Direct methanol fuel cells have the potential to be a cheaper alternative to hydrogen fed fuel cells, but depend on the performance of a suitable membrane material. Generally, perfluorosulfonic acid ionomer (PFSI) membranes are quite permeable to methanol leading to methanol crossover to the oxygen cathode, and reductions in the fuel cell efficiency by means of lost fuel and depolarization of the cathode. The sorption and diffusion properties of methanol vapor in membranes of equivalent weight 860 g pol/(mole(SO 3H) were studied at different activities and at 35°-65°C. The diffusivity increased with increasing temperature and showed a maximum with concentration, similar to the case of water vapor diffusion. The effect of temperature on the methanol uptake is slight and the molar uptake of methanol, at fixed activity, is moderately lower than that of water, the main difference lying in the amount of water irreversibly attached to sulfonic sites at each temperature. The diffusivity increases with temperature and shows a maximum with concentration, similarly to what observed in the case of water vapor diffusion. The same behavior can be observed for the case of water and can be due to the elastic response of the semicrystalline matrix. This is an abstract of a paper presented at the 19th International Congress of Chemical and Process Engineering and 7th European Congress of Chemical Engineering (Prague, Czech Republic 8/28/2010-9/1/2010).
|Publication status||Published - 2010|