Nanocomposite Membranes based on Polybenzimidazole and ZrO2 for High-Temperature Proton Exchange Membrane Fuel Cells

Owing to the numerous benefits obtained when operating proton exchange membrane fuel cells at elevated temperature (>100 °C), the development of thermally stable proton exchange membranes that demonstrate conductivity under anhydrous conditions remains a significant goal for fuel cell technology. This paper presents composite membranes consisting of poly[2,2?-(m-phenylene)-5,5?-bibenzimidazole] (PBI4N) impregnated with a ZrO<inf>2</inf> nanofiller of varying content (ranging from 0 to 22 wt %). The structure-property relationships of the acid-doped and undoped composite membranes have been studied using thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, wide-angle X-ray scattering, infrared spectroscopy, and broadband electrical spectroscopy. Results indicate that the level of nanofiller has a significant effect on the membrane properties. From 0 to 8 wt %, the acid uptake as well as the thermal and mechanical properties of the membrane increase. As the nanofiller level is increased from 8 to 22 wt % the opposite effect is observed. At 185 °C, the ionic conductivity of [PBI4N(ZrO<inf>2</inf>)<inf>0.231</inf>](H<inf>3</inf>PO<inf>4</inf>)<inf>13</inf> is found to be 1.04×10^-1 S cm^-1. This renders membranes of this type promising candidates for use in high-temperature proton exchange membrane fuel cells.