Acid-Base Membranes Based on Poly(1-vinylimidazole) for Fuel Cell Applications

Novel acid-base electrolyte membranes have been developed using the acid-base blending of a basic polymer poly(1-vinylimidazole) (PVIm) and an acidic polymer poly(ethylene-co-acrylic acid) (PEAA). High non-aqueous ionic conductivities of the order of 10^-2 – 10^-3 S/cm were observed for acid-base blend electrolytes over the temperature range of 30-120 ^oC and are found to be stable over the temperature range measured. The highest ionic conductivity was observed for 2-8 composition and was postulated to be due to better interaction between the acid and base sites along with better morphology. The blend electrolytes developed are found to be stable up to temperatures in excess of 450^oC, even reaching 500 ^oC for 5-5 compositions. Nano-composite acid-base blend membranes using the 2-8 composition were then developed with the subsequent addition of nano-tubular titania into the electrolyte matrix. The ionic conductivity has been found to be effected by the addition of nano-tubular phase and is higher than that obtained for the parent electrolyte. This increase in conductivity is attributed to the better morphology of the electrolytes with the addition of nano-tubular titania into the matrix as inferred from SEM studies. Nanocomposite membranes were also found to be more thermally stable than the parent membranes. The addition of acid-functionalized nanotubular titania was found to further increase the ionic conductivity of the acid- base blend membranes whilst maintaining good thermal stability.