Polymer Membranes for High Temperatures

Polyphosphazene sulfonic acids [200, 201] offer a unique combination of inorganic backbone with high stability, high ionic density and structural diversity with crosslinking alternatives. Polyphosphazenes with sulfonamide functionalization have been reported with high proton conductivity [202]. 

A big challenge for fuel-cell membranes is a good performance at temperatures higher than 100°C. Reviews on materials under investigation to overcome this problem have been published by Alberti and Casciola [203], Li et al. [204] and Hogarth et al. [205]. 

Polybenzimidazole (PBI) (initially manufactured by Hoechst-Celanese, now PE ME A) is one of the few polymers under consideration for high-temperature operation. The application of PBI [206, 207] and the noncommercial AB-PBI [208] in fuel cells was introduced by Savinell and coworkers. For that, the membrane was immersed in concentrated phosphoric acid to reach the needed proton conductivity. Operation up to 200 °C is reported [209]. A disadvantage of this class of membranes is the acid leaching out during operation, particularly problematic for cells directly fed with liquid fuels. Additionally, the phosphoric acid may adsorb on the platinum surface. A review on membranes for fuel cells operating above 100 °C has been recently published [209]. 

Phosphonated polymers have been proposed for fuel cells with the expectation of being thermally more stable and better retaining water than sulfonic groups [210, 211]. Phosphonated poly(phenylene oxide) [212], poly(4-phenoxy-benzoyl-l,4-phenylene) [213] and polysulfones [214, 215] have been reported. Phosphonated fluoromonomers were polymerized [164]. Characterization of phosphonated films in terms of their proton conductivity has been reported for some of the phosphonated polymers polyphosphazene [216], trifluoropolysty-rene [217], poly(4-phenoxybenzoyl-l,4-phenylene) [218]. Relatively low conductivity values were reported for most of the polymers prepared up to now. The values for polyphosphazene [216] and for perfluorocarbon polymers [219] were quite encouraging. Phosphonated poly(phenylene oxide) [211] was evaluated in fuel cell-tests. 

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Li, Q. et al., PBI-based polymer membranes for high temperature fuel cells preparation, characterization and fuel cell demonstration. Fuel Cells, 4, 147, 2004. 

Bose S, Kuila T, Thi XLN, Kim NH, Lau KT, Lee JH (2011) Polymer membranes for high temperature proton exchange membrane fuel cell recent advances and challenges. Prog Polym... 

Bhadra S, Kim NH, Lee JH (2010) A new selfcross-linked, net-structured, prohm conducting polymer membrane for high temperature proton exchange membrane fuel cells. J Membr Sci 349 304-311... 

Li Q, He R, Jensen JO et al (2004) PBI-based polymer membranes for high temperature fuel cells— preparation, characterizations and fuel cell demonstrations. Fuel Cells 4 147-159... 

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