Page 250 - Polymer-based Nanocomposites for Energy and Environmental Applications

222 Polymer-based Nanocomposites for Energy and Environmental Applications

molecules in organic dopant such as camphor sulfonic acid (CSA) and dodecylbenzene
sulfonic acid (DBSA) are replaced by a small size dopant (HCl) through the molecular
sieving phenomenon (doping, undoping, and redoping processes) [26].
Among the various morphologies of PANI, nanofibers show promising results in
hydrogen storage applications [27–30]. In standard condition, the reversible hydrogen
storage behavior in PANI nanofibers was first reported by Niemann et al. Here,
pressure-composition isotherm figures of these PANI nanofibers show that the rate
of hydrogen sorption was fast and extended plateau pressure of about 30 bar
(3 MPa) was achieved with a reversible cycling capacity of 3–4 wt% [27]. Unique
nanofibrous morphology and the surface properties are the reason to attain the above
results [27]. In another work, PANI nanofibers were prepared by oxidative polymeri-
zationusingorganicadditivelikesucrose,C 12 H 22 O 11 ,orsucralose,C 12 H 19 C l3 O 8 ,inthe
presence of aniline monomer. These prepared PANI fibers were soluble in water and
also in other polar organic solvents such as methanol, ethanol, DMF, and DMSO. It
is confirmed that these nanofibers show high-hydrogen absorption capability as
4.3 wt% at 298 K and 20 atm. This is because of the formation of nanopores during
the growth of nanofibers. Further, influence of sucrose on the hydrogen storage prop-
erties was reported [28]. Srinivasan et al. have prepared PANI fibers by traditional
chemicalsynthesismethods andfollowed byelectrospuntoobtainfibrous morphology.
The morphology of electrospun PANI fibers was shown in Fig. 8.3. The obtained PANI
fibers were tested through pressure-composition-temperature (PCT) measurements; it
reveals a reversible hydrogen storage capacity of 3–10 wt% at dissimilar temperatures
(Fig. 8.4). Endurance test of these PANI materials is studied by performing 66 cycles,
and the hydrogen kinetic sorption measurements show >6–10 wt%. SEM microstruc-
tural observations in Fig. 8.3 confirm the effective hydrogen uptake and releases. It is
clear that the density and the length of PANI fibers remain the same irrespective of the
synthesis conditions. It is seen that there are fibrillar swelling, breaking of fiber length,
and precipitations that are evidenced from SEM images of the hydrogenated and
dehydrogenated samples.These PANI fibers exhibit high-volumetric hydrogen storage
capacities of 3–10 wt%. This value is obtained as a result of the morphological swelling
credited to hydrogen interaction onthe surface and in bulkas analogous toconventional
metalhydrides.Moreover,achangeinthemicrostructure(nanofibrillarswellingeffect)
is noticed before and after hydrogen sorption [29].
A network morphology like PANI-polypyrrole composite materials was synthe-
sized via facile method. Here, PANI nanofibers (PANI-NF) were protected by a thin
layer of polypyrrole (PPY) that was prepared via vapor-phase polymerization [30].At
room temperature, hydrogen storage capacity of 0.46 wt% for HCl-doped PANI and
0.91 wt% for PANI-polypyrrole (PANI-PPY) composites was obtained. This twofold
increase in the composite materials is achieved due to the synergy of the PPY layer
that significantly fashioned more sorption sites for hydrogen storage. Notably, the size
of the dopant counteranions plays a major part in the hydrogen absorb process system,
and this resembles in a hydrogen uptake capacity of dissimilar composites of PANI-
NF dopants with various counteranion sizes. Among them, the loaded palladium
nanoparticles between PANI-NF and the PPY layer display a superior hydrogen
uptake capacity than the parent one [30].