Polymer electrolyte membrane fuel cells (PEMFCs) are one of the most promising
clean technologies under development. However, the main obstacles for
commercialising PEMFCs are largely attributed to the technical limitations and cost
of current PEM materials such as Nafion. Novel poly(2,5-benzimidazole)
(ABPBI)/POSS based polymer composite electrolyte membranes with excellent
mechanical and conductivity properties were developed in this project including (I)
ABPBI, polybenzimidazole (PBI) and their copolymers were synthesised by solution
polymerisation and their chemical structures were confirmed by FTIR and elemental
analysis. ABPBI/ActaAmmonium POSS (ABPBI/AM) and ABPBI/TriSilanolPhenyl
POSS (ABPBI/SO) composites were also synthesised in situ. High quality polymer
and composite membranes were fabricated by a direct cast method; and (II) The
mechanical and thermal properties, microstructure and morphology, water and
H3PO4 absorbility and proton conductivity of phosphoric acid doped and undoped
ABPBI and ABPBI/POSS composite membranes were investigated. SEM/TEM
micrographs showed that a uniform dispersion of POSS nano particles in ABPBI
polymer matrix was achieved. The best performances on both mechanical properties
and proton conductivities were obtained from the ABPBI/AM composite membrane
with 3 wt% of POSS (ABPBI/3AM). It was found that both the water and H3PO4
uptakes were increased significantly with the addition of POSS due to formation of
hydrogen bonds between the POSS and H2O/H3PO4, which played a critical role in
the improvement of the conductivity of the composite membranes at temperatures
over 100oC. ABPBI/3AM membranes with H3PO4 uptake above 117% showed best
proton conductivities at both hydrous and anhydrous conditions from room
temperature to 160oC, which is comparable with the conductivity of commercial
Nafion 117 at 20oC in water-saturated condition, indicating that these composite
membranes could be excellent candidates as a polymer electrolyte membrane for
high temperature applications. A new mechanism for illustrating the improved proton
conductivity of composite membranes was also developed