Page 217 - Polymer-based Nanocomposites for Energy and Environmental Applications

Polymer-based nanocomposites for energy and environmental applications 189

(the Debye length). A linear connection between specific capacitance (C) and specific
surface area (A) based on Eq. (6.2) [62]. It is believed that the EDLC must have
superior capacitance related to conventional capacitors due to smaller separation dis-
tance [63,64]. Moreover, considerably larger area of electrode/electrolyte interface
can advance the capacitance of EDLC. Additionally, exceptional electrical conduc-
tivity and good wettability of electrolyte can further improve the capacitance in
EDLCs [65].
To improve the capacitance, electrochemical redox materials can be combined
with the conductive activated carbon to make electrode materials for supercapacitors.
The energy storage mechanism at the interface between electrode and electrolyte is
not through a physical method, few rapid reversible redox reactions taken place to
attain higher capacitance compared with that of pure carbon-based EDLCs [66]. These
types of electrochemical capacitors are called pseudocapacitors. One of the commonly
used electrode materials for pseudocapacitors is ruthenium oxide [67]. Pseudo-
capacitors store energy in three different processes: (i) surface adsorption of ions from
the electrolyte, (ii) redox reactions comprising ions from the electrolyte solution, and
(iii) doping/undoping of active CP materials.
Another type of supercapacitors that store energy with dissimilar electrodes is
asymmetrical supercapacitors. The electrodes are composed of a battery-like
faradic electrode and a capacitive carbon-based electrode. This distinctive system
provides the advantage of adjusting operating voltage window and improves the
energy density credited to the electrochemical redox behaviors at the faradic elec-
trode [68]. The prototype of asymmetrical supercapacitors was further researched
by many groups [69–71].

6.2.2 Polypyrrole (PPys) NCs

Nowadays, electronically CP such as PPys, PANIs, and PTs and their derivatives are
used for enhancement of electronic conductivity properties. These conducting poly-
mers find the various applications such as energy storage devices, solar cells, and sen-
sors. These conducting polymers are produced from their monomers by numerous
synthesis processes. For instance, electrochemically fabricated electronic conduc-
ting polymers undergo via electrochemical polymerization pathway [72,73]. PPys
NCs have been broadly inspected as electrode materials for lithium-ion batteries
[74–76]. Highly conductive PPys NCs can promote the electronic conductivity of
the electrode materials and contribute to the capacity of the electrode during cycling.
Moreover, PPys NCs play a role as a binder to improve the interaction between the
particles [77]. PPys NCs exist in dissimilar conducting grades, are dispersible in water,
and have the ability to coat as thin film via spin or dip coating or electropolymerization
process [78].
PPys NCs with laponite conducting polymer are conducting in the doped and oxi-
dative state schematically shown in Fig. 6.3. The electrochemical activities of PPy
NCs have been widely investigated in various types of electrolytes, and it has been
displayed that faradaic processes consisting of a reversible redox reaction govern
the electronic behaviors with a specific capacity of up to 400 F/g [79].