Among thermoplastics polymers, polybenzimidazole (PBI), short for poly [2, 2’-(m-phenylene)-5,5’-
bisbenzimidazole], is known for its exceptional thermal and chemical stability at elevated
temperature. It is usually employed to fabricate high-performance protective tools such as synthetic
fibers for firefighter’s gear, astronaut and welder’s suits, as well as in aircraft walls, as for examples.
However, the most recent application of PBI polymer is as membrane in high-temperature polymer
electrolyte membrane fuel cell (HT-PEMFC). PBI membranes must be doped with inorganic acids, like
phosphoric acid (PA), to substantially improve their conductivity properties. Nevertheless, when
doped, its mechanical integrity gets much worse, representing one of their major handicaps for the
application of doped PBI in PEMFC devices.
The addition of inorganic materials, such as titanium dioxide, silica or clay, into proton exchange
membranes (PEM) is known to substantially improve their mechanical and thermal properties, as
reported in previous studies; and, hence the capability of the membrane for high temperature fuel
cell applications. In the present study, PBI membranes were prepared by solvent casting after the
incorporation of chemically modified polyethyleneimine-silica nanoparticles (Si-PEI NPs). The use of
PEI (Mw ≈ 800 g/mol) as silica coupling agent is intended to improve the interfacial interactions
between the organic-inorganic surrounding in the polymer matrix.
A detailed description of the synthesis and the methods used for the characterization of the new
membranes is reported. Results demonstrated that chemically modified PBI-Si-PEI membranes have
better properties than the pristine PBI films. Moreover, the conductive properties were also
enhanced after the doping process with the PA molecules.
Additionally, to the study above mentioned, another dopant molecule composed by
dodecylbenzenesulfonic acid (DBSA) was investigated. It consisted in a brief study where the
conductive properties were also approached. The DBSA molecules perform as dopant and plasticizer,
due to the high number of methylene groups inside its chemical structure.
