Polyimide/ionic liquid composite membranes for fuel cells operating at high temperatures

Abstract

Supported ionic liquid membranes (SILMs) were prepared by impregnating a porous Matrimid® membrane with protic room-temperature ionic liquids (RTILs): 1-n-methylimidazolium dibutylphosphate ([C1im][DBP]), 1-n-butylimidazolium dibutylphosphate ([C4im][DBP]) and 1-n-butylimidazolium bis(2-ethylhexyl)phosphate ([C4im][BEHP]). After immersion of the porous Matrimid® membrane in each RTIL, the prepared SILMs were composed of 53±3% of RTIL phase. The control of the full impregnation of the porous Matrimid® membrane by the RTILs was verified by FTIR spectroscopy. From the bubble point test, the SILMs displayed a good retention of their RTIL phase and, thus, showed a good stability against the increased pressure on one of the faces.The ionic conductivity of SILMs, used as electrolyte membranes for proton exchange membrane fuel cell (PEMFC) was measured by impedance spectroscopy. Unlike the Nafion®, the conductivity of the SILMs still increases at high temperatures (> 80°C). The [C4im][DBP]-impregnated SILM showed the best result in terms of conductivity (2.0 10−2 S/cm at 115°C). Moreover, all SILMs showed satisfactory stability since they retained a large amount of the RTIL phase in the membrane pores.