Perfluorinated ionomer Asahi Glass

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 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. 

We will briefly introduce some important ionomers (see Fig. 1), but for a thorough treatment of ionomer chemistry, see, e.g., Refs. . The simplest classification of ionomers is semicrystalline vs. amorphous ionomers. The prototypical semicrystalline ionomer is EMAA (Surlyn, DuPont) neutralized with various cations. Also from DuPont, Nafion is a perfluorinated polyethylene with sulfonic acid or sulfonate groups on short side chains. Other commercial ionomers like Aciplex (Asahi Chemical Company), Flemion (Asahi Glass Company), and Neosepta (Tokuyama) are structurally similar to Nafion. For a recent review on Nafion see Mauritz and Moore. ... 

MAJOR APPLICATIONS Nafion is the DuPont trademark for its family of perfluorinated ionomers, that is, resins and membranes. Asahi Chemical Industry Company produces Aciplex and Asahi Glass Company, Ltd., Japan, produces Flemion both are competitive products to Nafion in form and function. These perfluorinated ionomers are used in a variety of applications, the largest of which are as an ion exchange resin and in membrane separators in the commercial electrolysis of brine to produce caustic and chlorine. Nafion membranes are also being used in the development of fuel cells and as heterogeneous super acid catalysts in supported, cubed, or powdered form. 

Fig. 17.2 Structures of some perfluorinated sulfonic acid containing polymers (PFSAs). Polymer 1 is available from DuPont (Nafion ), Asahi Glass (Flemion ), and others Polymer 2 is the short-side-chain ionomer developed at Dow, currently available from Solvacore and Polymer 3 is the ionomer available from 3M Company...

Recently, scientific literature evidenced that different companies developed per-fluorosulfonic ionomers able to sustain 120°C operating conditions for long time. In some examples the relation with linear short side chain structure is evident, most of all 3M [32] and Solvay [33,34], in other cases the polymer structure is not described, like for Asahi Glass [35] or Asahi Kasey [36], Figure 17.7 summarizes the chemical formula of the most common perfluorinated ionomers. 

Nafion ionomer is not the only perfluorosulfonic membrane material to be considered for PEMFCs. There are many other commercial perfluorinated ionomers, such as Asahi Glass (Flemion ), Asahi Kasei (Aciplex ), 3M (3M polymer), and Solvay Solexis (Hyflon ), all of which share some structural similarities with the polytetrafluoroethylene-based Nafion but use different perfluorinated vinyl ethers, as shown in Table 4.1. 

Developing ionomer membranes that are more thermostable is the most essential answer to improving their thermal durabUity. Endoh and his coworkers at Asahi Glass (Endoh, 2006) reported that their newly developed MEA, composed of a new perfluorinated polymer composite, could be operated for more than 4000 hours at 120°C and 50% RH compared to a conventional MEA, their new MEA could reduce the degradation rate to 1/100-1/1000. However, the detailed chemical structure of their new membrane has so far not been disclosed. 

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.)... 

Perfluorinated ionomer membranes have also been developed by Asahi Chemical and the Asahi Glass Company and commercialised as Aciplex S and Flemion, respectively. The general properties of the long side chain perfluorinated ionomer membranes (e.g. Nafion, Flemion, Aciplex) and the short side chain perfluorinated ionomer membranes (e.g. Dow) are shown in Table 1.2. 

---