Membrane perfluorinated

Ionomer membranes are used in fuel cells in order to separate the anode and cathode compartment and to allow the transport of protons from the anode to the cathode. The typical membrane is Nation , which consists of a perfluorinated backbone and side chains terminated by sulfonic groups. In the oxidizing environment of fuel cells, Nation , as well as other membranes, is attacked by reactive oxygen radicals, which reduce the membrane stability. Direct ESR was used recently in our laboratory to detect and identify oxygen radicals as well as radical intermediates formed in perfluorinated membranes upon exposure to oxygen radicals [73,74]. The three methods used to produce oxygen radicals in the laboratory and the corresponding main reactions are shown below. 

Commercially available perfluorinated membranes are summarized in Table 7. 

Peet, D.L. Austin, J.H. (1986) Nafion perfluorinated membranes operation in chlor-alkali plants. 

One breakthrough occurred in membrane technology when PolyFuel, in Mountain View, CA, produced a hydrocarbon polymer membrane with improved performance and lower costs than the current perfluorinated membranes. This cellophane like film has performed better than more common perfluorinated membranes, such as DuPoint s Nation material. 

In a PEMFC, the power density and efficiency are limited by three major factors (1) the ohmic overpotential mainly due to the membrane resistance, (2) the activation overpotential due to slow oxygen reduchon reaction at the electrode/membrane interface, and (3) the concentration overpotential due to mass-transport limitations of oxygen to the electrode surfaced Studies of the solubility and concentration of oxygen in different perfluorinated membrane materials show that the oxygen solubility is enhanced in the fluorocarbon (hydrophobic)-rich zones and hence increases with the hydrophobicity of the membrane. The diffusion coefficient is directly related to the water content of the membrane and is thereby enhanced in membranes containing high water content the result indicates that the aqueous phase is predominantly involved in the diffusion pathway. ... 

Gierke, T. D., Munn, G. E. and Wilson, F. C. 1981. The morphology in Nafion perfluorinated membrane products, as determined by wide-angle and small-angle x-ray studies. Journal of Polymer Science Polymer Physics 19 1687-1704. 

Dolye, M. and Rajendran, G. 2003. Perfluorinated membranes. In Handbook of fuel cells—Fundamentals, technology and applications, part 3, ed. W. Vielstich, A. Lamm and H. A. Gasteiger, 351. Colchester, England John Wiley Sons. 

Bosnjakovic, A. and Schlick, S. 2004. Nafion perfluorinated membranes treated in Fenton media Radical species detected by EPR spectroscopy. Journal of Physical Chemistry 108 4332-4337. 

Eisman, G. A. 1990. The applications of Dow GhemicaTs perfluorinated membranes in proton exchange membrane fuel cells. Journal of Power Sources 29 389-398. 

S. Tsushima, S. Hirai, K. Kitamura, M. Yamashita, S. Takasel, MRI application for clarifying fuel cell performance with variation of polymer electrolyte membranes Comparison of water content of a hydrocarbon membrane and a perfluorinated membrane. Appl. Magn. Reson. 32, 233-241 (2007)... 

Bosnjakovic A, Schlick S (2004) Nation perfluorinated membranes treated in Fenton media radical species detected by ESR spectroscopy. J Phys Chem B 108(14) 4332—7... 

Perfluorinated membranes are still regarded as the best in the class for PEM fuel cell applications. - These materials are commercially available in various forms from companies such as DuPont, Asahi Glass, Asahi Chemical, 3M, Gore, and Sol-vay. Perfluorosulfonic acid (PFSA) polymers all consist of a perfluorocarbon backbone that has side chains terminated with sulfonated groups. 

Doyle, M. and Rajendran, G., Perfluorinated membranes, in Elandbook of Fuel Cells Fundamentals, Technology, and Applications, 1st ed., Vielstich, W., Lamm, A., and Gasteiger, H.A., Eds., John Wiley Sons, West Sussex, England, 2003, p. 351. 

In addition, BPM must have an experimental potential to achieve the water-splitting capability as close as possible as the theoretical value equals 0.83 V at 25°C. Nowadays, superior styrene-divinylbenzene copolymer membranes can be easily purchased, perfluorinated membranes with great chemical stability are on the market, and BPM with an industrial-scale lifetime (>10,000 h) is available. 

Industrial production of perfluorinated ionomers, Nafion membranes, and all perfluorinated membranes is costly due to several factors first, the monomers used are expensive to manufacture, since the synthesis requires a large number of steps and the monomers are dangerous to handle. The precautions for safe handling are considerable and costly. Secondly, the PSEPVE monomer is not used for other applications, which limits the volume of production. The most significant cost driver is the scale of production. Today, the volume of the Nafion market for chlor-aUcali electrolysis (150,000 m year ) and fuel cells (150,000 m year ) is about 300,000 m year resulting in a production capacity of 65,000 kg year. When compared to large-scale production of polymers like Nylon (1.2 x 10 m year ), the perfluorinated ionomer membrane is a specialty polymer produced in small volumes. 

Nafion-perfluorinated membranes are manufactured from copolymers of tetrafluoroethylene and perfluorinated monomers and contain sulfonic groups on one side and carboxylic acid groups on the other. The membranes, originally designed for use in... 

Brochure DuPont Nation perfluorinated membranes, DuPont, Fayetteville, 1994. 

In spite of the documented, relatively high chemical stability of poly(PFSA) membranes in the fuel-cell environment, recent extensive work looking into the origins of performance loss observed in PEFCs has revealed important mechanisms of degradation that apply to perfluorinated membranes (while being further amplified in nonperfluorinated membranes). An important mechanism of membrane... 

Perfluorlnated ion-exchange membranes are derived from copolymers of tetrafluoroethylene (TFE) and a perfluorovinyl ether terminated by a sulfonyl fluoride group. The precursor of the perfluorinated membrane has the form... 

Ltd.) and the perfluorinated membranes produced by the Asahi Chemical Industry Company (18). Recently, carboxylate perfluorinated materials have been available from DuPont Company. 

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