicles readily form a variety of amphiphilic molecules that would have been available in the early Earth environment, along with hundreds of other organic species. It is likely that during the chemical evolution leading to the first catalytic and replicating molecules, the ancestors of today s proteins and nucleic acids, membranous vesicles were available in the prebiotic environment, and ready to provide a home for the first forms of cellular life. 

Spychalla, J. P., Desborough, S. L. (1990). Fatty acids, membrane permeability, and sugars of stored potato tubers. Plant Physiol., 94, 1207-1213. 

Sowokinos, J. R., Orr, P. H., Knoper, J. A., Yarns, J. L. (1987). Influence of potato storage and handling stress, sugars, chip quality and integrity of the starch (amyloplast) membrane. Am. Potato J., 64,213-225. Spychalla,N. R, Desborough, S. L. (1990). Fatty acids, membrane permeability, and sugars of stored potato tubers. Plant Physiol., 94, 1207-1213. 

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. 

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