Perfluorosulfonate polymer transport properties

The water distribution within a polymer electrolyte fuel cell (PEFC) has been modeled at various levels of sophistication by several groups. Verbrugge and coworkers [83-85] have carried out extensive modeling of transport properties in immersed perfluorosulfonate ionomers based on dilute-solution theory. Fales et al. [109] reported an isothermal water map based on hydraulic permeability and electro-osmotic drag data. Though the model was relatively simple, some broad conclusions concerning membrane humidification conditions were reached. Fuller and Newman [104] applied concentrated-solution theory and employed limited earlier literature data on transport properties to produce a general description of water transport in fuel cell membranes. The last contribution emphasizes water distribution within the membrane. Boundary values were set rather arbitrarily. 

H.L. Yeager, Transport Properties of Perfluorosulfonate Polymer Membranes. In A. Eisenberg and H.L. Yeager (eds), Perfluorinated lonomer Membranes, ACS Symposium Series, 180, American Chemical Society, Washington, D.C (1982), p. 41. 

Phillips AK, Moore RB (2006) Mechanical and transport property modifications of perfluorosulfonate ionomer membranes prepared with mixed organic and inorganic counterions. J Polym Sci B Polym Phys 44(16) 2267-2277... 

Due to their extensive use in the polymer industry and as solvents, there is a continuing need for better separation processes for alkenes and other unsaturated organic compoimds from alkanes. Perfluorosulfonic acid (PFSA) membranes, such as Nafion (1), that have been ion-exchanged with silver(I) ion exhibit large transport selectivities for many unsaturated hydrocarbons with respect to saturates with similar physical properties. These selectivities are the result of reversible complexation reactions between the unsaturated molecules and Ag+ (2-4), which results in facilitated transport through the membranes (5). 

Polymer electrolyte fuel cells (PEFCs) are unique in that they are the only variety of low-temperature fuel cell to utilize a solid electrolyte. The most common polymer electrolyte used in PEFCs is Nafion , produced by DuPont, a perfluorosulfonic ionomer that is commercially available in films of thicknesses varying from 25 to 175 pm. This material has a fluorocarbon polytetrafluoroethylene (PTFE)-kbone with side chains ending in pendant sulfonic acid moieties. The presence of sulfonic acid promotes water uptake, enabling the membrane to be a good protonic conductor, and thereby facilitating proton transport through the cell. This chapter reviews PEFC development, structure, and properties and presents an overview of PEM technology to date. 

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