New proton exchange membrane based on polyimide Matrimid® (PI) and hydrophobic protic ionic liquid, 1-methylimidazolium bis(trifluoromethylsulfonyl)imide (MIM-TFSI), has been prepared by casting from methylene chloride/dimethylformamide solution. Infrared analysis revealed physicochemical interactions between 1-methylimidazolium cations and imide groups of PI. The results of mechanical testing indicate significantly reduced tensile strength of PI/MIM-TFSI composite membrane compared to neat polymer. Moreover, the dynamical mechanical analysis results revealed sharp drop in storage modulus (E´) of the polymer film above 60 °C.
To improve the elastic properties of the membrane, PI was successively cross-linked with polyetheramine Jeffamine® D-2000 (10 mol. %) in methylene chloride/dimethylformamide solution, as well as in solid film at 100 °C. This approach allowed to prepare PI/Jeffamine/MIM-TFSI (70 wt. %) composite film which has an acceptable E' value of 210 MPa at 140 °C. According to thermal gravimetric analysis data, PI/Jeffamine/MIM-TFSI composite has a thermal degradation point (i.e. 5 % weight loss) of 286 °C. The ionic conductivity of PI/Jeffamine/MIM-TFSI composite membrane is around 10–4 S/cm at room temperature and reaches the minimal level of 10–3 S/cm, required for fuel cell applications, above 100 °C. Overall, the results of this study indicate that the cross-linking of polyimide Matrimid with flexible polyetheramine Jeffamine is an efficient approach for preparing dense composite membrane with high content of the protic ionic liquid. Such polymer-electrolyte membrane has the reasonable combination of good stiffness, thermal stability, and ionic conductivity and therefore is a promising candidate for use in fuel cells operating at elevated temperatures in water-free conditions.
Sridhar S., Veerapur R.S., Patil M.B., Gudasi K.B., Aminabhavi T.M. Matrimid polyimide membranes for the separation of carbon dioxide from methane. J. Appl. Polym. Sci., 2007, 106, 1585-1594.
Langevin D., Trong Nguyen Q., Marais S., Karademir S., Sanchez J.-Y., Iojoiu C., Martinez M., Mercier R., Judeinstein P., Chappey C. High-temperature ionic-conducting material: advanced structure and improved performance. J. Phys. Chem. C., 2013, 117, 15552-15561.
Fatyeyeva K., Rogalsky S., Makhno S., Tarasyuk O., Soto Puente J.A., Marais S. Polyimide/ionic liquid composite membranes for middle and high temperature fuel cell applications: water sorption behavior and proton conductivity. Membranes, 2020, 10, 82.
Rogalsky S., Bardeau J.-F., Makhno S., Tarasyuk O., Babkina N., Cherniavska T., Filonenko M., Fatyeyeva K. New polymer electrolyte membrane for medium-temperature fuel cell applications based on cross-linked polyimide Matrimid and hydrophobic protic ionic liquid. Mater. Today Chem., 2021, 20, 100453.
Diaz M., Ortiz A., Ortiz I. Progress in the use of ionic liquids as electrolyte membranes in fuel cells. J. Membrane Sci., 2014, 469, 379-396.
Susan M.A.B.H., Noda A., Mitsushima S., Watanabe M. Brønsted acid-base ionic liquids and their use as new materials for anhydrous proton conductors. Chem. Commun., 2003, 8, 938-939.
Wong C.Y., Wong W.Y., Loh K.S., Lim K.L. Protic ionic liquids as next-generation proton exchange membrane materials: current status & future perspectives. React. Funct. Polym., 2022, 171, 105160.
Lee S.-Y., Ogawa A., Kanno M., Nakamoto H., Yasuda T., Watanabe M. Nonhumidified intermediate temperature fuel cells using protic ionic liquids. J. Am. Chem. Soc., 2010, 132, 9764-9773.
Moschovi A.M., Ntais S., Dracopoulos V., Nikolakis V. Vibrational spectroscopic study of the protic ionic liquid 1-H-3-methylimidazolium bis(trifluoromethanesulfonyl)imide. Vib. Spectrosc., 2012, 63, 350-359.
Kiffer J., Fries J., Leipertz A. Experimental vibrational study of imidazolium-based ionic liquids: Raman and infrared spectra of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and 1-ethyl-3-methylimidazolium ethylsulfate. Appl. Spectrosc., 2007, 61, 1306-1311.
Kharitonov A.P., Moskvin Yu.L., Syrtsova D.A., Starov V.M., Teplyakov V.V. Direct fluorination of the polyimide Matrimid® 5218: the formation kinetics and physicochemical properties of the fluorinated layers. J. Appl. Polym. Sci., 2004, 92, 6-17.
Lee T.H., Lee B.K., Park J.S., Park J., Kang J.H., Yoo S.Y., Park I., Kim Y.-H., Park H.B. Surface modification of Matrimid® 5218 polyimide membrane with fluorine-containing diamines for efficient gas separation. Membranes, 2022, 12, 256.
Yuriar-Arredondo K., Armstrong M.R., Shan B., Zeng W., Xu W., Jiang H., Mu B. Nanofiber-based Matrimid organogel membranes for battery separator. J. Membrane Sci., 2018, 546, 158-164.
Nistor C., Shishatskiy S., Popa M., Nunes S.P. Composite membranes with cross-linked Matrimid selective layer for gas separation, Environ. Eng. Manag. J., 2008, 7(6), 653-659.
Mondal S., Soam S., Kundu P.P. Reduction of methanol crossover and improved electrical efficiency in direct methanol fuel cell by the formation of a thin layer of Nafion 117 membrane: effect of dip-coating of a blend of sulphonated PVdF-co-HFP and PBI. J. Membrane Sci., 2015, 474, 140-147.
Lufrano E., Simari C., Di Vona M.L., Nicotera I., Narducci R. How the morphology of Nafion-based membranes affects proton transport. Polymers, 2021, 13, 359.