Thickness effect on mechanical propierties and water lcohol uptake in direct ethanol fuel cells membranes

Abstract

he mechanical properties of polybezimidazole (PBI) or modified PBI membranes, possible candidates to replace Nafion as proton exchange membranes in direct methanol fuel cells (DMFC) were studied. Phosphoric acid-doped membranes based in poly [2,5- benzimidazole] (ABPBI) were obtained by high temperature casting from methanesulphonic acid and by a new low temperature casting procedure. These membranes were studied in relation with their phosphoric acid doping level by measuring the free and bonded acid. The elastic moduli of these membranes, doped and undoped, were determined using the force spectroscopy AFM technique and compared with those determined for doped and undoped PBI (poly [2-2´-(m-fenylene)-5-5´ bibenzimidazole]) and for Nafion membranes. The water isotherms were also determined for the low and high temperature casted ABPBI membranes. It is found that a simple empirical isoterm described the water sorption of these membranes all over the water activity range (0.15 < aw < 1).