Perfluorosulfonates

The first membranes to show significant potential and trigger the development of membrane electroly2ers were made from the perfluorosulfonate polymer called Nafion (40,41). 

Membrane cells are the state of the art chlor-alkah technology as of this writing. There are about 14 different membrane cell designs in use worldwide (34). The operating characteristics of some membrane cells are given in Table 3. The membranes are perfluorosulfonate polymers, perfluorocarboxylate polymers, and combinations of these polymers. Membranes are usually reinforced with a Teflon fabric. Many improvements have been made in membrane cell designs to accommodate membranes in recent years (35,36). 

The electrolyte is a perfluorosulfonic acid ionomer, commercially available under the trade name of Nafion . It is in the form of a membrane about 0.17 mm (0.007 in) thick, and the electrodes are bonded directly onto the surface. The elec trodes contain veiy finely divided platinum or platinum alloys supported on carbon powder or fibers. The bipolar plates are made of graphite or metal. 

Note Nafion is Du Font s brand name for perfluorosulfonate polymers. 

The PEM (proton exchange membrane) material is a perfluorosulfonic acid polymer film. Several manufacturers make PEMs in one form or another. We used one made by du Pont called Nation 117. Nation 117 is a transparent polymer film about 175 microns (0.007 inches) thick. Dow Chemical Co., Asahi Chemical Co., and Chloride Engineers Ltd. make something similar. A patent describing how one PEM manufacturer s film is processed is listed in the references section at the end of this article. 

C.H. Liu, K.T. Liao, and H.J. Huang, Amperometric immunosensors based on protein A coupled poly-aniline-perfluorosulfonated ionomer composite electrodes. Anal. Chem. 72, 2925-2929 (2000). 

A.F. Chetcuti, D.K.Y. Wong, and M.C. Stuart, An indirect perfluorosulfonated ionomer-coated electrochemical immunosensor for the detection of the protein human chorionic gonadotrophin. Anal. Chem. 71, 4088-4094 (1999). 

A.A. Karyakin, E.A. Kotel nikova, L.V. Lukachova, E.E. Karyakina, and J. Wang, Optimal environment for glucose oxidase in perfluorosulfonated ionomer membranes improvement of first-generation biosensors. Anal. Chem. 74, 1597—1603 (2002). 

B. Limoges, C. Degrand, and P.J. Brassier, Redox cationic or procationic labeled drugs detected at a perfluorosulfonated ionomer film-coated electrode. J. Electroanal. Chem. 402, 175-187 (1996). 

Perfluoropropyl vinyl ether (PPVE), properties of, 18 330 Perfluorosulfonate ionomers, 14 475... 

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. 

As the state-of-the-art PEMFC electrodes are optimized for operation below 100 °C and the use of perfluorosulfonic acid as electrolyte, significant new R D will be needed when a new electrolyte emerges with high temperature operation as a consequence. 

K. S. Litwiler, P. M. Kluczynski, and F. V. Bright, Determination of the transduction mechanism for optical sensors based on rhodamine 6G impregnated perfluorosulfonate films using steady-state and frequency-domain fluorescence, Anal Chem. 63,797-802(1991). 

In 1973, Dupont began to commercialize their first perfluorosulfonic add cation exchange membrane, Nafion. Since then until now, Nafion has been attracting much attention because of its superb chemical and thermal stability, high ionic conductivity, excellent permselectivity and good mechanical strength. Many approaches have been proposed to use this unique material as a modifier of electrochemical electrode surfaces. 

The evaluation of catalysts typically uses two techniques. The first is evaluation as a thin layer on a bulk electrode (e.g., glassy carbon) in dilute liquid electrolyte (e.g., H2 4) either as a static electrode or an RDE. In the study of oxygen reduction, there has been much discussion as to the most appropriate electrolyte to use. In general, dilute perchloric acid (HCIOJ is preferred because of its noncoordinating nature, it is thus closest to the environment foxmd within a FEM catalyst layer with perfluorosulfonic acid ionomer. A possible alternative is trifluoromethylsulfonic acid (CF3SO3H), which mimics perfluorosulfonic acids closely, but there are relatively few studies with this acid. Rotating... 

Kim, Y. S., Dong, L., Hickner, M. A., Glass, T. E., Webb, V. and McGrath, J. E. 2003. State of water in disulfonated poly(arylene ether sulfone) copolymers and a perfluorosulfonic acid copolymer (Nafion) and its effect on physical and electrochemical properties. Macromolecules 36 6281-6285. 

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. 

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. 

Hoshi, N. and Ikeda, M. 2005. Perfluorosulfonic acid polymer. Japan Patent 2005048121. 

Savett, S. C., Atkins, J. R., Sides, G. R., Harris, J. L., Thomas, B. H., Greager, S. E., Pennington, W. T. and DesMarteau, D. D. 2002. A comparison of [(perfluoroalkyl) sulfonyl] imide ionomers and perfluorosulfonic acid ionics for applications in PEM fuel-cell technology. Journal of the Electrochemical Society 149 A1527-A1532. 

Landis, F A. and Moore, R. B. 2000. Blends of a perfluorosulfonate ionomer with poly(vinylidene fluoride) Effect of counterion type on phase separation and crystal morphology. Macromolecules 33 6031-6041. 

Mauritz, K. A., Stefanithis, I. D., Davis, S. V., Scheetz, R. W, Pope, R. K., Wilkes, G. L. and Huang, H. H. 1995. Microstructural evolution of a silicon-oxide phase in a perfluorosulfonic acid ionomer by an in situ sol-gel reaction. Journal of Applied Polymer Science 55 181-190. 

Adjemian, K. T., Srinivasan, S., Benzieger, J. and Bocarsly, A. B. 2002. Investigation of PEMFC operation above 100°C employing perfluorosulfonic acid silicon oxide composite membranes. Journal of Power Sources 109 356-364. 

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