A unique zirconium-based microporous MOF-808 constructed
from Zr6 nodes (Zr6O4(OH)4) and BTC
(benzene-1,3,5-tricarboxylic acid) synthesized herein has been further
tailored by radical in situ polymerization of 1-vinylimidazole alongside N,N′-methylene-bis(acrylamide) as
the cross-linker after their adsorption inside MOF pore channels.
The cross-linked architectures were incorporated as fillers at 2 and
4 wt % in sulfonated poly (ether ether ketone) (SPEEK) solution to
formulate mixed-matrix composite Proton Exchange Membranes (PEMs).
The composite membranes displayed considerably higher proton conductivity,
improved fuel cell performance, and thermal stability than pristine
SPEEK. The highly ordered crystal-controlled 3D polymeric cross-linked
networks created in the MOF channels address the undesirable leaching
associated with adding low-molecular-weight azoles in membranes. Additionally,
it generates highly ordered long-range proton-conducting channels
through the MOF pores. The acid–base interaction between the
imidazole and sulfonic functional groups causes the conductivity of
protons to increase to 0.05 S/cm at 80 °C and 70% RH for the
S4P3M membrane containing 4 wt % complex filler, which is 16.6-fold
higher than that of pure SPEEK. The membrane retains a proton conductivity
of up to 0.04 S/cm at 100 °C and 40% RH, indicating its proton-conducting
abilities at low humidity conditions. Furthermore, S4P3M achieves
a peak power density of 310 mW/cm2 at 60 °C and 347
mW/cm2 at 80 °C under 70% relative humidity, which
are higher than those in several other reported literature studies
on SPEEK-based membranes.
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