84
5 Synthesis of Three-Dimensional Nanomaterials
(CA), oxalic acid (OA) as well as ethylenediamine tetraacetic acid (EDTA) explored
during the fabrication and the tested electrochemical and supercapacitor properties
(Zhu et al. reported) (Zhu et al. 2014) (1) Ni(Ac) 2 · 4H 2 O (0.05 M) and Co(Ac) 2
· 4H 2 O (0.1 M) were first dissolved in distilled water (100 mL) and mixed well
with each other. Citric acid solution (0.3 M, 100 mL) was later slowly added to the
mixture at room temperature under constant magnetic stirring. The obtained mixture
was stirred overnight and then the solution was evaporated at 80 °C until the gel was
formed. The gel was subsequently dried and ground to obtain the precursor powder.
Finally, the precursor powder was further annealed at 375 °C for 2 h in air. (2) Firstly,
Ni(Ac) 2 · 4H 2 O (0.05 M) and Co(Ac) 2 · 4H 2 O (0.1 M) were dissolved in distilled
water (100 mL) and mixed well with each other. Then, an ethanol solution of oxalic
acid (0.15 M, 100 mL) was slowly added to the mixed solution at room temperature
under constant magnetic stirring. The obtained mixture was stirred overnight and
then the solution was evaporated at 80 °C until the gel was formed. Subsequently,
the gel was dried and ground to obtain the precursor powder. Lastly, the precursor
powder was further annealed at 320 °C for 2 h in air. (3) Ni(Ac) 2 · 4H 2 O (0.05 M)
and Co(Ac) 2 · 4H 2 O (0.1 M) were first dissolved in distilled water (100 mL) and
mixed well with each other. Meanwhile, EDTA (0.15 M) was dissolved in distilled
water (100 mL), and the ammonia was added dropwise to maintain the constant
pH at 6.5. Then, the former mixed solution was slowly added to the EDTA ammonium solution at room temperature under constant magnetic stirring and the constant
pH = 6.5 was maintained via dropwise addition of ammonia during this process. The
obtained mixture was stirred overnight and then the solution was evaporated at 80 °C
until the gel was formed. The gel was subsequently dried and ground to obtain the
precursor powder. Finally, the precursor powder was annealed for 2 h at 400 °C in
air. The chelating agent is a particularly important factor that affects the size of particles, the different pore structures and specific surface area of the NiCo 2 O 4 , thereby
leading to the distinctions of their electrochemical properties; such observations
are of fundamental importance allowing the tailoring of electrochemical properties
through careful choice of chelating agent.
NiO nanomaterials with three different morphologies were obtained via a sol-gel
method and their morphology-dependent supercapacitive performance was further
explored (Kim et al. reported) (Kim et al. 2013). The special three-dimensional (3D)
nanoflower-shaped NiO has the highest pore volume, thus manifesting the superior
supercapacitor properties. The nanopores in the flower-shaped nanostructures can
greatly improve the contact and transport of the electrolyte, allowing for more 3D
nanochannels in the NiO network, thus offering longer electron pathways.
When it comes to carbon material, graphene is worth mentioning. Twodimensional (2D) graphene, with carbon atoms bonded in a hexagonal lattice, has
attracted considerable attention within the scientific community for its outstanding
properties such as its electrical and thermal conductivity (1738 S m
−1 and ~5 ×
10
3 W m
−1 K
−1 respectively), intrinsic carrier mobility (>2 × 10
5 cm
2 V
−1 s
−1 ),
theoretical surface area (~2600 m
2 g
−1 ), mechanical strength (~118 GPa), and elastic
modulus (~1 TPa). Lim et al. have presented an approach for the ultrafast fabrication
5 Synthesis of Three-Dimensional Nanomaterials
(CA), oxalic acid (OA) as well as ethylenediamine tetraacetic acid (EDTA) explored
during the fabrication and the tested electrochemical and supercapacitor properties
(Zhu et al. reported) (Zhu et al. 2014) (1) Ni(Ac) 2 · 4H 2 O (0.05 M) and Co(Ac) 2
· 4H 2 O (0.1 M) were first dissolved in distilled water (100 mL) and mixed well
with each other. Citric acid solution (0.3 M, 100 mL) was later slowly added to the
mixture at room temperature under constant magnetic stirring. The obtained mixture
was stirred overnight and then the solution was evaporated at 80 °C until the gel was
formed. The gel was subsequently dried and ground to obtain the precursor powder.
Finally, the precursor powder was further annealed at 375 °C for 2 h in air. (2) Firstly,
Ni(Ac) 2 · 4H 2 O (0.05 M) and Co(Ac) 2 · 4H 2 O (0.1 M) were dissolved in distilled
water (100 mL) and mixed well with each other. Then, an ethanol solution of oxalic
acid (0.15 M, 100 mL) was slowly added to the mixed solution at room temperature
under constant magnetic stirring. The obtained mixture was stirred overnight and
then the solution was evaporated at 80 °C until the gel was formed. Subsequently,
the gel was dried and ground to obtain the precursor powder. Lastly, the precursor
powder was further annealed at 320 °C for 2 h in air. (3) Ni(Ac) 2 · 4H 2 O (0.05 M)
and Co(Ac) 2 · 4H 2 O (0.1 M) were first dissolved in distilled water (100 mL) and
mixed well with each other. Meanwhile, EDTA (0.15 M) was dissolved in distilled
water (100 mL), and the ammonia was added dropwise to maintain the constant
pH at 6.5. Then, the former mixed solution was slowly added to the EDTA ammonium solution at room temperature under constant magnetic stirring and the constant
pH = 6.5 was maintained via dropwise addition of ammonia during this process. The
obtained mixture was stirred overnight and then the solution was evaporated at 80 °C
until the gel was formed. The gel was subsequently dried and ground to obtain the
precursor powder. Finally, the precursor powder was annealed for 2 h at 400 °C in
air. The chelating agent is a particularly important factor that affects the size of particles, the different pore structures and specific surface area of the NiCo 2 O 4 , thereby
leading to the distinctions of their electrochemical properties; such observations
are of fundamental importance allowing the tailoring of electrochemical properties
through careful choice of chelating agent.
NiO nanomaterials with three different morphologies were obtained via a sol-gel
method and their morphology-dependent supercapacitive performance was further
explored (Kim et al. reported) (Kim et al. 2013). The special three-dimensional (3D)
nanoflower-shaped NiO has the highest pore volume, thus manifesting the superior
supercapacitor properties. The nanopores in the flower-shaped nanostructures can
greatly improve the contact and transport of the electrolyte, allowing for more 3D
nanochannels in the NiO network, thus offering longer electron pathways.
When it comes to carbon material, graphene is worth mentioning. Twodimensional (2D) graphene, with carbon atoms bonded in a hexagonal lattice, has
attracted considerable attention within the scientific community for its outstanding
properties such as its electrical and thermal conductivity (1738 S m
−1 and ~5 ×
10
3 W m
−1 K
−1 respectively), intrinsic carrier mobility (>2 × 10
5 cm
2 V
−1 s
−1 ),
theoretical surface area (~2600 m
2 g
−1 ), mechanical strength (~118 GPa), and elastic
modulus (~1 TPa). Lim et al. have presented an approach for the ultrafast fabrication