Nafion materials

Unfortunately Nafion materials have not found commercial application as catalysts because of their extremely high cost. There were several attempts to use supported catalysts made by applying of low-molecular-weight Nafion polymer from solutions onto inert supports. However, such catalysts could only be used in very few reactions between nonpolar reagents in other cases the surface catalytic layer was easily washed away from the surface. 

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—... 

The mechanical properties of Nafion materials have not been of the most critical importance, as in the case of commercial thermoplastics or composite materials that are expected to be load-bearing. Rather, the primary focus has been on transport properties. To be sure, the mechanical integrity of membranes as mounted in cells, and under the perturbation of pressure gradients, swelling-dehydration cycles, mechanical creep, extreme temperatures, and the onset of brittleness and tear resistance, is important and must be taken into consideration. 

Until recently, nearly all studies of perfluorlnated ionomers have been carried out with Nafion (110). Materials with shorter side chains were developed by Dow Chemical Co. in the early 198O s (111) and in a later chapter, Tant et. al, contrast the properties of the short side chain perfluorosulfonlc acid lonomers with those of a comparable Nafion material. 

Perfluorinated ionomers have reached a high level of industrial importance due to their outstanding performance as membranes in applications such as chior-alkali cells and fuel cells (1). The Nafion material synthesized by duPont more than twenty years ago... 

The lowest temperature 6 peak which was detected as a tall In the spectrum of the precursor, has disappeared both in the G" and the tan curves of the 90Z Nafion-Na. Also, this 6 peak was not observed in the dielectric studies of the Nafion acid (46), strongly indicating that the peak may be a unique feature to the precursor which is not encountered in the ion containing Nafion materials. This relaxation was identified previously with the motion of —SO2F groups. 

Partially Ionized Nafion-Na. Partially ionized samples were prepared by Kyu et al (58) by immersing the precursor samples in a lOZ NaOH solution at approximately Ib C for varying periods of time. The precursor is a hydrophobic material, therefore NaOH diffusion must be extremely slow initially with the conversion taking place primarily at the surface of the sample. Once the outermost layer is converted to the Nafion salt, the rate of water diffusion appears to be greatly enhanced, allowing the conversion of the inner layers into ionic Nafion material. The conversion is therefore expected to occur layer... 

Polymeric proton exchange membrane needs to be maintained properly humidified to guarantee a satisfactory ion conductivity during stack operation (see Sect. 3.2). In fact it exists a strong relationship between proton conductivity and water content of Nafion material used as membrane in PEMFC [24, 25]. Unfortunately the water produced at cathode side and the air moisture could be not sufficient to maintain properly wet the membranes in all working conditions, because of complex phenomena involving water within MEA [26] (Fig. 4.7). 

One recent breakthrough in membrane technology occurred when PolyFuel, in Mountain View, CA, produced a hydrocarbon polymer membrane with improved performance and lower costs than the current per-fluorinated membranes. This cellophane like film has performed better than more common perfluorinated membranes, such as Dupont s Nafion material. The hydrocarbon membrane can also operate at higher temperatures, of up to 95°C, which allows the use of smaller radiators to dissipate heat. It also lasts 50% longer, while generating up to 15% more power and operating at lower humidity levels. 

Much of the interest in Nafion materials stems from its use as a membrane separator for chlor-alkali production and other electrochemical applications (6). Hence, it is relevant to study the material in the presence of water of swelling, with or without sorbed electrolytes. The presence of water and counterions gives us an NMR handle with which to study Nafion. Solvent and ionic mobility is rapid enough in the aqueous regions of swollen Nafion to yield high resolution NMR signals. 

Theoretical Model for the Structures of Ionomers Application to Nafion Materials... 

Martin et have evaluated the concentration and diffusion coefficients of O2 in commercial perfluorosulfonate ionomer (Nafion ) materials to assess... 

Finally, it should be mentioned that the adsorption of water on the super-acidic Nafion material is followed by protonation even at a low coverages, that is, before the appearance of 2 1 adducts (426). 

Nafion materials, and more generally perfluorinated ionomers, are particularly suitable for water and brine electrolysis and, to date, no viable alternative has been found for SPE applications. The dissolution of Nafion membranes allows the preparation of material with high porosity and high electroactive area. Such structures are required for the development of high power density SPE fuel cells. In recent work, Aldebert et al. have presented different methods for the preparation of SPE... 

Due to the unacceptably high methanol permeability of commercial Nafion, most DMFC tests are performed with relatively dilute aqueous methanol feed solutions (typically, 0.5 or 1 M). A Nafion-PBI membrane (5 wt% PBI with Nafion polymer that was 40% in the protonated form) performed well at low (1 M) and high (5 M) methanol feed concentrations, as shown in Fig. 14.19. As was the case for the Nafion-FEP and Nafion-PFA blends discussed previously, PBI-doped Nafion films contain much less fluoropolymer (2-A times less) as compared with commercial 117 membranes from DuPont, yet their performance is equal or superior to any Nafion material in a DMFC. 

Device for drying analytical gas streams using capillary membrane tubes of polar Nafion material with outer counter flow of dry carrier gas. 

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