Partially fluorinated membranes

Gege, C., Schneider, M. F., Schumacher, G., et al. (2004) Functional microdomains of glyco-lipids with partially fluorinated membrane anchors Impact on cell adhesion. ChemPhysChem, 5(2), 216-224. 

In recent years, many kinds of materials have been developed to synthesize proton-conducting membranes for H2/air PEM fuel cells, and some have exhibited promising performance as potential candidates to replace PFSA membranes. The major membranes are (1) fluorinated membrane, (2) partially fluorinated membrane, (3) nonfluorinated (including hydrocarbon) membrane, and (4) nonfluorinated composite membrane. Among these, the hydrocarbon membrane is considered a promising alternative due to its low cost compared with PFSA membranes [61]. 

Those critical functions of membrane for DMFC are simple but most important. Required functions are ionic conductivity, electrical insulation, gas and liquid (especially methanol) tightness, and chemical and mechanical stability. As indicated in Fig. 13.2, ohmic polarization is mainly due to the ionic resistance of membranes, but the low open circuit potential of cathode is also mainly coming from the voltage drop by mixed potential made of fuel crossover through the membrane. The low cost of material and process is also another factor in terms of commercialization. Especially for mobile applications, membranes have the additional function for mass balance of liquid fuel and water products circulated out of or through the membrane. In this manner, alternative membranes are under development and researchers are focused on four types perfluorinated and partially fluorinated membranes hydrocarbon and composite and other ionomer modifications inorganic materials. The current state of the art and technical approaches to these materials are discussed in detail elsewhere in this volume. 

Kim has improved the mechanical properties of partially fluorinated membranes and confirmed their performance by PEMFC and DMFC operation [49],... 

Direct fluorination of polymer or polymer membrane surfaces creates a thin layer of partially fluorinated material on the polymer surface. This procedure dramatically changes the permeation rate of gas molecules through polymers. Several publications in collaboration with Professor D. R. Paul62-66 have investigated the gas permeabilities of surface fluorination of low-density polyethylene, polysulfone, poly(4-methyl-1 -pentene), and poly(phenylene oxide) membranes. 

An alternative approach to the use of partially fluorinated systems to reduce the cost of fluorinated PEMs has been developed by DeSimone et al. a perfluo-rinated vinyl ether is copolymerized with a hydrocarbon monomer (styrene), sulfonated, and then subsequently fluorinated to replace existing C-H bonds with C-E bonds (Eigure 3.18). Thus yields the perfluorinated, cross-linked sul-fonyl fluoride membrane that can then be hydrolyzed to give the PEM (7). Because the membranes are cross-linked, considerably higher acid contents (up to 1.82 meq/g) are possible for these materials in comparison to Nafion, leading also to higher proton conductivity values. 

Buchi, F. N., Gupta, B., Haas, O. and Scherer, G. G. 1995. Performance of differently cross-linked, partially fluorinated proton-exchange membranes in polymer electrolyte fuel cells. Journal of the Electrochemical Society 142 3044—3048. 

Mokrini, A., Huneault, M. A. and Gerard, P. 2006. Partially fluorinated proton exchange membranes based on PVDF-SEBS blends compatibilized with methylmethacrylate block copolymers. Journal of Membrane Science 283 74—83. 

Within the realm of BAM2G membranes, a series of partially fluorinated bisphenol A-type poly(arylether) sulfones were synthesized. As mentioned above, these materials initially exhibited acceptable, useful service-life performance, but were unable to provide more than 500 h of continuous running time. This led to the decision that a perfluorinated backbone would be most beneficial in achieving fuel cell longevity in performance and efficiency. Therefore, the a, 3,p-trifluorostyrene monomer was chosen as the most suitable platform on which to build BAM3G polymers [98]. The BAM3G has demonstrated over 100,000 h of cumulative performance in a wide variety of Ballard fuel cell hardware. The BAM3G membranes have... 

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]. 

The chemical nature of the base polymer is an important aspect in membrane development. There has been preference for the thermally stable fluorinated polymers over hydrocarbon polymers. Fluorine-containing polymers, characterized by the presence of carbon-fluorine bonds, are widely used as the base matrices owing to their outstanding chemical and thermal stability, low surface energy, and the ease of modiflcation of various properties by the grafting method. Per fluorinated polymers and partially fluorinated polymers combining hydrocarbon and fluorocarbon structures are excellent candidates as base polymers. For instance, fluorinated FEP has drawn wide attention due to its reasonably good radiation stabiUty [58]. 

Radiation grafting has been investigated now for several years as an attempt to balance cost and stability in the development of proton-conductive membranes. Partially fluorinated polymers like perfluoroethylenepropylene (FEP) [159-161] or poly(vinylidene fluoride)(PVDF) [162, 163] are submitted to gamma [159, 160] or electron [162, 163] radiation and immersed in a mixture of styrene and divinyl benzene (for crosslinking) ... 

Y. Chang, Y.B. Ixe, C. Bae, Partially fluorinated sulfonated poly(ether amide) fuel cell membranes influence of chemical structure on membrane properties. Polymer 3 (1) (2011) 222-235. 

A partially fluorinated polymer, also soluble in polar solvent, is PVDF. It is characterized by high performance, chemical resistance, good thermal stability, and resistance to UV light and oxidant attack (Chin et al., 2006). PVDF membranes have been used primarily in the construction of submerged modules, widely used in bioreactors because of their lower costs with respect to other types of photocatalytic membranes (Sopajaree et al., 1999 Chin, Lim, Chiang, Fane, 2007 Jia et al., 2006, Fu, Ji, Wang, Jin, An, 2006). 

Li Y, Roy A, Badami AS, Hill M, Yang J, Dunn S, McGrath JE (2007) Synthesis and characterization of partially fluorinated hydrophobic-hydrophilic multiblock copolymers containing sulfonate groups for proton exchange membrane. J Power Sources 172 30... 

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