Mixed matrix composite PEM with super proton conductivity developed from ionic liquid modified silica nanoparticle and polybenzimidazole

Phosphoric acid (PA) leaching, low proton conductivity and weak mechanical strength of the polybenzimidazole (PBI) membrane need to be improved considerably for the development of proton exchange membrane (PEM). We have addressed these issues by preparing a mixed matrix composite (MMC) membrane comprising of oxy-polybenzimidazole (OPBI) and imidazole ionic liquid modified silica (ImILSi). Imidazolium based ionic liquid was synthesized and grafted to the surface of the silica nanoparticles (SiNP) to obtain ImILSi which further blended with OPBI to obtain OPBI@ImILSi. The uniform dispersion nature of the ImILSi in the OPBI matrix and the strong H-bonded interfacial interactions between nanofillers and polymers are found to be primary reason for significant improvement of various physical properties of the MMC. TGA, DMA and stress-strain studies exhibited significant enhancement in the thermal and mechanical properties of the MMC membranes. Most importantly, due to the loading of hydrophilic ImILSi, the MMC membranes resulted higher PA loading (∼3-fold increase) which enabled the formation of facial proton transport nanochannels for their superior proton conduction under anhydrous environment and elevated temperature. For example, the OPBI@ImILSi-3% membrane showed proton conductivity value of 0.219 S cm−1 at 160 °C which is a ∼4-fold increase compared to OPBI membrane.