Fabrication of protic ionic liquid/sulfonated polyimide composite membranes for non-humidified fuel cells

We have demonstrated that a protic ionic liquid, diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]) functions as a proton conductor and is suitable for use as an electrolyte in H-2/O-2 fuel cells, which can be operated at temperatures higher than 100 degrees C under non-humidified conditions. In this study, in order to fabricate a polymer electrolyte fuel cell, matrix polymers for [dema][TfO] are explored and sulfonated polyimides (SPI), in which the sulfonic acid groups are in diethylmethylammonium form, are found to be highly compatible with [dema][TfO]. Polymer electrolyte membranes for non-humidified fuel cells are prepared by the solvent casting method using SPI and [dema][TfO]. The SPI, with an ion exchange capacity of 2.27 meq g(-1), can retain four times its own weight of [dema][TfO] and produces uniform, tough, and transparent composite membranes. The composite membranes have good thermal stability (>300 degrees C) and ionic conductivity (>10(-2) S cm(-1) at 120 degrees C when the [dema][TfO] content is higher than 67 wt%) under anhydrous conditions. In the H-2/O-2 fuel cell operation using a composite membrane without humidification, a current density higher than 240 mA cm(-2) is achieved with a maximum power density of 100 mW cm(-2) at 80 degrees C. (C) 2009 Elsevier B.V. All rights reserved.