206
7 Nanomaterials for Supercapacitors
1 mV s
−1 . Cao et al. (2014) fabricated hierarchical porous NiO nanotube arrays on
the Ni foam substrate by electrodeposition method. The specific capacitance of the
obtained NiO nanotube arrays was 675 F g
−1 at 2 A g
−1 . Similarly, inspired by the
larger surface area and better conductivity brought by 3D network of nickel foam,
Cheng et al. (2015) prepared ultrathin mesoporous NiO nanosheets in situ on the Ni
foam. Due to the enhanced conductivity and ion transfer of the hybrid structure, the asprepared additive/binder-free electrodes achieved an excellent specific capacitance
of 2504.3 F g
−1 and remarkable cycling stability with no obvious degradation even
after 45,000 cycles.
Lin et al. (2018) designed and synthesized a novel core-shell structure of
graphene@NiO (G@NiO) nanosheet arrays as electrodes for high-performance
supercapacitors. As the illustration shows (Fig. 7.5a), NiO nanosheet arrays were
anchored on g-Ni foam after the hydrothermal process, and then were changed into
vertically nanosized NiO particles wrapped in graphene layers via a plasma enhanced
chemical vapor deposition (PECVD) method. Among various samples with different
PECVD time, the G@NiO-1 (1 min) nanosheets showed more flexible outer surface
(Fig. 7.5b). Benefiting from the 3D conductive graphene frame-works and nanosized NiO, the optimized G@NiO hybrid electrodes delivered a remarkable specific
capacity of 1073 C g
−1 and excellent cycling performance with ≈99% retention after
10,000 cycles (Fig. 7.5c, d). Another NiO nanoparticles encapsulated in carbon and
SWCNTs composite was prepared by Majeed et al. via a floating catalyst chemical vapor deposition method (Majeed et al. 2017). The obtained binder-free electrode of carbon-encapsulated NiO nanoparticle decorated SWCNT films showed a
high specific capacitance of 1422 F g
−1 at 3 A g
−1 and good cycling stability with
92% of initial specific capacitance after 5000 cycles. By using nickel acetylacetone
and polyacrylonitrile as precursors, Li et al. fabricated NiO nanoparticles dispersed
in N-doped porous carbon nanofibers (NiO/PCNF) via an electrospinning method
followed by controlled heat treatment (carbonization at 800 °C) (Fig. 7.5e) (Li et al.
2018). The numerous multiscale nanopores can be obviously observed in Fig. 7.5f,
g, which is beneficial for the diffusion distance of ion/charge and contact between
electrolyte. Therefore, the NiO/PCNF-0.75 film electrode with superior surface area
achieved the best specific capacitance of 850 F g
−1 at 1 A g
−1 and a high specific
capacitance of 748 F g
−1 when the current density was up to 10 A g
−1 . Meanwhile, its specific capacitance was retained 96.7% of the initial capacitance even
after 10,000 cycles (Fig. 7.5h–j). A hierarchical NiO/carbon hollow sphere composite
(NiO/C-HS) was synthesized by Liu et al. through a semi-sacrificial template-assisted
hydrothermal process and the following calcination treatment (Liu et al. 2018a, b).
The prepared NiO/C-HS with carbon hollow spheres supporting well-dispersed NiO
nanosheets delivered a high specific capacitance of 686 F g
−1 at 1 A g
−1 and good
cycling stability of no obvious capacitance loss after 5000 cycles.
7 Nanomaterials for Supercapacitors
1 mV s
−1 . Cao et al. (2014) fabricated hierarchical porous NiO nanotube arrays on
the Ni foam substrate by electrodeposition method. The specific capacitance of the
obtained NiO nanotube arrays was 675 F g
−1 at 2 A g
−1 . Similarly, inspired by the
larger surface area and better conductivity brought by 3D network of nickel foam,
Cheng et al. (2015) prepared ultrathin mesoporous NiO nanosheets in situ on the Ni
foam. Due to the enhanced conductivity and ion transfer of the hybrid structure, the asprepared additive/binder-free electrodes achieved an excellent specific capacitance
of 2504.3 F g
−1 and remarkable cycling stability with no obvious degradation even
after 45,000 cycles.
Lin et al. (2018) designed and synthesized a novel core-shell structure of
graphene@NiO (G@NiO) nanosheet arrays as electrodes for high-performance
supercapacitors. As the illustration shows (Fig. 7.5a), NiO nanosheet arrays were
anchored on g-Ni foam after the hydrothermal process, and then were changed into
vertically nanosized NiO particles wrapped in graphene layers via a plasma enhanced
chemical vapor deposition (PECVD) method. Among various samples with different
PECVD time, the G@NiO-1 (1 min) nanosheets showed more flexible outer surface
(Fig. 7.5b). Benefiting from the 3D conductive graphene frame-works and nanosized NiO, the optimized G@NiO hybrid electrodes delivered a remarkable specific
capacity of 1073 C g
−1 and excellent cycling performance with ≈99% retention after
10,000 cycles (Fig. 7.5c, d). Another NiO nanoparticles encapsulated in carbon and
SWCNTs composite was prepared by Majeed et al. via a floating catalyst chemical vapor deposition method (Majeed et al. 2017). The obtained binder-free electrode of carbon-encapsulated NiO nanoparticle decorated SWCNT films showed a
high specific capacitance of 1422 F g
−1 at 3 A g
−1 and good cycling stability with
92% of initial specific capacitance after 5000 cycles. By using nickel acetylacetone
and polyacrylonitrile as precursors, Li et al. fabricated NiO nanoparticles dispersed
in N-doped porous carbon nanofibers (NiO/PCNF) via an electrospinning method
followed by controlled heat treatment (carbonization at 800 °C) (Fig. 7.5e) (Li et al.
2018). The numerous multiscale nanopores can be obviously observed in Fig. 7.5f,
g, which is beneficial for the diffusion distance of ion/charge and contact between
electrolyte. Therefore, the NiO/PCNF-0.75 film electrode with superior surface area
achieved the best specific capacitance of 850 F g
−1 at 1 A g
−1 and a high specific
capacitance of 748 F g
−1 when the current density was up to 10 A g
−1 . Meanwhile, its specific capacitance was retained 96.7% of the initial capacitance even
after 10,000 cycles (Fig. 7.5h–j). A hierarchical NiO/carbon hollow sphere composite
(NiO/C-HS) was synthesized by Liu et al. through a semi-sacrificial template-assisted
hydrothermal process and the following calcination treatment (Liu et al. 2018a, b).
The prepared NiO/C-HS with carbon hollow spheres supporting well-dispersed NiO
nanosheets delivered a high specific capacitance of 686 F g
−1 at 1 A g
−1 and good
cycling stability of no obvious capacitance loss after 5000 cycles.