Membranes perfluoro-sulfonic acid materials

Many different types of polymer membranes containing fixed ionic groups have been explored since. Up to today, the materials of choice are perfluoro sulfonic acid membranes of the Nafion-type (Fig. 2), for the first time described by (jrot [9]. These materials, similar products have later been developed by other companies (Asahi Glass, Asahi Kasei, Solvay, 3M, Gore, etc.), have been continuously improved for their application in fuel cells. A comprehensive overview of membrane development can be found in [10]. 

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.)... 

The most widely studied fuel-ceU membrane is DuPont s Nafion , a copolymer of tetrafluoroethylene and perfluoro(4-methyl-3,6-dioxa-7-octene-l-sulfonic acid). Nafion is the membrane material of choice for most proton-exchange membrane fuel cells that operate at a temperature <80 °C. While Nafion offers high conductivity combined with exceptional chemical and mechanical stability [3], it suffers from several critical drawbacks. When used in a direct methanol fuel cell, Nafion shows significant methanol leakage (crossover from the anode to the cathode) with the resultant reduction in fuel-ceU performance. To overcome this shortcoming the methanol concentration in the anode feed is usuaUy reduced to 0.5-2.0 M, which necessitates... 

Nafion is an ionomer that has a hydrophobic tetrafluoroethylene (TFE) backbone and perfluoro alkyl ether (PFAE) side chains terminated with hydrophilic sulfonate salt [1 ], as shown in Fig. 1. It was introduced by DuPont in 1960 and has been used in a variety of applications such as an ion-selective membrane for the Qilor-Alkali process [5, 6], a water transport membrane for humidifiers, and as a strong acid catalyst [7]. Nafion was introduced as a polymer electrol34e membrane (PEM) in fuel cells in the early 1990s [4, 8]. Compared to hydrocarbon membranes, Nafion was chemically more robust in the fuel cell and the acid form has high proton conductivity. There have been many efforts to find alternative membrane materials... 

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