Fluorinated Ionomer Membranes

The experimental collection efficiencies for H202 (estimated Graham s law diffusion coefficient is 0.18 cm2/s) for an aqueous scrubber Nafion (per-fluorinated ionomer) membrane DS (L = 40 cm, d0 = 0.5 cm, and d = 0.06 cm) have been experimentally determined by two independent ap-... 

Heitner-Wirguin, C. Recent advances in per-fluorinated ionomer membranes structure, properties and applications. J. Membr. Sci. 1996, 120 (1), 1-33. 

M. Saito, S. Tsuzuki, K. Hayamizu, T. Okada, Alcohol and proton transport in per-fluorinated ionomer membranes for fuel cells, J. Phys. Chem. B 110 (2006) 24410-24417. 

Partially fluorinated ionomer membranes Among this material class is the BAM3G membrane type composed of sulfonated or phosphonated poly(a,(5,(5-trifluorostyrene) and its copolymers [2-4] and the different types of grafted membranes based on partially fluorinated polymer foils, as developed by Scherer [5], Sundholm [6], and others. 

Table 8.5 Properties of nonfluorinated and partially fluorinated ionomer membranes...

New electrolyte formulation Non-fluorinated ionomer membranes such as phosphazene, arylene, poly(benzimidazole) or FBI, hydrocarbon polymers, nanoporous silicon membranes to serve as proton conductors (Apanel et al., 2(X)4 Chu et al., 2(X)5). 

Oxiranes (epoxides) are important intermediates in syntheses and for industrial processes, which produce useful compounds of high practical importance,17,18 e.g. inert fluids, elastomers, and ionomer membranes. The epoxidation reaction of highly fluorinated C = C bonds are occasionally, especially in acidic media, accompanied by rearrangement of the primary epoxides (see Section 5.3.3.2.) and, in the case of stronger oxidants, by C = C bond cleavage (vide infra, see also Vol. ElOb/Part 1, p691 ff). 

Major areas of application are in the field of aqueous electrochemistry. The most important application for perfluorinated ionomers is as a membrane separator in chloralkali cells.86 They are also used in reclamation of heavy metals from plant effluents and in regeneration of the streams in the plating and metals industry.85 The resins containing sulfonic acid groups have been used as powerful acid catalysts.87 Perfluorinated ionomers are widely used in worldwide development efforts in the held of fuel cells mainly for automotive applications as PEFC (polymer electrolyte fuel cells).88-93 The subject of fluorinated ionomers is discussed in much more detail in Reference 85. 

Inorganic/Organic (Fluorinated) Composite Ionomer Membranes... 

The use of low-cost basic polymers instead of Nation is an interesting alternative [19,20].The development of new polymers for ionomer membranes including perfluorinated ionomers, partially fluorinated ionomers, nonfluorinated ionomers, high-molecular/low-molecular composite membranes as well as novel polymer modification processes and novel membrane materials is summarised in [21]. 

Gore-Select membrane is a recent innovation that is useful for fuel cells. The membrane is made by filling the pores of Gore-Tex (expanded PTFE) with a per-fluorinated ionomer Hke Nafion. The resulting membrane is about 20 pm thick, about one tenth the thickness of a Nafion membrane, and it has about half the resistance of Nafion. Membrane-electrode assembhes are made by applying platinum black coatings (0.3 mg/cm ) to both surfaces. They are reported to perform well in fuel cells [46]. 

Copolymers of tetrafluoroethylene and sulfonic acid functional per-fluorinated monomers (e.g., Nafion, Dow s perfluorosulfonic acid (PFSA)) have high water permeability. Water transport through these ionomer membranes has been investigated. The non-Fickian diffusion process is analyzed by a thermodynamic approach. The results provide some useful insights into the behavior of these materials as dehydration membranes. 

There is no doubt that the perfluorinated ionomer membranes take initiative in this field and contribute a great deal in the commercialization and wide diffusion of fuel cells in the early stage. In terms of environmental compatibility (recyclability or disposability) and production cost, the perfluorinated ionomer membranes should be replaced with non-fluorinated alternative materials within the next decade. Challenge is how to achieve comparable conductivity and durability with the non-fluorinated membranes. Currently, no alternative materials have overcome the trade-off relationship between these two conflicting properties. In addition to the... 

Polymers with hydrocarbon backbone (and generally no fluorine groups) and acidic functions. Phase-separated morphology of ionomer membranes based on the differences in the hydrophilicity (and hydrophobicity) of the components. 

Low cost (final target for electric vehicle apphcations would be cheaper than US 10/m ) need to be taken into account. While a number of PEMs have been developed, no single membranes fulfill aU of these requirements. Currently, the most promising PEMs are perfluoro sulfonic acid (PFSA) ionomers. Another candidate second to the PFSA ionomers is non-fluorinated (or in some cases only slightly fluorinated) hydrocarbon ionomers. The aim of this chapter is to review the most recent progress on these two classes of ionomer membranes for low-temperature fuel cell applications... 

Fluorinated ionomers are known for their use as ion-permeable electrolyte membranes most commonly in chloro-alkali electrolysis, electrochemical devices, and H2/O2 fuel cells. The polymer membrane facilitates the transport of protons between... 

From the reviewed work, it can be concluded that obviously the use of partially fluorinated aromatic cationomers as ionical cross-linkers leads in most cases to better chemical and thermal stabilities of the blend membranes than if nonfluorinated cationomers would be applied as acidic blend components. Among aU acidic cross-linkers, the sulfonated and partially fluorinated ionomer S9 (Fig. 4.5) leads to the best chemical stability of the referring base-excess PBI blend membranes. 

Kerres J, Xing D, Schonberger F (2006) Comparative investigation of novel FBI blend ionomer membranes from nonfluorinated and partially fluorinated polyaryiene ethers. J Poiym Sci B Polym Phys 44 2311-2326... 

Yandrasits M (2011). New fluorinated ionomers for proton exchange membranes . In Advances in New Materials for Proton Electrolyte Fuel Cell Sjvife/Mi, Asilomar, CA. 

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