198
7 Nanomaterials for Supercapacitors
of desolvation and the improvement of the storage charge of unit specific capacitance,
the area specific capacitance increased sharply with the decrease of the pore size.
For typical activated carbon materials, the Brunauer-Emmett-Teller (BET)
specific surface area is generally from 1000 to 2000 m
2 g
−1 . The gravimetric capacitance of the materials is usually 100–120 F g
−1 in organic electrolytes. For further
improving the performance of activated carbon materials, Ruoff et al. (Zhu et al.
2011) synthesized a new active carbon (donated as activated graphene) via a chemical activation with KOH for microwave exfoliated graphite oxide (MEGO), which
possesses a specific surface area of up to 3100 m
2 g
−1 . When measured in an organic
(BMIM BF 4 ) electrolyte, the capacitance of activated graphene was 200 F g
−1 at
0.7 A g
−1 . This material also shows stable cycling performance, 97% of its initial
capacitance was retained at 2.5 A g
−1 after 10,000 cycles.
7.2.2 Ordered Mesoporous Carbon Materials
Ordered mesoporous carbon materials not only possess high specific surface area,
but also have large pore size and orderly pore arrangement, which is conducive to the
diffusion of electrolyte. Therefore, it becomes a good electrode material for EDLCs.
For instance, CMK-3 mesoporous carbon was prepared by the hard template method,
exhibiting a fiber-like close stacking framework with a specific BET surface area of
900 m
2 g
−1 and a pore diameter of 3.90 nm (Li et al. 2007). When utilized as the
electrode material in organic electrolytes, CMK-3 showed a specific capacitance of
90 F g
−1 at 50 mV s
−1 . Dai et al. (Wang et al. 2010) effectively enhanced the specific
surface area from 520 to 1940 m
2 g
−1 via the KOH activation for the mesoporous
carbon. The specific capacitance was increased from 71 to 188 F g
−1 .
To further enhance the specific capacitance of mesoporous carbons, the introduction of surface functional groups is a promising way. The functional groups could
proceed a reversible redox reaction, thus providing pseudocapacitance. Recently,
Huang et al. (Lin et al. 2015) reported a breakthrough work about the mesoporous
carbon with functional groups as the electrode materials of supercapacitor. N-doped
ordered mesoporous few-layer-graphene carbon (OMFLC-N) was prepared via the
combination of chemical vapor deposition (CVD) method and sacrificial template
method (Fig. 7.1a). As shown in Fig. 7.1b, c, OMFLC-N showed ordered mesopores and few-layer-graphene like structure. When used as the electrode material,
it exhibited nearly rectangular CV curves and symmetric features (Fig. 7.1d). The
optimal OMFLC-N electrode achieved an ultrahigh specific capacitance of 790 F g
−1
in 0.5 M H 2 SO 4 electrolyte at 1 A g
−1 , the corresponding value was 720 F g
−1 in
2 M Li 2 SO 4 electrolyte (Fig. 7.1e). The improvement mostly stemmed from the
pseudocapacitance through robust redox reactions at the defects of nitrogen atoms.
The inert graphene-like layered carbon was transformed into a material with electrochemical activity while maintaining good electric conductivity. This result provides
an excellent low-cost carbon-based material for supercapacitors.
7 Nanomaterials for Supercapacitors
of desolvation and the improvement of the storage charge of unit specific capacitance,
the area specific capacitance increased sharply with the decrease of the pore size.
For typical activated carbon materials, the Brunauer-Emmett-Teller (BET)
specific surface area is generally from 1000 to 2000 m
2 g
−1 . The gravimetric capacitance of the materials is usually 100–120 F g
−1 in organic electrolytes. For further
improving the performance of activated carbon materials, Ruoff et al. (Zhu et al.
2011) synthesized a new active carbon (donated as activated graphene) via a chemical activation with KOH for microwave exfoliated graphite oxide (MEGO), which
possesses a specific surface area of up to 3100 m
2 g
−1 . When measured in an organic
(BMIM BF 4 ) electrolyte, the capacitance of activated graphene was 200 F g
−1 at
0.7 A g
−1 . This material also shows stable cycling performance, 97% of its initial
capacitance was retained at 2.5 A g
−1 after 10,000 cycles.
7.2.2 Ordered Mesoporous Carbon Materials
Ordered mesoporous carbon materials not only possess high specific surface area,
but also have large pore size and orderly pore arrangement, which is conducive to the
diffusion of electrolyte. Therefore, it becomes a good electrode material for EDLCs.
For instance, CMK-3 mesoporous carbon was prepared by the hard template method,
exhibiting a fiber-like close stacking framework with a specific BET surface area of
900 m
2 g
−1 and a pore diameter of 3.90 nm (Li et al. 2007). When utilized as the
electrode material in organic electrolytes, CMK-3 showed a specific capacitance of
90 F g
−1 at 50 mV s
−1 . Dai et al. (Wang et al. 2010) effectively enhanced the specific
surface area from 520 to 1940 m
2 g
−1 via the KOH activation for the mesoporous
carbon. The specific capacitance was increased from 71 to 188 F g
−1 .
To further enhance the specific capacitance of mesoporous carbons, the introduction of surface functional groups is a promising way. The functional groups could
proceed a reversible redox reaction, thus providing pseudocapacitance. Recently,
Huang et al. (Lin et al. 2015) reported a breakthrough work about the mesoporous
carbon with functional groups as the electrode materials of supercapacitor. N-doped
ordered mesoporous few-layer-graphene carbon (OMFLC-N) was prepared via the
combination of chemical vapor deposition (CVD) method and sacrificial template
method (Fig. 7.1a). As shown in Fig. 7.1b, c, OMFLC-N showed ordered mesopores and few-layer-graphene like structure. When used as the electrode material,
it exhibited nearly rectangular CV curves and symmetric features (Fig. 7.1d). The
optimal OMFLC-N electrode achieved an ultrahigh specific capacitance of 790 F g
−1
in 0.5 M H 2 SO 4 electrolyte at 1 A g
−1 , the corresponding value was 720 F g
−1 in
2 M Li 2 SO 4 electrolyte (Fig. 7.1e). The improvement mostly stemmed from the
pseudocapacitance through robust redox reactions at the defects of nitrogen atoms.
The inert graphene-like layered carbon was transformed into a material with electrochemical activity while maintaining good electric conductivity. This result provides
an excellent low-cost carbon-based material for supercapacitors.