Effect of composition on the properties of PEM based on polybenzimidazole and poly(vinylidene fluoride) blends

Abstract

Inadequate performance, short term durability and high cost of polymer electrolyte membrane (PEM) are the major roadblocks that need to be resolved for successful commercialization of high temperature PEM fuel cell. In this report, we investigated the viability of previously developed miscible blend membranes of polybenzimidazole and poly (vinylidene fluoride) (PBI/PVDF), as potential PEMs. In addition, we have carried out several advanced analytical techniques such as dynamic mechanical analysis (DMA), 13C CP-MAS solid state NMR (SS-NMR) and wide-angle X-Ray diffraction (WAXD) to prove the miscible behavior of the polymer pair. Sub-ambient temperature DMA studies confirmed the miscible behavior of PBI/PVDF blends at different compositions based on single Tg criterion. SS-NMR and WAXD showed the presence of interactions between the functional groups of the polymers and their dependence on blend composition. Thermogravimetric analysis of phosphoric acid (PA) doped and undoped blend membranes confirmed the improved thermal stability of the membranes compared to neat PBI. The membranes exhibited excellent oxidative stability than pristine PBI membrane. The swelling ratio and volume after dipping in PA was found to be significantly low in the blend membranes owing to the hydrophobic nature of PVDF. Among the blends prepared, 90/10 and 75/25 membranes showed higher proton conductivity than PBI, attributed in part, to electronegativity of fluorine and crystallinity of PBI in PA that activate proton transport. The results demonstrated the potential usefulness of the blend membranes as PEM in fuel cell.