New polymer electrolyte membrane for medium-temperature fuel cell applications based on cross-linked polyimide Matrimid and hydrophobic protic ionic liquid
Résumé
New hydrophobic protic ionic liquid, 2-butylaminoimidazolinium bis(trifluoromethylsulfonyl)imide
(BAIM-TFSI), has been synthesized. The ionic liquid showed good thermal stability to at least 350 C. The
conductivity of BAIM-TFSI determined by electrochemical impedance method was found to be
5.6 102 S/cm at 140 C. Homogeneous composite films based on commercial polyimide (PI)
Matrimid and BAIM-TFSI containing 30e60 wt% of ionic liquid were prepared by casting from methylene
chloride solutions. Thermogravimetric analysis data indicated an excellent thermal stability of PI/BAIMTFSI composites and thermal degradation points in the temperature range 377 Ce397 C. The addition of
ionic liquid up to 50 wt% in PI films does not lead to any significant deterioration of the tensile strength of
the polymer. The dynamic mechanical analysis results indicated both an increase of storage modulus E0 of
PI/BAIM-TFSI composites at room temperature and a significant E0 decrease with temperature compared
with the neat polymer. The cross-linking of the PI with polyetheramine Jeffamine D-400 allowed to
prepare PI/Jeffamine/BAIM-TFSI (50%) membrane with E0 value of 300 MPa at 130 C. The ionic conductivity of this cross-linked composite membrane reached the level of 102 S/cm at 130 C, suggesting,
therefore, its potential use in medium-temperature fuel cells operating in water-free conditions.
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