Fabrication of new proton conducting membrane for fuel cell applications based on porous polyimide Matrimid® and hydrophobic protic ionic liquid

Abstract

A new proton conducting membrane has been developed by impregnation of porous polyimide Matrimid® (PI) with hydrophobic protic ionic liquid triethylammonium bis(trifluoromethylsulfonyl)imide (TEA‐TFSI). According to the results of dynamic mechanical analysis (DMA), PI/TEA‐TFSI membrane has satisfactory viscoelastic properties in the temperature range 25–100°C. However, the sharp drop in storage modulus (E') occurs at higher temperatures that is probably caused by the plasticizing effect of ionic liquid. To improve the mechanical properties of PI matrix, it was impregnated with the solution of polyetheramine Jeffamine® D‐400 in the TEA‐TFSI. This approach allowed to obtain a partially cross‐linked PI which is more resistant to deformation at elevated temperatures. Thus, DMA study revealed a storage modulus around 400 MPa for PI/Jeffamine/TEA‐TFSI membrane up to 150°C, like neat porous Matrimid®. Thermogravimetric analysis results indicate high thermal stability of PI/Jeffamine/TEA‐TFSI composite with thermal degradation point of 343°C. The ionic conductivity of the composite membrane is 4·10−3 S/cm at room temperature and reaches the level of 10−2 S/cm above 100°C. Overall, the results of this study indicate that partially cross‐linked porous PI impregnated with hydrophobic protic ionic liquid is a promising polymer electrolyte membrane for fuel cells operating at elevated temperatures in water‐free conditions.