208
7 Nanomaterials for Supercapacitors
7.3.4 Conductive Polymer
The conductive polymer with redox ability is another kind of important pseudocapacitor material, mainly including polyaniline (PANI), polypyrrole, and polythiophene. These conducting polymers primarily store energy through the process of
doping/dedoping of conjugated π bond in the bulk phase (redox process). During
oxidation (charge), ions enter into the structure of the polymer. During reduction
(discharge), the ions return to the electrolyte from the polymer’s structure. The
entire process (i.e., the doped and dedoped reactions of n-type or p-type elements
store charge) occurs not only on the surface, but also in the whole bulk phase of
the material. Thus the conductive polymer possesses a higher specific capacitance.
As the electrode material of supercapacitor, the conductive polymer has the characteristics of low cost and little impact on the environment. However, owing to the
reversible electrochemical doping and dedoping process, the conductive polymer
will undergo obvious volume swelling, resulting in reduced conductivity and structural damage. Therefore, its cyclic stability and rate performance are relatively poor.
The construction of conductive polymer-based nanocomposites can solve the above
problems.
Xu et al. (2010) constructed the nanocomposites of PANI and graphene and found
that the morphologies of PANI could be controlled by adjusting the concentrations
of aniline and graphene oxide (GO) owing to the different nucleation mechanism
(Fig. 7.6a). When the ratio of aniline monomer to GO was 0.05, the hierarchical
composite by combining 1D conducting PANI nanowires with 2D GO nanosheets
were successfully constructed. As shown in Fig. 7.6b, PANI nanowire arrays were
vertically aligned on GO substrate. The specific capacitance of the composite could
reach to 555 F g
−1 at 0.2 A g
−1 , which was much higher than 298 F g
−1 at the same
condition (Fig. 7.6c). Also, the cycle life of the nanocomposites was much better
than that of randomly connected PANI nanowires. The better performance is due to
the synergistic effect of GO and PANI.
Chen et al. (2016) synthesized porous perchlorate-doped polypyrrole electropolymerized on Ni nanotube arrays (NiNTAs@PPy). The NiNTAs were obtained by
utilizing pre-synthesized ZnO-nanorod arrays as the sacrificial template via a simple
electrodeposition method (Fig. 7.7a). As shown in Fig. 7.7b, c, NiNTAs@PPy
presented the parallel arrangement of uniformly hollow nanotubes. Perchloratedoped PPy was densely grown on both the outer and inner surfaces of the nanotubes.
As the electrode of supercapacitor, NiNTAs@PPy showed good cyclic performance
with 75.3% capacitance retention after 10,000 cycles (Fig. 7.7d).
7.3.5 MXene
MXene, as a new 2D layered material, has drawn researchers’ attention due to its
remarkable electrochemical properties. As electrode materials of SCs, MXene can
7 Nanomaterials for Supercapacitors
7.3.4 Conductive Polymer
The conductive polymer with redox ability is another kind of important pseudocapacitor material, mainly including polyaniline (PANI), polypyrrole, and polythiophene. These conducting polymers primarily store energy through the process of
doping/dedoping of conjugated π bond in the bulk phase (redox process). During
oxidation (charge), ions enter into the structure of the polymer. During reduction
(discharge), the ions return to the electrolyte from the polymer’s structure. The
entire process (i.e., the doped and dedoped reactions of n-type or p-type elements
store charge) occurs not only on the surface, but also in the whole bulk phase of
the material. Thus the conductive polymer possesses a higher specific capacitance.
As the electrode material of supercapacitor, the conductive polymer has the characteristics of low cost and little impact on the environment. However, owing to the
reversible electrochemical doping and dedoping process, the conductive polymer
will undergo obvious volume swelling, resulting in reduced conductivity and structural damage. Therefore, its cyclic stability and rate performance are relatively poor.
The construction of conductive polymer-based nanocomposites can solve the above
problems.
Xu et al. (2010) constructed the nanocomposites of PANI and graphene and found
that the morphologies of PANI could be controlled by adjusting the concentrations
of aniline and graphene oxide (GO) owing to the different nucleation mechanism
(Fig. 7.6a). When the ratio of aniline monomer to GO was 0.05, the hierarchical
composite by combining 1D conducting PANI nanowires with 2D GO nanosheets
were successfully constructed. As shown in Fig. 7.6b, PANI nanowire arrays were
vertically aligned on GO substrate. The specific capacitance of the composite could
reach to 555 F g
−1 at 0.2 A g
−1 , which was much higher than 298 F g
−1 at the same
condition (Fig. 7.6c). Also, the cycle life of the nanocomposites was much better
than that of randomly connected PANI nanowires. The better performance is due to
the synergistic effect of GO and PANI.
Chen et al. (2016) synthesized porous perchlorate-doped polypyrrole electropolymerized on Ni nanotube arrays (NiNTAs@PPy). The NiNTAs were obtained by
utilizing pre-synthesized ZnO-nanorod arrays as the sacrificial template via a simple
electrodeposition method (Fig. 7.7a). As shown in Fig. 7.7b, c, NiNTAs@PPy
presented the parallel arrangement of uniformly hollow nanotubes. Perchloratedoped PPy was densely grown on both the outer and inner surfaces of the nanotubes.
As the electrode of supercapacitor, NiNTAs@PPy showed good cyclic performance
with 75.3% capacitance retention after 10,000 cycles (Fig. 7.7d).
7.3.5 MXene
MXene, as a new 2D layered material, has drawn researchers’ attention due to its
remarkable electrochemical properties. As electrode materials of SCs, MXene can