Page 290 - Polymer-based Nanocomposites for Energy and Environmental Applications

260 Polymer-based Nanocomposites for Energy and Environmental Applications

from aniline monomer, simple doping/dedoping mechanism, excellent electric con-
ducting, and environmental stability [26]. Polyaniline itself can be used as electrode
material for supercapacitor. Sivakkumar et al. synthesized PANI nanofiber using
interfacial polymerization using aniline. When used as electrode in an aqueous super-
capacitor, PANI nanofiber showed high initial capacitance of 554 F g 1 at 1 A g 1
discharge rate. However, with very low cyclic stability, after 1000 cycles, the specific
capacitance was only 75 F g 1 [196]. Huang et al. synthesized a binder-free 3D struc-
ture by a thin-film (<11 nm) deposition over aligned CNT array grown on Al-foil.
It is important to control the thickness of the PANI film to utilize the high capacitance
of PANI, active sites for ionic conductivity increase, and electric conductivity
and enhance the synergic interaction between PANI and CNT. PANI@AACNT
1
showed high specific energy of 18.9 Wh kg , high maximum specific power of
1
11.3 kW kg 1 of the active material in an aqueous electrolyte at 1.0 A g , and excel-
1
lent rate performance and cycling stability. A high specific energy of 72.4 Wh kg ,a
1
high maximum specific power of 24.9 kW kg , and a good cycling performance of
the active material are obtained in an organic electrolyte [197]. Recently, Imani et al.
studied the effect of adding a thin layer of PANI over MWCNTs. The tubular structure
morphology showed good initial capacitance of 439.17 F g 1 at the current density of
10mA cm 2 [198]. Polypyrrole is another conducting polymer that has been used
extensively as an electrode for supercapacitor. Jurewicz et al. prepared PPy/CNT
nanocomposite by electrochemical polymerization of pyrrole as 5 nm thin film of
1
PPy on the CNT. The composite showed initial specific capacitance 163 F g ,
1
whereas pristine CNT showed only 50 F g . The open network of CNT-polypyrrole
favors the formation of 3D double layer [199]. Shi et al. reported high-capacitance
PPy/CNT electrode [200] (Fig. 9.6).
2
Graphene is a sp -hybridized carbon-based material with a hexagonal (benzene
ring) monolayer network. Graphene is an allotrope of carbon, which is a strictly
2D material with exceptionally high specific surface area (theoretical value of
2 1
2630 m g ) [201] and high electric conductivity [202], low-cost large-scale produc-
tion, excellent mechanical stability, and good chemical and thermal stability
[31,32,203,204]. Theoretically, supercapacitors of graphene and its derivatives can
1
achieve an initial capacitance of 550 F g , which corresponds to a theoretical specific
2 1
2
capacitance of 21 μFcm . But a large portion of the area (2630 m g ) of graphene
remains inaccessible due to restacking of the individual sheets owing the π-π interac-
tion and van der Waals forces [177]. As a result, in practice, the specific capacitance of
graphene-based materials is between 10 and 135 F g 1 due to the agglomeration of the
graphene sheets [31,32,203,204]. Making polymer nanocomposite with conducting
polymer is an excellent way to improve the performance of graphene-based materials.
In one such attempt, graphene/polyaniline nanocomposite was synthesized by in situ
anodic electrochemical polymerization of aniline on graphene paper. Specific capac-
itance of 233 F g 1 was achieved with most of the capacitance came from the pseu-
docapacitance from the polyaniline film. The EDLC from the graphene was very low
due to the agglomeration of the graphene sheetlike structure [205]. Zhang et al.
aimed to synthesize a homogenous polymer nanocomposite of PANI and graphene.
They first mixed aniline with GNS and then oxidized by the in situ polymerization.