Perfluorinated ionomer duPont

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—... 

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... 

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. 

Perfluorosulfonic add (PFSA) membranes continue to be the industry standard for low-temperature PEMFCs due to their excellent proton conductivity, mechanical and chemical stability that is difficult to surpass. The Nafion membrane produced by DuPont has been the most studied (Mauritz and Moore, 2004 Grot, 2008). Nafion membranes are coded according to the polymer equivalent weight (EW) (first two digits), the membrane thickness (in mil, 1/1000 inch, corresponding to 25 pm) - third, or third and fourth digits) thus Nafion N117 is polymer EW 1100,7 mil thickness. In parallel with these developments, advances have been made on related perfluorinated ionomers that differ from the Nafion -type polymer... 

The ideal cell potential between the two half-reactions for H2/O2 is 1.23 V at 25 °C. The actual cell voltage will be lower due to losses in the cell. As the current is increased from the open circuit condition, catalytic activation losses (dominant at the cathode) will initially reduce the voltage to 1V. Ohmic losses due to ionic resistance through the membrane and electrical resistance in the assembly (to a lesser extent) will further reduce the voltage in a linear fashion with current. The most common polymer electrolyte is Nation (trademark of DuPont), which is a perfluorinated ionomer that must be humid to maintain good ionic conductivity. A limiting current will then be achieved, beyond which the mass transport of reactants (typically oxygen at the cathode) becomes insuffi-... 

The first perfluorinated ionomer was developed in the early 1960s by Walther G. Grot at E.I. DuPont de Nemours (Grot, 2011). It became famous under the trade-name Nafion. From the mid-1960s, Nafion found use as an electrochemical separator material in the chlor-alkali industry. Exploration of Nafion as a fuel cell electrolyte started at about the same time. 

In the early 1960 s, Dupont de Nemours produced the first perfluorinated ionomer membrane the Nafion. The chemical formula of this ionomer is ... 

The development of perfluorinated membranes by DuPont during the 1960s has played a vital role in electrochemical system applications. The Nafion family or perfluorinated ionomer membranes meet the requirements for several electrochemical systems (chloroalkafine, fuel cells and some other non-fuel cell applications). A lifetime of over 60000 hours has... 

The high EWs of the first Nafion membranes family limited their use in fuel cells and prompted the development of the Dow membrane. This membrane is structurally and morphologically similar to the Nafion membrane, but differs with respect to its EWs, which are typically in the 800 to 850 range, and have shorter size chains (z = 0 for Dow and z = 1 for Nafion) (Utracki and Weiss, 1989). The Dow membranes are a short side chain perfluorinated ionomer whereas the Nafion membranes are the long side chain perfluorinated ionomer. The specific conductance of 800 and 850 EW experimental membranes has been reported as 0.20 and 0.12 Q cm", respectively (Savadogo et al, 1995). It must be pointed out that the Dow monomer is more complicated to elaborate than the DuPont monomer. Therefore, the synthesis of the Dow epoxy is more complicated than that of the Nafion, which is a commercially available material (Savadogo et al, 1995). 

Nafion ionomers were developed and are produced by the E. I. DuPont Company. These materials are generated by copolymerization of a perfluorinated vinyl ether comonomer with tetrafluoroethylene (TEE), resulting in the chemical structure given below. 

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. ... 

It is mainly the PEM that distinguishes a PEM fuei ceii from aii other types of fuel cells. As its name implies, a PEM has the capability of transporting protons. It is typicaiiy made of a solid ionomer with acidic groups such as sulfonic acid (-SO3H) at the end of the polymer side chains. Polystyrene sulfonic acid is one such ionomer, and it was used as the PEM in the early days of the PEM fuel cell development around the 1960s. However, since the PEM fuel cell environment is warm, corrosive, and oxidative (at cathode), an ionomer with higher chemical and electrochemical stability is required. State-of-the-art PEMs are made of perfluorinated polysulfonic acids, and include DuPont s Nafion . 

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...

Nafion a perfluorinated sulfonic acid ionomer manufactured by DuPont... 

Excellent reviews on chemical structure, morphology and properties of acid-bearing polymers can be found in Mauritz and Moore (2004), Peckham and Holdcroft (2010) and Yang et al. (2008). The base polymer of the prototypical DuPont Nafion perfluorosulfonic acid (PFSA) ionomer, shown in Figure 1.13(left), consists of a tetrafluoroethylene (TFE) backbone with randomly attached pendant sidechains of perfluorinated vinyl ethers. Sulfonic acid groups are fixed at the sidechain heads (Kreuer et al., 2004 Tanimura and Matsuoka, 2004 Yang et al., 2008 Yoshitake and Watakabe, 2008). 

As often represented by Nafion, which was commercialized by Dupont in the late 1960s, perfluorinated membrane has been the most commonly used ionomer material... 

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