Preparation And Properties Of PBI/POSS/IL Composite Proton Exchange Membrane

Proton exchange membrane fuel cells(PEMFCs) are environmental friendly and effective power equipments, which have wide applications in portable and stationary power sources for its high energy conversion efficiency, environmental friendly, rapid start-up. Currently, the most widely used polymer membrane in PEMFCs is Nafion membrane by Dupont, but it has two main limitations: high cost and limited operation temperature(<100 °C) which make difficult future for PEMFC commercialization. Therefore, it is critical to develop new types of membrane materials which can work at high temperature and low humidity conditions. Polybenzimidazoles(PBIs) have motivated extensive research activities because of their excellent chemical & thermal stabilities and mechanical properties, phosphoric acid(PA) doped polybenzimidazoles membranes have excellent proton conductivities at high temperature with low humidity.In this work, we selected poly(2,5-benzimidazole)(ABPBI) which is the simplest PBIs type polymer as polymer matrix, and TriSilanolPhenyl POSS as nanofillers to modified ABPBI membrane. In addition, 1-butyl-3-methylimidazolium tetrafluoroborate([BMIM]BF4) has been filled into membrane matrix as anhydrous proton conductor. Detailed research contents were summaried as follows:1) ABPBI was synthesized by solution polymerization and ABPBI membrane was prepared by solution casting. ABPBI show good thermal stability, high water and phosphoric acid absorbility, whilst the proton conductivities of H3PO4 doped ABPBI membranes increased with the rising temperature and H3PO4 absorption.2) A series of ABPBI/SO-POSS composite membranes were synthesized in situ by using TriSilanolPhenyl POSS(SO-POSS) as fillers and poly(2,5-benzimidazole)(ABPBI) as polymer matrix. The chemical structure, thermal stabilities and morphologies of composite membrane were characterized by means of FT-IR, TGA and SEM-EDS. The water and H3PO4 absorbilities and proton conductivities of composite membranes were also investigated. Upon incorporation of SO-POSS particles, the thermal stabilities of composites are strengthened whilst the composite membranes’ water and H3PO4 absorbilities substantially increase. The proton conductivities of composite membranes which contains more bounded water are higher than ABPBI membrane with same H3PO4 doping levels, indicating that the PA doped ABPBI/SO-POSS composite membranes can be used as promising proton exchange membranes for High Temperature(HT)-PEMFCs applications.3) The ABPBI/SO-POSS-[BMIM]BF4 composite membranes were prepared by in situ method and immersing method, respectively. The effect of immersing temperature and time on the IL loading amount of the composite membrane have been evaluated. The TGA results show that the thermal stability of composite membranes reduce with the addition of IL, but still own good thermal stability which enough to be used for HT-PEMFCs. Although the IL wastage rate of composite membrane reduces with the temperature, the maximum IL wastage rate of 36% with the temperature is 20 °C is much lower than data reported by other researchers, indicating this type of composite membranes have better IL retention capacity. In addition, the proton conductivities of composite membrane are much higher than those of H3PO4 doped composite membrane and Nafion117 and the maximum proton conductivity(0.057 S/cm) was achieved by ABPBI/3SO-[BMIM]BF4-15.