Ionomer perfluorinated sulfone

There are a number of NMR reports on ion-exchange membranes of the Nafion type. In these ionomers, perfluorinated sulfonates are attached as pendant groups to PTFE backbones. Several of the publications [130-136]... 

Before discussing membrane chemical degradation in detail, the factors governing the degradation mechanism must be identified. Among three major types of membrane materials, hydrocarbon, partially fluorinated, and perfluorinated ionomers, perfluorinated sulfonic acid (PFSA) is the most widely used membrane material owing to its high chemical stability (Schiraldi 2006). 

Xie, T., Hayden, C., Olson, K. and Healy, J. 2005. Chemical degradation mechanism of perfluorinated sulfonic acid ionomer. In Advances in materials for proton exchange membrane fuel cell systems, Pacific Grove, CA, Feb. 20-23, abstract 24. 

The existence of ion clustering in perfluorinated sulfonate ionomers was first reported by Yeo and Eisenberg in 1975. This phenomenon has been subsequently studied for perfluorinated sulfonate and carboxylate ionomers by many Experimental evidence to support the conclusion that ion clustering occurs in these materials includes thermorheological behavior/ X-ray diffraction results/" " " IR data/ " NMR data,"" " ESR data/ Mossbauer spectroscopic fluores-... 

In a previous paper (2), the author described a method to dissolve the sulfonyl fluoride precursor form of a perfluorinated sulfonate ionomer. Commercially available forms of Nafion are supplied as activated membranes (i.e., saponified from the precursor to the ionic form), and near-quantitative reconstitution of the precursor functionality (such as RSOjF) must first be performed using a chemical reagent such as SF. f4) before dissolution in perhalogenated solvents is possible. Besides adding to the cost of membrane manufacture, SF. is extremely toxic and corrosive and must be handled in nickel alloy pressure equipment. Therefore, a method for dissolving perfluorinated ionomers directly would be more desirable. 

There are two types of polymeric electrolyte, based on their conduction mechanisms. The first group is the polyelectrolyte in which the polymer itself contains an anionic or cationic group, usually on a side chain. The counter-ions for these groups are typically small, inorganic ions that are mobile within the polymer matrix. Nafion, a perfluorinated sulfonated ionomer made by du Pont, is an example of this type of electrolyte [1]. Nafion has been used as the electrolyte in several amperometric gas sensors. 

Although there have been various membranes used, none is more researched or seen as the standard than the Nafion family by E. I. du Pont de Nemours and Company. Like the other membranes used, the general structure of Nafion is a copolymer between polytetrafluoroethylene and polysulfonyl fluoride vinyl ether. These perfluorinated sulfonic acid (PFSA) ionomers exhibit many interesting properties such as a high conductivity, prodigious water uptake, and high anion exclusion to name a few. Nafion is the main membrane studied in this chapter. 

The majority of solid proton-conducting membranes, most commonly used in contemporary fuel cell technology, are hydrated perfluorinated sulfonic acid ionomers. In recent years, enormous programs in membrane research have explored empirically how various modifications of the benchmark material, viz. Nafion, affect the physical membrane properties. The main modifications include (1) varying the hydrophobic/hydrophilic composition of the polymer, (2) controlling the grafting density and lengths of the sidechains,... 

Firstly, Nafion and other perfluorinated sulfonic acid ionomers will be discussed, along with inorganic- and organic-Nafion based composites. Secondly, we will introduce non-fluorinated single and composite membranes, including membranes for high temperature DAFC. Finally we will discuss anion conducting membranes for alkaline DAFC. 

Liu H, Gasteiger HA, LaConti AB, Zhang J (2006) Factors impacting chemical degradation of perfluorinated sulfonic acid ionomers. ECS Trans 1 283-293... 

Perfluorinated sulfonic acid containing polymers (PESAs) are the most commonly used membrane materials in fuel cells today. Membranes made from these ionomers provide the benefits of highly acidic pendant acid groups for high proton conductivity, good mechanical properties, excellent chemical stability, and fairly... 

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... 

Xie, T. and Hayden, C. A. 2007. A kinetic model for the chemical degradation of perfluorinated sulfonic acid ionomers Weak end groups versus side chain cleavage. Polymer 48 5497-5506. 

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.)... 

This chapter is a survey of the fundamental studies on perfluorinated sulfonic iono-mer membranes including ionomer synthesis, membrane characterization, membrane... 

Du Font s Nafion membranes have been the first truly successful membranes in these applications. They are made of a perfluorinated and sulfonated polyal-kylene ionomer (-CFj- or >CF- throughout). Such a composition leads to... 

Ionomer membranes are used in fuel cells in order to separate the anode and cathode compartment and to allow the transport of protons from the anode to the cathode. The typical membrane is Nation , which consists of a perfluorinated backbone and side chains terminated by sulfonic groups. In the oxidizing environment of fuel cells, Nation , as well as other membranes, is attacked by reactive oxygen radicals, which reduce the membrane stability. Direct ESR was used recently in our laboratory to detect and identify oxygen radicals as well as radical intermediates formed in perfluorinated membranes upon exposure to oxygen radicals [73,74]. The three methods used to produce oxygen radicals in the laboratory and the corresponding main reactions are shown below. 

For instance, the Dow experimental membrane and the recently introduced Hyflon Ion E83 membrane by Solvay-Solexis are "short side chain" (SSC) fluoropolymers, which exhibit increased water uptake, significantly enhanced proton conductivity, and better stability at T > 100°C due to higher glass transition temperatures in comparison to Nafion. The membrane morphology and the basic mechanisms of proton transport are, however, similar for all PFSA ionomers mentioned. The base polymer of Nation, depicted schematically in Figure 6.3, consists of a copolymer of tetrafluoro-ethylene, forming the backbone, and randomly attached pendant side chains of perfluorinated vinyl ethers, terminated by sulfonic acid head groups. °... 

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