Perfluorinated ionomer

The term chlor-alkali refers to those products obtained from the commercial electrolysis of aqueous sodium chloride. These are chlorine, sodium hydroxide, and sodium carbonate. The first two are produced simultaneously during the electrolysis while the latter is included because it is also produced in small quantities and shares many of the end uses of sodium hydroxide. Perfluorinated ionomer membranes are permeable to sodium ions but not the chloride ions, and hence they are useful for these electrolytic cells. The arrangement of a typical membrane cell is shown in Figure 10.2. 

Fujimura M., Hashimoto T., and Kawai H., Small-angle x-ray scattering study of perfluorinated ionomer membranes. 2. Models for ionic scattering maximum. Macromolecules, 15, 136, 1982. 

M. Seko, S. Ogawa, and K. Kimoto, in Perfluorinated Ionomer Membranes, ACS Symposium Series 180, American Chemical Society., Washington, D.C. (1982), pp. 365 110. 

Gebel, G. and Lambard, J. 1997. Small-angle scattering study of water-swollen perfluorinated ionomer membranes. Macromolecules 30 7914—7920. 

Atkins, J. R., Sides, C. R., Greager, S. E., Harris, J. L., Pennington, W. T., Thomas, B. H. and DesMarteau, D. D. 2003. Effect of equivalent weight on water sorption, PTFE-like crystallinity, and ionic conductivity in bis[(perfluoroalkyl) sulfonyl] imide perfluorinated ionomers. Journal of New Materials for Electrochemical Systems 6 9-15. 

Yang, J. C. and Kyu, T. 1990. Kinetics of phase separation of Nafion perfluorinated ionomer and poly(vinylidene fluoride) blends. Macromolecules 23 182-186. 

A lesser number of papers have appeared regarding the carboxylate version of Nafion, and the works of Yeager et al., - Seko et al., and Perusich et al. ° are of special note. Nafion-like carboxylate materials have also been reported." These similar materials will not be discussed here, as the exclusive emphasis is on the stronger-acid sulfonated versions because this critical review is within a collection of articles in which perfluorinated ionomers are considered within the context of fuel cells. 

The DuPont Nafion materials, both sulfonate and carboxylate varieties, are not entirely unique, as similar perfluorinated ionomers have been developed by others such as the Asahi Chemical Company (commercial name Aciplex) and the Asahi Glass Company (commercial name Flemion). The comonomer chemical structures of and further information on these materials are given in the recent review article by Doyle and Rajendvan. Now commercially unavailable, but once considered a viable alternative, the Dow Chemical Company developed a somewhat similar perfluorinated ionomer that resembled the sulfonate form of Nafion except that the side chain of the former is shorter and contains one ether oxygen, rather than two ether oxygens, that is, —O—... 

Other reviews of the literature on Nafion and similar perfluorinated ionomers have appeared over the years. The early book (1982) by Eisenberg and... 

Scheme 1. Structure of the perfluorinated ionomer membrane (Nafion ).

Other perfluorinated ionomer membranes, chemically very similar to Nafion, are also available commercially. Aciplex, manufactured by the Asahi Chemical Company, is very similar to Nafion, except that it has perfluoropropanesulfonic acid side chains. Flemion (Asahi Glass Company), in contrast, possesses perfluorobutanoic acid functions. 

A. Eisenberg, and H. L. Yeager (eds.), Perfluorinated Ionomer Membranes, The American Chemical Society, Washington, DC, 1982. 

Major areas of application are in the field of aqueous electrochemistry. The most important application for perfluorinated ionomers is as a membrane separator in chloralkali cells.86 They are also used in reclamation of heavy metals from plant effluents and in regeneration of the streams in the plating and metals industry.85 The resins containing sulfonic acid groups have been used as powerful acid catalysts.87 Perfluorinated ionomers are widely used in worldwide development efforts in the held of fuel cells mainly for automotive applications as PEFC (polymer electrolyte fuel cells).88-93 The subject of fluorinated ionomers is discussed in much more detail in Reference 85. 

Heitner-Wirguin, C. (1996). Recent advances in perfluorinated ionomer membranes Structure, properties and applications, J. Membrane Sci. 120, 1. 

Proton Exchange Membrane (PEMFC) These cells use a perfluorinated ionomer polymer membrane which passes protons from the anode and cathode. They operate at about 80 °C. These are being developed for use in transport applications and for portable and small fuel cells. 

DesMarteau, D.D., Novel perfluorinated ionomers and ionenes, J. Fluorine Chem., 72, 203, 1995. 

Mauritz, K.A., Organic-inorganic hybrid materials perfluorinated ionomers as sol-gel polymerization templates for inorganic alkoxides. Mater. Sci. Eng. C, 6, 121, 1998. 

Figure 3.43. Structure of Nafion-115 at ambient humidity derived from small-angle X-ray spectroscopy. The lighter areas are cluster structures in the material. (Reprinted with permission from J. Elliott, S. Hanna, A. Elliott, G. Cooley (2000). Interpretation of the small-angle X-ray scattering from swollen and oriented perfluorinated ionomer membranes, Macromolecules 33, 4161-4171. Copyright American Chemical Society.)...

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