86
5 Synthesis of Three-Dimensional Nanomaterials
2015). The as-prepared GN2.5% exhibits higher specific capacitance compared to
the individual carbon materials and better long-periodic stability after thousands
of cycles. Moreover, the conclusions are noteworthy: (1) GN2.5% shows excellent specific capacitance compared to that of MRF, due to the unique electron
conduction in graphene; the disorder and defect in graphene sheets are overcome by
removing oxygen-containing groups and restoring the conjugated structure; (2)
Because N-doped sites could serve as active sites to enhance the affinities with carrier
ions in the Faradaic reactions, the ample doped N would improve the pseudocapacitance, meanwhile the oxygen-containing groups could decrease the hydrophobicity
of carbon materials and charge transport resistance; (3) Compared to RG and GNs
with high GO content, the favorable morphology effect of GN2.5% is conducive to
charges stored in the charging process and adsorption capacity of carrier ions; (4)
The high capacitance is obtained from carbon material with larger surface area and
narrower pores. And the micropore plays the more significant role than mesopore
and specific surface in improving capacitance. In short, the approach proposed in this
work could open up a general route to prepare the laminated and N-doped electrode
material with highly promising application in energy storage.
Similarly, a rich N-doped porous carbon with large specific surface area as well as
enhanced specific capacitance for supercapacitors was synthesized from poly(acrylic
acid)/methylated melamine-formaldehyde resin through sol-gel process at ambient
temperature for 24 h, followed by calcination and carbonization at 350 °C and 500 °C,
respectively, for 1 h and KOH activation at 700 °C for 2 h under N 2 atmosphere (from
Jiang et al. 2015). The specific surface area of C-700-1.5 with a nitrogen content of
8.8 wt% is up to 2674 m
2 g
−1 .
What is more, due to the synergy effect, more and more researchers pay attention
to combing carbon material with metal oxide in order to achieve better nanomaterial.
Dam et al. reported a facile and simple approach to synthesize a composite of mesoporous NiO nanowires and graphene nanosheets applied in supercapacitor applications (Dam et al. 2014). A one-pot sol-gel method in a water/ethylene glycol mixture
in combination with a graphene oxide was used to prepare the Ni precursor. Heat
treatment in air was carried out to thermally reduce the graphene oxide to graphene
and to convert the Ni precursor to NiO. NiO nanowires showed a rough surface,
with a diameter of around 60 nm and are homogeneously deposited on the graphene
sheets. In comparison with its counterparts, the NiO/graphene nanocomposite shows
superior pseudocapacitive properties such as high specific capacitance, good cyclic
performance, and excellent discharge rate capability. As a result of the synergistic
effect of the addition of graphene as elastic conductive channels, the as-prepared
material demonstrates better charge transport and more favorable ionic diffusion. In
addition, a novel approach is introduced using sol-gel dip-coating method to fabricate ZnO/rGO/ZnO sandwich as flexible high-performance supercapacitor electrode
materials by Ghorbani et al. (2017). This ZnO/rGO/ZnO paper shows amazing flexibility based on freestanding GO paper as a new substrate for deposition of ZnO
thin films. Obtained ZnO thin film on GO paper leads to the dense layer with unaffected layered structure of GO paper. The sandwich papers show the most proper
morphology and performance as well as homogeneous ZnO thin film formation on
5 Synthesis of Three-Dimensional Nanomaterials
2015). The as-prepared GN2.5% exhibits higher specific capacitance compared to
the individual carbon materials and better long-periodic stability after thousands
of cycles. Moreover, the conclusions are noteworthy: (1) GN2.5% shows excellent specific capacitance compared to that of MRF, due to the unique electron
conduction in graphene; the disorder and defect in graphene sheets are overcome by
removing oxygen-containing groups and restoring the conjugated structure; (2)
Because N-doped sites could serve as active sites to enhance the affinities with carrier
ions in the Faradaic reactions, the ample doped N would improve the pseudocapacitance, meanwhile the oxygen-containing groups could decrease the hydrophobicity
of carbon materials and charge transport resistance; (3) Compared to RG and GNs
with high GO content, the favorable morphology effect of GN2.5% is conducive to
charges stored in the charging process and adsorption capacity of carrier ions; (4)
The high capacitance is obtained from carbon material with larger surface area and
narrower pores. And the micropore plays the more significant role than mesopore
and specific surface in improving capacitance. In short, the approach proposed in this
work could open up a general route to prepare the laminated and N-doped electrode
material with highly promising application in energy storage.
Similarly, a rich N-doped porous carbon with large specific surface area as well as
enhanced specific capacitance for supercapacitors was synthesized from poly(acrylic
acid)/methylated melamine-formaldehyde resin through sol-gel process at ambient
temperature for 24 h, followed by calcination and carbonization at 350 °C and 500 °C,
respectively, for 1 h and KOH activation at 700 °C for 2 h under N 2 atmosphere (from
Jiang et al. 2015). The specific surface area of C-700-1.5 with a nitrogen content of
8.8 wt% is up to 2674 m
2 g
−1 .
What is more, due to the synergy effect, more and more researchers pay attention
to combing carbon material with metal oxide in order to achieve better nanomaterial.
Dam et al. reported a facile and simple approach to synthesize a composite of mesoporous NiO nanowires and graphene nanosheets applied in supercapacitor applications (Dam et al. 2014). A one-pot sol-gel method in a water/ethylene glycol mixture
in combination with a graphene oxide was used to prepare the Ni precursor. Heat
treatment in air was carried out to thermally reduce the graphene oxide to graphene
and to convert the Ni precursor to NiO. NiO nanowires showed a rough surface,
with a diameter of around 60 nm and are homogeneously deposited on the graphene
sheets. In comparison with its counterparts, the NiO/graphene nanocomposite shows
superior pseudocapacitive properties such as high specific capacitance, good cyclic
performance, and excellent discharge rate capability. As a result of the synergistic
effect of the addition of graphene as elastic conductive channels, the as-prepared
material demonstrates better charge transport and more favorable ionic diffusion. In
addition, a novel approach is introduced using sol-gel dip-coating method to fabricate ZnO/rGO/ZnO sandwich as flexible high-performance supercapacitor electrode
materials by Ghorbani et al. (2017). This ZnO/rGO/ZnO paper shows amazing flexibility based on freestanding GO paper as a new substrate for deposition of ZnO
thin films. Obtained ZnO thin film on GO paper leads to the dense layer with unaffected layered structure of GO paper. The sandwich papers show the most proper
morphology and performance as well as homogeneous ZnO thin film formation on