Nafion, Flemion membrane conductivity

Later, Hinatsu et al. studied the uptake of water, from the liquid and vapor states at various temperatures, in acid form Nafion 117 and 125, and Aciplex and Flemion membranes, although the latter two similar products will not be discussed here. These studies were motivated by a concern over the deleterious effects, involving either overly dry or overly wet membranes, on electrical conductivity within the context of polymer electrolyte fuel cells and polymer electrolyte water electrolyzers. 

Despite perfluorinated polymer electrolytes (Nafion, Flemion, Aciplex) having been used extensively in PEMFCs, their poor thermal mechanical stability (low Tg), high methanol permeability, and extremely high production costs have led to limitations of their large-scale application. Therefore, a variety of hydrocarbon polymer electrolytes have been developed during the past decade, with the greatest emphasis placed on the costs, conductivity, and durability of these materials. At the same time, the poor mechanical stability and inadequate durability of the hydrocarbon polymer membranes were identified as the main barriers to their practical application. 

As discussed in the previous sections, the hydrated cation migration under an applied electric field directly results in the deformation of the material. In fact, when ionomer (Nafion, Flemion) is dry, the interaction between the side chain groups and the cations is very strong and the ionic conductivity of the membrane is very small [Takeji et al. (1982)]. Conversely, when the membrane is hydrated, the interaction between the cations and the anions in the side chains is weakened and it results in bet-... 

The development of new polymeric materials for polymer electrolyte fuel cell is one of the most active research areas, aiming at the new energy sources for electric cars and other devices. The mainstream of the material research for fuel cell is perfluoroalkyl sulfonic acid membranes such as Nafion, Acipex, and Flemion. The most well-known one is Nafion of Du Pont, which is derived from copolymers of tetrafluoro-ethylene and perfluorovinyl ether terminated by a sulfonic acid group.Protons, when dissociated from the sulfonic acid groups in aqueous environment, become mobile and the membrane becomes a proton conducting electrolyte membrane. 

Typically, the membranes for low-temperature PEM fuel cells are made of perfluoiocaibon-sulfonic acid ionomers (PFSA). The best material known is Nafion produced by DuPont, though similar materials have been developed for commercial or development purposes by other manufacturers such as Asahi Glass (Flemion) or As Chemical (Aciplex). In the electrode part, the catalyst is generally dispersed as small particles on a conductive support (carbon powders). Despite many attempts to develop a non-noble-metal catalyst, platinum remains the best known electrocatalyst for ORR in PEM fuel cells. The most extensive limitations to large-scale commercial use of these materials arise from the fact that... 

Figure 5.3 Water content of (a) Nafion 117, (b) Flemion F-1.44 and (c) Flemion F-1.8 membranes of various ionic forms. Abbreviations used for alkyl ammonium ions are TMA, TEA, TPrA, TBA for tetramethyl, tetraethyl, tetrapropyl and tetrabutyl ammonium ions, respectively (Reprinted with permission from Asaka, K., Fujiwara, N., Oguro, K. et al. State of water and ionic conductivity of solid polymer electrolyte membranes in relation to polymer actuators, J. Electroanalytical Chem., 505 (1 2), 24-32. Copyright (2001) Elsevier).

The success of DuPont s Nafion spurred the development of other polymeric materials with similar chemical architecture. The most notable material developments have been the Dow experimental membrane (Dow Chemicals), Flemion (Asahi Glass), Aciplex (Asahi Kasei), as well as Hyflon Ion and its most recent modification Aquivion (SolviCore). In addition to excellent ionic conductivity, materials of the PFSA family, illustrated in Figure 2.2, exhibit exceptional stability and durability in highly corrosive acidic environments, owing to their Teflon-like backbone (Yang et al., 2008 Yoshitake and Watakabe, 2008). 

FIGURE 4.4 Arrhenius plots for ionic conductivities (a) of Flemion X-form (X = H, Li, Na) membranes, along with Nafion 117 H-form in the fully hydrated state [66]. 

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