Bipolar-parallel-plate gas-flow channels for proton-exchange-membrane fuel cells (PEMFCs) with serpentine, grid, and branch gas-flow channel configurations were prepared from various composites of nylon-6 and carbon black (CB). The effect of temperature on the resistivity of the nylon-6/CB composite was examined, and their voltage-current curves and power density-current curves in PEMFCs were analysed. Although the injection-moulding process has many advantages, including the potential for automated production, a short cycle time, precise tolerances, the plates produced cannot operate at temperatures above 120 deg.C and lead to a poor conductivity in the PEM fuel - cell stack. 19 refs.

The synthesis, characterisation and hydrolysis of poly(vinylidene fluoride-ter-perfluoro(4-methyl-3,6-dioxaoct-7-ene) sulphonyl fluoride-ter-8-bromo-1H,1H,2H-perfluorooct-1-ene) terpolymers followed by the crosslinking of the hydrolysed materials is described. The physicochemical, thermal and electrochemical properties of the resulting materials are discussed. 60 refs.

The synthesis of an amorphous, organosoluble, fluorine-containing polybenzimidazole (PBI) is described. Proton conducting PBI membranes are prepared by solution casting and doped with different amounts of phosphoric acid. Membranes show better methanol barrier ability than a Nafion membrane. The proton conductivity increases with temperature and phosphoric acid concentration. At higher temperatures proton conductivity is better than in Nafion 117 membranes. 18 refs.

Polypyrrole coatings were prepared on stainless steel SS304 in order to study the corrosion protection provided by the conductive polymer in a simulated PEM fuel cell environment. The polypyrrole was deposited by electrochemical polymerisation with 0.04, 0.07 and 0.14gcm - 2 onto SS304 electrodes. Polarisation curves, taken after immersion for 1, 3 or 24h in 0.1M sulphuric acid at either room temperature or 60 deg.C were used as an accelerated test. For short immersion times, it was found that corrosion current densities (at free corrosion potentials), diminished up to 2 orders of magnitude for samples tested at room temperature and up to 4 orders of magnitude for samples tested at 60 deg.C. Furthermore, at potentials in the range of the PEM fuel cell anode potential, corrosion rates also decreased up to several orders of magnitude. However, these protective properties were lost at longer times of immersion. The addition of DBSA to the polypyrrole coatings did lead to improved corrosion current densities at the free corrosion potential, however due to the loss of passivity of these samples, the corrosion rates in the potential range applicable to PEM fuel cells were either similar to or larger than bare metal. SEM was used to determine the morphology of the coatings and showed that the most homogeneous coating was obtained for 0.07gcm - 2 polypyrrole, without the incorporation of DBSA. 13 refs.

To develop a highly chemically stable polymer electrolyte membrane for application in a direct methanol fuel cell (DMFC), doubly crosslinked membranes were prepared by chemical crosslinking using bifunctional monomers, such as divinylbenzene (DVB) and bis(p,p-vinyl phenyl) ethane (BVPE), and by radiation crosslinking. The membranes were prepared by grafting of m,p-methylstyrene (MeSt) and p-tert-butylstyrene (tBuSt) into poly(ethylene-co-tetrafluoroethylene) (ETFE) films and subsequent sulphonation. The effects of the DVB and BVPE crosslinkers on the grafting kinetics and the properties of the prepared membranes, such as water uptake, proton conductivity and chemical stability were investigated. Radiation crosslinking was introduced by irradiation of the ETFE base film, the grafted film or the sulphonated membrane. The membrane crosslinked by DVB and BVPE crosslinkers and post-crosslinked by gamma-ray irradiation of the corresponding grafted film possessed the highest chemical stability among the prepared membranes, a significantly lower methanol permeability compared to Nafion (R) membranes, and a better DMFC performance for high methanol feed concentration. Therefore, this doubly crosslinked membrane was promising for application in a DMFC where relatively high methanol concentration could be fed. 24 refs.

Radiation grafting is a well-established technique for the preparation of polymer electrolyte membranes for fuel cells . The nature of the base films is an important parameter which is in close relation to the properties of the fuel cell membranes. In this study, six commercially available fluoropolymer films, PTFE, FEP, PFA, ETFE, PVDF and PVF films, together with the crosslinked PTFE (cPTFE) films have been studied with respect to their suitability for the preparation of fuel cell membranes. The PTFE and PVF films are not suitable for the preparation of fuel cell membranes. The former is quite unstable for radiation and the latter undergoes only surface grafting. The FEP-based membrane shows the highest proton conductivity over the entire ion exchange capacity range and the lowest water uptake over the entire conductivity range, while the ETFE-based membrane shows the opposite results. Perfluorinated film-based membranes are considerably more chemically stable than the partially fluorinated film-based membranes. However, the latter shows a significantly better mechanical property than the former. It is concluded that the perfluorinated film-based membranes are promising materials for the hydrogen-fed fuel cells , and the partially fluorinated film-based membranes are appropriate for the liquid methanol-fed fuel cells . 35 refs. Copyright (c) 2006 Elsevier B.V.

Polybenzimidazole (PBI) membranes have been prepared with different molecular weights. The water and acid swelling, mechanical strength, gas permeability and proton conductivity were studied for the pristine and acid doped PBI membranes. When doped with 5 mol of phosphoric acid per mole repeat unit of the polymer, a level necessary to obtain high enough proton conductivity for fuel cell uses, the polymer membrane exhibits a volume swelling by 118%, resulting in separation of the polymer backbones. The separation in turn reduces the mechanical strength of the membrane especially at high temperatures. Another consequence is the increased H"2 and O"2 permeability through the membrane. In the temperature range from 120 to 180 deg.C, the hydrogen permeability was found to be 1.6-4.3x10 - 1 7 and 1.2-4.0x10 - 1 5 molcmcm - 2s - 1Pa - 1 for pristine and acid doped PBI membranes, respectively, while for oxygen it was 5.0-10x10 - 1 9 and 3.0-9.4x10 - 1 6 molcmcm - 2s - 1Pa - 1, respectively. High molecular weights of the polymers improve the mechanical strength but have little influence on the proton conductivity of the membranes. 35 refs. Copyright (c) 2006 Elsevier B.V.

A great deal of effort is required to design polymer electrolyte fuel cells (PEFCs) using new polymers and hybrid organic/inorganic compounds that can work at higher temperatures. These materials must have lasting thermal stability as well as improved ionic conductivity. Operation at elevated temperatures is desirable for PEFCs systems since they draw high power density in fast electrode kinetics and also for improvement of CO-tolerance, etc. In the higher range of temperatures (150-200 deg.C), new materials such as solid acids with phase transition to superprotonic conduction or strong solid acids supported on metal oxide systems seem to be an appropriate alternative to polybenzimidazoles (PBI) and other composite membranes. In this context, we evaluate a new hybrid matrix resistant at high temperatures, made of pyridine polymer obtained from polyacrylonitrile (PAN) and nanometric oxides (e.g., zirconium(IV) oxide-yttria stabilised, YSZ) by thermo-oxidative process in a centrifugal field. These hybrid matrixes aim further developments either to embed solid acids nanoparticles or to design strong solid acids on nanooxides, making them appropriate for proton exchange membranes. SEM, TEM, XRD and Raman spectroscopy were used to establish the structure and morphology and to characterize the composite membranes. The dependence of the electrical conductivity on temperature, water uptake, and methanol permeability are evaluated. 29 refs. Copyright (c) 2006 Elsevier B.V.

Polymer blends of sulphonated poly(ether ether ketone) (SPEEK) and poly(ether sulphone) (PES) in N-methyl-2-pyrrolidinone (NMP) were prepared by solution casting. The investigation on water uptake, methanol uptake, permeability and proton conductivity has been conducted. The spin-lattice relaxation time in the rotating frame (T"1"rho H) of PES/SPEEK blend was obtained from the results of cross-polarisation magic angle spinning (CP/MAS) solid state 1 3C NMR. SPEEK blended with PES resulted in increasing T"1"rho H, indicating the molecular motion of polymer chain was reduced. The glass transition temperatures of the PES/SPEEK blend membranes were predicted by the Kwei equation. PES plays an important role in the decreasing water uptake, methanol uptake and methanol permeability while enhancing the thermal stability of the blend membrane, which shows the feasibility for direct methanol fuel cell . 36 refs.

A complete physicochemical characterisation of two ion-exchange membranes-CM2 and Nafion (R)117-used in electrodialysis and in direct methanol fuel cells (DMFC) has been carried out. For each membrane, in different methanol-water mixtures-0%, 20%, 40%, 60%, 80% and 100%-and at different temperatures (25.0; 40.0 and 55.0 deg.C), we have measured the variations of the geometrical dimensions, the proton electrical conductivity, the swelling rate and the amount of methanol in the membrane. The FTIR analysis of Nafion (R)117 was performed at different methanol contents of the external solution. The results show that the CM2 membrane presents the best geometrical stability, and the lowest conductivity at any methanol content. At high methanol contents, Nafion (R)117 is 10 times more conductive than the CM2 membrane. It was found that the methanol is absorbed more by Nafion (R)117, and its effect is more noticeable on the microstructure of this membrane, under standard conditions. The high methanol permeability of these membranes, particularly of the Nafion (R)117, induces bad cell efficiencies and lifetimes. 21 refs. Copyright (c) 2006 Elsevier Ltd.