Perfluorinated sulfone ionomers

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. 

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. 

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]... 

Since the conductivity of electrolytes and the cross section and thickness of the membrane are known, a can be determined from the voltage drops across the three pairs of probe electrodes 1-2, 3-4 and 5-6. The sodium current efficiency (CE) can also be determined by titrating the amount of caustic soda generated over a given period of time. The confinement chambers around the working electrodes are used to eliminate free bubbles near the membrane. Our normalized transport data for sulfonate, carboxylate and sulfonamide ionomers are plotted In Figure 5 the universal percolative nature of perfluorinated ionomers can be clearly eeij. The prefactor sulfonate ionomers. The exponent t is 1.5 0.1 in reasonable agreement with theory and the thresholds are between 8 to 10 vol. %, which are consistent with the bimodal distribution in cluster size postulated by the cluster-network model (5.18). This theory has also been applied recently to delineate sodium selectivity of perfluorinated ionomers (20). 

The perfluorinated, carboxylated and sulfonated ionomer membranes form the ionic clusters of a few nm in size, as in the case of the hydrocarbon-based ionomers such as polyethylene,polystyrene and polybutadiene(9). The ionic clusters strongly affect physical properties of the membranes, e.g., the swelling behavior of the membranes (amount of water uptaken by the membranes, W and... 

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... 

Hensley, J. E. and Way, J. D. 2007. Synthesis and characterization of perfluorinated carboxylate/sulfonate ionomer membranes for separation and solid electrolyte applications. Chemistry of Materials 19 ... 

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. 

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). 

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

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