Structure-Relaxation Interplay of a New Nanostructured Membrane Based on Tetraethylammonium Trifluoromethanesulfonate Ionic Liquid and Neutralized Nafion 117 for High-Temperature Fuel Cells

Abstract

In this report, the electrical performance at T > 100 degrees C and low relative humidity of proton-conducting Nafion-based membranes was improved by preparing new materials based on Nafion 117 (N117) neutralized with triethylammonium (TEA(+)) and doped with the ionic liquid (IL) trifluoromethanesulfonate of triethylammonium (TEA-TF). In particular, a new two-step protocol for the preparation of [N117(x-)(TEA(+))(x)/(TEA-TF)(y)] is proposed. [N117(x-)(TEA(+))(x)/(TEA-TF)(y)] membrane is composed of ca. 30 wt % of TEA-TF. The structure of the different nanophases composing the materials and their interactions were investigated by FT-IR ATR and micro-Raman spectroscopy. The thermal stability, water uptake, and mechanical properties of the membranes were studied by thermogravimetric analysis and dynamic mechanical analysis measurements. With respect to pristine N117, the thermal and mechanical properties of the proposed materials were improved. The electric response of [N117(x-)(TEA(+))(x)/(TEA-TF)(y)] was studied by broad band dielectric spectroscopy in the frequency range from 10(-2) Hz to 10 MHz and for temperatures between 5 and 155 degrees C. In comparison to the N117 reference, the following was observed: (a) the stability range of conductivity (SRC) of the [N117(x-)(TEA(+))(x)] membrane increases up to 155 degrees C, while its sigma(DC) at T = 100 degrees C is lowered by ca. 2 orders of magnitude; (b) the SRC of [N117(x-)(TEA(+))(x)/(TEA-TF)(y)] is similar to that of [N117(x-)(TEA(+))(x)], while the sigma(DC) at 145 degrees C decreases in the order 7.3 x 10(-3) > 6.1 x 10(-3) > 9.7 x 10(-4) S x cm(-1) for [N117(x-)(TEA(+))(x)/(TEA-TF)(y)], N117, and [N117(x-)(TEA(+))(x)] membranes, respectively. In conclusion, the lower water uptake, the improved thermal and mechanical stability, and the good conductivity make [N117(x-)(TEA(+))(x)/(TEA-TF)(y)] a promising membrane to improve for application in proton exchange membrane fuel cells operating under anhydrous conditions at T > 100 degrees C.

Improving the Conductivity of Sulfonated Polyimides as Proton Exchange Membranes by Doping of a Protic Ionic Liquid

“…It provides a lower melting point (64.3 °C) and led to better ionomer-PIL interactions, which plays a major role in determining the conductivity of the IL-doped SPI membranes [31]. Conductivities of membranes in anhydrous atmosphere depended on temperature, ionic liquid concentration in the membrane, the type of polymer matrix [16] and the possible interactions between ILs and polymers [21,32]. Figure 4 shows the Arrhenius plot for the temperature-dependent conductivities, which shows that the SPI/IL composites deviated slightly from Arrhenius-like behavior.…”

“…Not only have these hydrocarbon-based membranes and inorganic composite membranes been explored, but also the application of protic ionic liquid (PIL) doped into those hydrocarbon-based membranes has been recently studied to promote the performance of PEM above 100 °C [13][14][15][16][17][18][19][20]. Noto et al improved the Nafion-based membranes by preparing new materials based on Nafion 117 neutralized with triethylamine (TEA) and doped with the ionic liquids (ILs), triethylammonium trifluoromethanesulfonate [21], triethylammonium methanesulfonate and triethylammonium perfluorobutane sulfonate [22,23].…”

Electrochemical and structural characterization of sulfonated polysulfone

“…Currently, perfluorosulfonated polymer electrolytes, such as Nafion ® from Dupont or Aquivion ® from Sol vay, are the most widely used electrolytes in PEMFCs due to their high proton conductivity, mechanical properties up to 80 C and chemical and electrochemical stability. However, this type of membrane also exhibits some drawbacks, which are primarily high cost, low stability at high temperatures, low conductivity at low humidity or high temperature and high methanol crossover in direct methanol fuel cells (DMFCs) [2]. Therefore, extensive studies have been focused on developing alternatives to these per fluorosulfonated membranes [3].…”

Agarose processing in protic and mixed protic–aprotic ionic liquids: dissolution, regeneration and high conductivity, high strength ionogels

“…[32][33][34][35][36][37][38][39][40][41][42][43][44][45] Ionogels can be obtained by hybridizing ILs with low molecular weight organic gelators, inorganics (e.g. carbon nanotubes, silica, etc.…”