Nafion polymer blend

Nafion in the bulk phase separates into hydrophobic and hydrophilic SO3H regions. The ionic domains or clusters are inverted micelles surrounded by a fluorocarbon matrix, and the ionic domains are connected by short channels. Because of the inverted micelle within the fluorocarbon matrix, availability of the acid sites for catalysis is greatly diminished. Two approaches were initially used to increase the catalytic activity of bulk Nafion polymer blends (2) and coating a liquid conposition of Nafion on a hydrophobic support (3). 

Stable highly conductive films of PPy-Nafion-impregnated Gore-tex and PPy-Nafion have also been reported. Polymer blends can also be produced by... 

Treatment of PVDF by dehydrofluorination and doping with sulfuric acid prior to blending have been shown to improve the hydrophilicity of a Nafion/PVDF blend. Such blends were demonstrated to show comparable conductivity and FC performance to unmodified Nation and significantly improved over blends in which the PVDF had not been treated. MeOH crossover rates, however, were not reported. PEMs composed of "sandwiches" of Nation plus Nafion/PVDF blends have also been used as PEMs in order to reduce MeOH crossover and improve DMFC performance. - Other non-ionic polymers that have been blended with Nation include PPCF and polypyrrole. 21... 

FTIR spectroscopy has been applied in the study of polymer blends including Neoprene rubber, chlorosulfonated PE, nitrile rubber, polyvinyl chloride (PVC) containing carbon black and other fillers [86], Nylon 6 inorganic [87], polyhydroxyether sulfone/poly(N-vinyl pyrrolidone) [88], graphite-based low-density polyethylene [89], caprolactone/Nafion blends [90], polybutylene terephthalate/polyamide [91], polyphenylene sulfide/acrylonitrile - butadiene - styrene [92], PMMA/polypyrrol [93], and lower or high performance liquid chromatography (LDPE/HDPE) [94]. 

Blending Nafion polymer with other polymeric materials has also been tried by some researchers, hi one such study, poly(l-methylpyrrole) has been impregnated with commercial Nafion membrane by in situ polymerization. A decrease of more than 90% in the permeability of the membranes to methanol is reported, although the ionic resistance of such heavily loaded membranes became too high for high-power fuel cells. At lower poly(l-methylpyrrole) loadings, a decrease in methanol permeability by as much as 50% could be realized without a significant increase in ionic... 

Membrane prepared by blending sulfonated polybenzimidazole (PBI) with Nafion polymer showed a conductivity of 0.032 S cm The methanol permeability of the composite membrane was found to be 0.82 x 10 cm s as compared to Nafion, which is around 2.21 x 10 cm s [22]. Addressing the problem of methanol permeation, a composite membrane of Nafion with polyvinyl alcohol (PVA) for direct methanol fuel cell has been reported. It is concluded that at the weight ratio of 1 1 in PVA and Nafion, the thin film-coated Nafion membrane exhibited low methanol crossover, and the membrane protonic conductivity could be improved by the sulfonation treatment [23]. Recently, Zaidi et al. [24] prepared composite membranes of PFSA ionomer with boron phosphate and showed the conductivity of 6.2 X 10-2 S cm-i at 120°C. 

With the exception of the inorganic acid doped PBI system, no membrane (such as PEO [119], PVA [122], polyacrylamide (PAAM) [116,117,123], polyethylenimine (PEI) [120], and poly diallyl-dimethyl-anunonium-dihydrogen phosphate, PAMA -H PO " [115] has demonstrated conductivities superior to Nafion at temperatures >100°C and low relative humidities (ambient pressure operating conditions). Most of these acid-polymers blend exhibit proton conductivity <10" S cm" at room temperature. High acid contents result in high conductivity but poor mechanical... 

Due to the unacceptably high methanol permeability of commercial Nafion, most DMFC tests are performed with relatively dilute aqueous methanol feed solutions (typically, 0.5 or 1 M). A Nafion-PBI membrane (5 wt% PBI with Nafion polymer that was 40% in the protonated form) performed well at low (1 M) and high (5 M) methanol feed concentrations, as shown in Fig. 14.19. As was the case for the Nafion-FEP and Nafion-PFA blends discussed previously, PBI-doped Nafion films contain much less fluoropolymer (2-A times less) as compared with commercial 117 membranes from DuPont, yet their performance is equal or superior to any Nafion material in a DMFC. 

Trogadas and Ramani summarized the modification of PEM membranes, including Nafion modified by zirconium phosphates, heteropolyacids, hydrogen sulfates, metal oxides, and silica. Membranes with sulfonated non-fluorinated backbones were also described. The base polymers polysulfone, poly(ether sulfone), poly(ether ether ketone), polybenzimidazole, and polyimide. Another interesting category is acid-base polymer blend membranes. This review also paid special attention to electrode designs based on catalyst particles bound by a hydrophobic poly-tetrafluoroethylene (PTFE) structure or hydrophilic Nafion, vacuum deposition, and electrodeposition method. Issues related to the MEA were presented. In then-study on composite membranes, the effects of particle sizes, cation sizes, number of protons, etc., of HPA were correlated with the fuel cell performance. To promote stability of the PTA within the membrane matrix, the investigators have employed PTA supported on metal oxides such as silicon dioxide as additives to Nafion. 

Alternatively, CNT-polymer composites have been utilized as polymer electrolyte membranes in fuel cell devices (PEMFCs) [111]. Sulfonic acid-functionalized CNTs were blended with Nafion polymer so that the proton transport capability of the polymer matrix could be enhanced appreciably. Ionic conductivity measurements of Nafion and CNT-Nafion membranes revealed almost one order of magnitude higher conductivity for the composite than that for neat matrix. 

Pasupathi et al. fabricated an acid-base polymer blend membrane based on sulfonated poly(etheretherketone) and poly(benzimidazole) for direct methanol fuel cells. A SPEEK/PBI membrane demonstrated a noticeable enhancement in the DMFC performance compared with Nafion 117. The maximum power densities (45 mW cm ) obtained with SPEEK/PBI membranes were twice that of Nafion 117 at 60 °C. This membrane maintained high power densities for more than 50 days of operation and therefore is seen as a potential candidate for portable DMFC applications [89]. 

Figure 20. Electro-osmotic drag coefficients of diverse membranes based on perfluorinated polymers (Dow - and Nafion/silica composites ) and polyarylenes (S—PEK/ PSU blends, ionically cross-linked S—PEK/PBP ), as a function of the solvent (water/methanol) volume fraction Xy (see text for references). Lines represent data for Nafion and S—PEK (given for comparison) for data points, see Figure 15. Dashed lines correspond to the maximum possible electro-osmotic drag coefficients for water and methanol, as indicated (see text).

Reagents. Choline oxidase and glucose oxidase and their respective substrates, choline chloride and glucose were purchased from Sigma Chemical Co. (St.Louis, USA). The cationic exchangers AQ 29D and 55D were kindly supplied by Eastman Chemical Inc. (Kingsport, USA) and were obtained as dispersed polymer solutions at concentration of 30 and 28% (w/v) in water, respectively. A blend of the AQ polymer solutions was prepared by mixing the AQ 29D with the AQ 55D in a ratio (1 1), and was further diluted with water to a final concentration % (w/v) indicated in the text. Nafion (equivalent mass 1100 g) 5% (w/v) in a mixture of lower aliphatic alcohols and 10% of water was obtained from Aldrich (St.Louis, USA) and diluted with methanol to yield a stock solution of 0.5% (w/v). 

They exhibit excellent thermal and mechanical properties, enhanced chemical stability and conductivities similar to Nafion ( 0.08 S cm-1 at 30 °C). Blending of these polymers with heteropolyacids... 

Many approaches have been developed for the production of ionic liquid-polymer composite membranes. For example, Doyle et al. [165] prepared RTILs/PFSA composite membranes by swelling the Nafion with ionic liquids. When 1-butyl, 3-methyl imidazolium trifluoromethane sulfonate was used as the ionic liquid, the ionic conductivity ofthe composite membrane exceeded 0.1 S cm at 180 °C. A comparison between the ionic liquid-swollen membrane and the liquid itself indicated substantial proton mobility in these composites. Fuller et al. [166] prepared ionic liquid-polymer gel electrolytes by blending hydrophilic RTILs into a poly(vinylidene fiuoridej-hexafluoropropylene copolymer [PVdF(HFP)] matrix. The gel electrolytes prepared with an ionic liquid PVdF(HFP) mass ratio of 2 1 exhibited ionic conductivities >10 Scm at room temperature, and >10 Scm at 100 °C. When Noda and Watanabe [167] investigated the in situ polymerization of vinyl monomers in the RTILs, they produced suitable vinyl monomers that provided transparent, mechanically strong and highly conductive polymer electrolyte films. As an example, a 2-hydroxyethyl methacrylate network polymer in which BPBF4 was dissolved exhibited an ionic conductivity of 10 S cm at 30 °C. 

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