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Polymers based on ionic conducting materials have important interest because of their potential applications in polymer electrolytes and membranes for fuel cell application. PVdF-co-HFP poly(viniliden-co-hexafluoropropylene) was chosen as a polymer matrix because of its high ionic conductivity and better mechanical properties. Polymer matrix composites were prepared with various amounts of LiClO4 salt by a solution casting method. The sample-ionic conductivity measurements were recorded by AC impedance analyzer at different frequencies from 0.1 Hz to 20 MHz and at different temperatures from 273 to 373 K. The changes of nanoscopic free volume and free volume fraction in these materials were investigated in terms of temperature from 273 to 373 K using Positron Annihilation Lifetime Spectroscopy (PALS) and Simha-Somcynsky (SS) Hole Theory. The free volume had a bump at about 3% in weight percentage of the salt and there is a slight increase after 10%. The effects of weight percentages of LiClO4 and temperature were investigated. The mechanism of the ac ionic conductivity was presented in terms of the free volume models, however thermo-occupancy function justifies the best accurate representation of the data. [ABSTRACT FROM AUTHOR]

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The paper deals with the synthesis and characterization of a new series of anhydrous conducting acid-doped complex membranes based on polyimide (PI) and ionic liquid (IL) for high-temperature fuel cells via a new route. For this purpose, three imidazolium-based ILs (RIm+BF4−) with different alkyl chain lengths (R=methyl, ethyl, and butyl) are added into polyamic acid (PAA) intermediate prepared from the reaction of benzophenonetetracarboxylic dianhydride and diaminodiphenylsulfone in different -COOH/imidazolium molar ratios ( n = 0.5, 1, and 2). Then, the thermally imidized complex membrane was doped with H2SO4. The conductivities of acid-doped PI/IL complex membranes prepared by taking n of 1 are found to be in the range of 10−4−10−5 S cm−1 at 180°C, whereas the acid-free PI/IL complex membranes show the conductivity at around 10−9−10−10 S cm−1. Thermogravimetric analysis results reveal that the acid-doped PI/IL complex membranes are thermally stable up to 250°C. Dynamic mechanical analysis results of the acid-doped ionically interacted complex membrane show that the mechanical strengths of the PI/IL complex membranes including 1-methyl imidazolium tetrafluoroborate (MeIm-BF4) and 1-ethyl 3-methyl imidazolium tetrafluoroborate (EtIm-BF4) are comparable with those of pristine PI until 200°C. Furthermore, it can be clearly emphasized that the ionic interaction between carboxylic acid groups of PAA's and IL's cations offers a positive role in long-term conductivity stability by preventing the IL migration at high temperatures. On the other hand, preliminary methanol permeability tests of the acid-doped membranes show that they can also be considered as an alternative for direct methanol fuel cells. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Highly proton conductive and mechanically stable Nafion®112 based composite membranes with suppressed methanol permeability were prepared via Layer-by-Layer (LbL) technique for fuel cell applications. It was observed from UV–vis results that the polyelectrolyte layers growth on Nafion membrane surface regularly. (PAH/PSS)20–H+ with 0.01M NaCl exhibited 39.9% reduction in methanol permittivity and nearly 2 times higher proton conductivity (0.152Scm−1) than that of untreated Nafion®112. Promisingly, it was found that the membrane selectivity (Φ) values of all multilayered composite membranes in proton form prepared from polyelectrolytes comprising NaCl were higher than that of both untreated and chemically treated Nafion®112. Furthermore, the mechanical and thermal properties of the composite membrane obtained from polyelectrolytes free salt were enhanced due to the interaction between the polar phase of Nafion and anionic/cationic charges of polyions. [Copyright &y& Elsevier]