1-butyl-3-methylimidazolium sulfate (BMI.HSO4), 1-butylimidazole sulfate (BImH.HSO4) and 3-triethylammonium hydrogen sulfate (TEA-PS.HSO4) ionic liquids were encapsulated in UiO-66 (Zr-MOF) framework. These materials were incorporated into sulfonated poly(ether ether ketone) (SPEEK) membranes in different concentrations of ionic liquid. The influence of ionic liquid concentration encapsulated in Zr-MOF was evaluated through the morphology and thermal and chemical stability of the modified membranes. The incorporation of 7.5 wt.% Zr-MOF in SPEEK produced membranes with high proton conductivity, making this the best mass ratio for the incorporation of the ionic liquids. Contact angle and swelling analysis indicate that the presence of these ionic liquids provides stability to the membrane, preventing it from absorbing high amounts of water. Mass ratios of 2.5 and 5.0 wt.% of encapsulated ILs in Zr-MOF were also used. Proton conductivity results show that a higher concentration of ionic liquid generates agglomerates, limiting proton mobility in the membranes. Among the three ionic liquids tested, TEA-PS.HSO4 presents the best proton conductivity values, between 92 and 140 mS cm-1. These results indicate a possible application in proton exchange membrane fuel cells (PEMFCs).
Summary
Nafion membranes were prepared by incorporating in the polymer matrix the 1‐butyl‐3‐methylimidazolium (BMI+) ionic liquid cation at different doping levels. Increasing the doping time of the membranes with the ionic liquid results in increased incorporation of the BMI+ cation but a decrease in the bulk conductivity. The thermogravimetric analysis shows that the BMI+ cation incorporation increases the thermal stability of the membranes. The higher discharge efficiency of the fuel cell at 80°C was obtained by using Nafion membrane after 15 minutes of doping in the ionic liquid solution.
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