Membranes perfluoro ionomer

Table II. Comparison of Monolayer and Multilayer Perfluoro Ionomer Membranes.

Table III. Mechanical Properties of Perfluoro Ionomer Membrane. (Ion Exchange Capacity 0.03 meq/g Dry Resin).

Table IV. Elongation of Perfluoro Ionomer Membrane Reinforced with PTFE Fabric.

The optimum current density of the membrane process (including the SPE cell process) is higher than that of the diaphragm process, because of the relatively high cost of the perfluoro ionomer membrane and its greater sensitivity to impurities, which requires the use of more expensive material for equipment. 

Ames RL, Way D, Bluhm EA. 2005. Dehydration of nitric acid using perfluoro carboxylate ionomer membranes. J. Membr. Sci. 249 65-73. 

Low cost (final target for electric vehicle apphcations would be cheaper than US 10/m ) need to be taken into account. While a number of PEMs have been developed, no single membranes fulfill aU of these requirements. Currently, the most promising PEMs are perfluoro sulfonic acid (PFSA) ionomers. Another candidate second to the PFSA ionomers is non-fluorinated (or in some cases only slightly fluorinated) hydrocarbon ionomers. The aim of this chapter is to review the most recent progress on these two classes of ionomer membranes for low-temperature fuel cell applications... 

One of the significant differences between hydrocarbon ionomers and perfluoro-sulfonic acid polymers is add groups. The pKa value of benzenesulfonic acid (PhSOsH) is 2.5 and that of trifluoromethanesulfonic acid (CF3SO3H) is —13. The pKa value was estimated to be ca. 1 for sulfonated polyether ketone and ca. —6 for Nafion membranes [78]. Therefore, the effective proton concentration and proton mobility should be lower in the hydrocarbon ionomer membranes. Without appropriate molecular design such as multiblock copolymer and sulfonic acid clusters as mentioned above, hydrocarbon ionomer membranes lack well-developed ionic channels due to less pronounced hydrophilic and hydrophobic phase separation, which causes the lower proton conductivity at low humidity. 

Several groups have found that counterions have a great effect on the thermal stability of perfluoro-sulfonated ionomer membranes (Feldheim et al, 1993 Lage et al., 2004a,b Bas et al., 2009). Using TG analysis, Feldheim et al. (1993) found the thermal stability of Nafion perfluorosulfonated ionomer to be... 

FIG U RE 2.2 Chemical structures of perfluorinated ionomers with sulfonic acid (la = Nafion, Flemion lb = Aciplex 2a = Dow, Hyflon Ion 2b = 3M 2c = Asahi Kasei 3 = Asahi Glass) and bis[(perfluoro)alkyl sulfonyl] groups (4). (Reprinted with permission from Peckham, T. J., Yang, Y, and Holdcroft, S. et al., Proton Exchange Membrane Fuel Cells Materials, Properties and Performance, Wilkinson, D. P. et al., Eds., Figure 3.16, 138, 2010, CRC Press, Boca Raton. Copyright (2010) CRC Press.)... 

Furthermore, PAN hollow fiber carbon membranes were coated with zeohtes [28], PI [29] and perfluoro-srrlfonated ionomer (PSI) [30] to produce composite membranes. After this period, there was not much research involving the rrse of PAN as a precursor for carbon membranes until late 2003, when Davis and Ismail [31] prepared their carbon hollow fiber membrane from PAN precursor. 

Linkov VM, Bobrova LP, Timofeev SV, Sanderson RD (1995) Composites membranes from perfluoro-sulfonated ionomer on carbon and ceramic supports. Mater Lett 24 (1-3) 147-151 David LIB, Ismail AF (2003) Influence of the thermostabilization process and soak time during pyrolysis process on the polyacrylonitrile carbon membranes for OyN separation. J Membr Sci 213 (1-2) 285-291 Geiszler VC (1997) Polyimide precursors for carbon membranes. PhD Thesis, University of Texas at Austin, TX, USA... 

Nafion is an ionomer that has a hydrophobic tetrafluoroethylene (TFE) backbone and perfluoro alkyl ether (PFAE) side chains terminated with hydrophilic sulfonate salt [1 ], as shown in Fig. 1. It was introduced by DuPont in 1960 and has been used in a variety of applications such as an ion-selective membrane for the Qilor-Alkali process [5, 6], a water transport membrane for humidifiers, and as a strong acid catalyst [7]. Nafion was introduced as a polymer electrol34e membrane (PEM) in fuel cells in the early 1990s [4, 8]. Compared to hydrocarbon membranes, Nafion was chemically more robust in the fuel cell and the acid form has high proton conductivity. There have been many efforts to find alternative membrane materials... 

Eisman, G. A., The physical and mechanical properties of a new perfluoro-sulfonic acid ionomer for use as a separator/membrane in proton exchange... 

Moore, R.B. and Martin, C.R. (1986) Procedures for preparing solution-cast perfluoro-sulfonate ionomer films and membranes. Anal. Chem., 58, 2569-2570. 

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