Preparation and characterization of ammonium-functionalized polysulfone/Al₂O₃ composite membranes

In the current study, a quaternary ammonium polysulfone/Al₂O₃ composite anion exchange membrane was prepared. This membrane was synthesized using different Al₂O₃ powder loadings (1–4 wt%) and a casting procedure to avoid the use of hazardous materials. The ammonium-functionalized polysulfones were characterized using ¹H NMR and FTIR analyses, and the presence of Al₂O₃ in the polymeric matrix was confirmed by EDS. The resulting composite membranes exhibited high thermal stability for typical fuel cell operation temperatures below 100 °C. The presence of Al₂O₃ increased the water absorption and the ion exchange capacity of the membranes. The ionic conductivity of the membranes in dilute aqueous solutions of potassium hydroxide (10⁻⁴–10⁻¹ M) was studied using impedance spectroscopy. The results indicated that the ionic conductivity was twice as high when a loading of 4 % Al₂O₃ was added. The activation energies for ionic transport ranged from 58 to 63 kJ mol⁻¹. The introduction of Al₂O₃ significantly increased the mechanical strength but decreased the elongation at break, indicating an interaction between the inorganic nanoparticles and the polymer. Therefore, these results suggest that these composite membranes have the potential for use as solid anion exchange electrolytes in low temperature fuel cells.