The preparation and characterization of composite polybenzimidazole (PBI) membranes containing zeolitic imidazolate framework 8 (ZIF-8) and zeolitic imidazolate framework 67 (ZIF-67) is reported. The phosphoric acid doped composite membranes display proton conductivity values that increase with increasing temperatures, maintaining their conductivity under anhydrous conditions. The addition of ZIF to the polymeric matrix enhances proton transport relative to the values observed for PBI and ZIFs alone. For example, the proton conductivity of PBI@ZIF-8 reaches 3.1 × 10⁻³ S·cm⁻¹ at 200 °C and higher values were obtained for PBI@ZIF-67 membranes, with proton conductivities up to 4.1 × 10⁻² S·cm⁻¹. Interestingly, a composite membrane containing a 5 wt.% binary mixture of ZIF-8 and ZIF-67 yielded a proton conductivity of 9.2 × 10⁻² S·cm⁻¹, showing a synergistic effect on the proton conductivity.

A series of proton exchange membranes based on polybenzimidazole (PBI) were prepared using the low cost ionic liquids (ILs) derived from 1-butyl-3-methylimidazolium (BMIM) bearing different anions as conductive fillers in the polymeric matrix with the aim of enhancing the proton conductivity of PBI membranes. The composite membranes prepared by casting method (containing 5 wt. % of IL) exhibited good thermal, dimensional, mechanical, and oxidative stability for fuel cell applications. The effects of anion, temperature on the proton conductivity of phosphoric acid-doped membranes were systematically investigated by electrochemical impedance spectroscopy. The PBI composite membranes containing 1-butyl-3-methylimidazolium-derived ionic liquids exhibited high proton conductivity of 0.098 S·cm⁻¹ at 120 °C when tetrafluoroborate anion was present in the polymeric matrix. This conductivity enhancement might be attributed to the formed hydrogen-bond networks between the IL molecules and the phosphoric acid molecules distributed along the polymeric matrix.

A series of novel composite membranes, based on sulfonated poly(ether ketone) (SPEEK) with a graphene oxide (GO) layer, were prepared. One contained a GO layer sandwiched between the SPEEK–polyvinyl alcohol (PVA) matrix (SPEEK/PVA@GO), and another deposited thin layers of GO on the nanofibers of SPEEK–polyvinyl butyral (PVB), with both sandwiched in the phase matrix of SPEEK–PVA (SPEEK/PVA@GO-NF). Various nanofiber thicknesses were studied by varying the electrospinning time. The prepared composite membranes with different nanofiber thicknesses were characterized by scanning electron microscopy, water uptake, ionic exchange capacity, thermogravimetric analysis, mechanical properties and proton conductivity. Our results showed that the proton conductivity of SPEEK/PVA@GO membranes increased with temperature, from 1 × 10⁻³ S cm⁻¹ at 30 °C to 8.3 × 10⁻³ S cm⁻¹ at 130 °C. These conductivity values are higher than those observed for the membrane with SPEEK/PVA@GO-NF nanofibers. However, a conductivity comparison of the different thicknesses of SPEEK/PVA@GO-NF nanofibers allowed us to conclude that conductivities increase with nanofiber thickness at all temperatures. Finally, the calculated activation energy of the SPEEK/PVA@GO membrane (1.4 kJ mol⁻¹) was found to be one order of magnitude lower than that for pure SPEEK/PVA (17.3 kJ mol⁻¹). This reduction indicated that the influence of temperature on the conductivity decreases when GO is inserted into SPEEK/PVA membranes. In the case of the SPEEK/PVA@GO-NF membrane, the activation energy decreased as a function of the nanofiber network's thickness.