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electrolytes based on an amorphous polymer poly[(oxyethylene)
8
methacrylate],
POM and lithium montmorillonite clay have also been tested as 'salt-free' elec-
trolytes in lithium polymer batteries [
148
]. In a recent review appeared from Keith
Scott's research team, it has consolidated the various research aspects and activities
related to the development of solid acids as an electrolyte material for PEM water
electrolysers [
149
].
Hydroxide-conducting polymer membranes—also termed as anion-exchange
membranes (AEMs)—are another interesting variety of ion-conducting PEMs that
recently started gaining more interest towards alkaline fuel cells and electrolyser.
Several types of polymers, such as poly(2,6-dimethyl-1,4-phenylene oxide) (PPO),
copolymer of chloromethylstyrene and divinylbenzene, PVDF-vinyl-benzyl chlo-
ride, and poly(vinyl alcohol) (PVA) poly(1,3-diethyl-1, 1-vinyl imidazolium bro-
mide) 1,4-diazabicyclo-[2.2.2]-octane polysulphone, quaternary ammonium grafted
poly vinyl benzyl chloride, have been used for the preparation of AEMs [
150
-
154
].
The preparation procedure for AEMs based on PVA and copolymer of poly(acry-
lonitrile (PAN)-dimethylamio ethylmethacrylate) (DMAEMA) with strongly basic
quaternary ammonium in aqueous media has also been reported [
155
]. These
studies reveal that different ion-conducting PEMs including proton are being
developed for future energy needs and a breakthrough in any of these materials
might open up the electrochemical power systems with improved efficiency.
13 Progress in Bipolar Plate Developments
The current graphite-based state-of-art bipolar plates in PEMFCs face severe
concerns mainly due to their higher weight, fragility, brittleness and volume.
Despite their inherent qualities, like desirable electrical conductivity, appreciable
thermal and chemical properties but due to their inadequate mechanical properties
are restricts their usage in PEMFC stacks. Such drawback necessitates the search
for alternative options such as metallic alloys and conducting polymer-based
composites. Conducting polymer-based composites provide a promising option,
but needs higher level of carbon filler ([50 vol%) to achieve the required elec-
trical and thermal conductivity. This also results in several manufacturing and
processing related issues. However, CNTs offer significant advantages due to their
high electrical properties and ability to form composites with conduction polymer
[
156
-
159
]. For example, carbon nanotube composite with polyethylene terepht-
halte (PET)/polyvinylidene fluoride (PVDF) blend result in continuous conductive
path provided by the CNTs while the PVDF phase offers crack bridging and PET/
PVDF interface provides crack deflection for the composite. Due to this combi-
nation, the CNT-PET/PVDF composite has better electrical conductivity, strength
and elongation and is considered as one of the promising materials for bipolar
plate applications [
159
]. Recently, graphite-phenol formaldehyde resin show
improved bend strength that is necessary for bipolar plate applications. Similarly,
CNT-reinforced vinyl ester nanocomposite is shown to have bulk (in-plane)
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