Abstract
In this work, the design and characterization of new supported ionic liquid membranes, as medium-temperature polymer electrolyte membranes for fuel-cell application, are described. These membranes were elaborated by the impregnation of porous polyimide Matrimid® with different synthesized protic ionic liquids containing polymerizable vinyl, allyl, or methacrylate groups. The ionic liquid polymerization was optimized in terms of the nature of the used (photo)initiator, its quantity, and reaction duration. The mechanical and thermal properties, as well as the proton conductivities of the supported ionic liquid membranes were analyzed in dynamic and static modes, as a function of the chemical structure of the protic ionic liquid. The obtained membranes were found to be flexible with Young’s modulus and elongation at break values were equal to 1371 MPa and 271%, respectively. Besides, these membranes exhibited high thermal stability with initial decomposition temperatures > 300 °C. In addition, the resulting supported membranes possessed good proton conductivity over a wide temperature range (from 30 to 150 °C). For example, the three-component Matrimid®/vinylimidazolium/polyvinylimidazolium trifluoromethane sulfonate membrane showed the highest proton conductivity—~5 × 10−2 mS/cm and ~0.1 mS/cm at 100 °C and 150 °C, respectively. This result makes the obtained membranes attractive for medium-temperature fuel-cell application.
Highlights
The implementation of renewable eco-friendly energy sources, such as solar, wind, and hydropower, over fossil fuels is progressively gaining momentum
It has been shown that using nonaqueous proton carriers, instead of water, is a simple and effective method of obtaining polymer electrolyte membranes with a high proton conductivity at temperatures higher than 100 ◦C [18]
protic ionic liquids (PILs) have attracted much attention as proton carriers, as they can be used at temperatures above 100 ◦C under anhydrous conditions without conductivity decreases due to their negligible volatility and excellent thermal stability
Summary
The implementation of renewable eco-friendly energy sources, such as solar, wind, and hydropower, over fossil fuels is progressively gaining momentum. Polymer exchange membrane fuel cells (PEMFCs) that can operate at high temperatures (above 100 ◦C) without additional humidification are promising conductive systems for future energy technology due to their efficiency and eco-friendly nature [2,3]. PILs are insensitive to the presence of water and other proton substances, they have a low melting point, low viscosity, and high thermal and chemical stability, which is very important for their use in electrochemical processes [19,20] This fact distinguishes PILs from other types of ILs and can be used to form a hydrogen-bonded network [18]. The membrane was taken from the solution and gently scraped to remove the excess of PIL from its surface, left in the air for 2 h and vacuum dried at 80 ◦C during 24 h. All prepared SILMs were stored under vacuum and dried at 80 ◦C just before characterization
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