Page 296 - Polymer-based Nanocomposites for Energy and Environmental Applications

Polymer nanocomposite materials in energy storage: Properties and applications 265

In the past two decades, transition metal oxides and electrically conducting poly-
mers are considered as the most promising pseudocapacitor materials for the super-
capacitors. Transition metal oxides are attractive electrode material for the
supercapacitors because of their excellent charge storage characteristics and thermal,
chemical, and mechanical stability. Several transition metal oxides such as NiO [211],
CoO [212], CuO [213], MnO 2 [214–217],WO 3 [218],VO x [219], and RuO 2 [220]
have been successfully explored as pseudocapacitor material. Recently, ternary cobalt
oxide’manganese dioxide’nickel oxide 1D nanotubes have been used as electrode
material for supercapacitor with high performance [221]. Manganese dioxide is the
most widely explored pseudocapacitor material among all the transition metal oxides
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because of their high theoretical capacitance (1370 F g ), widespread occurrence,
good cyclic stability, and environment-friendly nature [214,222–224]. However, its
low electric conductivity is a major barrier toward its commercialization, which in
turn leads to low capacitance and low output power, at high current density
[121,217]. Moreover, it tends to be highly unstable even in the slightly acidic envi-
ronment of the supercapacitor [216,225]. Performance of manganese dioxide as pseu-
docapacitor material depends on the morphology, particle size distribution, and
specific surface area; therefore, various nanostructure forms of MnO 2 have been
explored [215,216,225,226]. Nanocomposite of conducting polymers with MnO 2
can combine the good electric conductivity of the polymer and cyclic stability of
MnO 2 by synergic interaction. Such hybrid material has shown high capacitance
and high cyclic stability [227–229].
Sun et al. synthesized PANI-coated honeycomb-like MnO 2 nanosphere to take
advantage of both PANI and MnO 2 by synergic interaction, by two-step synthesis pro-
cedure. The synthesis procedure is elucidated in Fig. 9.9A. FESEM image showed that
the MnO 2 nanosphere of size 90 nm is fully covered with polyaniline. Electrochemical
tests demonstrate that capacitive performance of the binary composite is strongly
dependent upon the mass ratio of MnO 2 and aniline. When the ratio is 1:1, the electrode
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shows a high specific capacitance of 565 F g 1 (specific capacity of 126 mAh g )at a
discharge current density of 0.8 A g 1 and a high specific capacity of 143 mAh g 1 at
the scan rate of 20 mV s 1 in 0.5 M Na 2 SO 4 –0.5 M H 2 SO 4 solution. The
nanocomposite could retain 77% of the original capacitance even after 1000 cycles
at 8 A g 1 discharge rate (Fig. 9.9). Similarly, PTh/MnO 2 [122,230] and PPy/MnO 2
[231] have shown better performance than individual polymer and MnO 2 .
In order to further enhance the performance of the electrode material, many
researchers have attempted to synthesize and test ternary composite materials having
electric conducting polymer as one component. Recently, in order to develop flex-
ible and wearable supercapacitor, Yun et al. coated a nanothickness layer of poly-
pyrrole over the MnO 2 nanoparticles, which were grown on CNT textile to make
a ternary with MnO 2 pseudocapacitor. The composite was fabricated using proce-
dure as shown in Fig. 9.10A. The electrochemical characterization results show
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high initial capacitance of 461 F g , which is 38% higher than MnO 2 /CNT
for the composite. The composite showed excellent cyclic stability of 93.3%
after 10,000 cycles. It also showed remarkable tensile strength that is important
for flexible pseudocapacitor [232].