48
3 Synthesis of One-Dimensional Nanomaterials
nucleation site for the CNTs to grow. Vertically aligned CNT arrays could be grown
by thermal CVD method. A substrate (stainless steel, silicon, quartz, etc.) is coated
with a catalytic metal of Ni/Fe/Co layer. In general, the layer is Fe, and is deposited
via sputtering to a thickness of 1–5 nm. A 10–50 nm underlayer of alumina is put
down on the substrate. This imparts good interfacial and controllable wetting properties. The as-prepared CNTs always have impurities, for example, non-carbonaceous
impurities and other forms of carbon (fullerene, amorphous carbon, etc.). The impurities need to be removed to make use of the CNTs in applications. Graphene and CNTs
have attracted tremendous attention, because of their unique properties, such as environmental benignity, lower cost, and high electronic conductivity. Some studies have
shown that hybrid architectures built from graphene and 1D CNTs show improved
properties and synergistic effects as regards electronic devices and energy storage.
Furthermore, the chemical properties of sp
2 carbon materials could be further tailored
by introducing heteroatom doping, for instance, boron, nitrogen, phosphorus, and
sulfur. Consequently, Yu et al. have fabricated an N-doped CNT/graphene hybrid
structure by a solid-state growth process (Ding et al. 2015). They use dicyandiamide, glucose, and nickel foam as nitrogen sources, carbon source, and substrate,
respectively. The overall synthetic procedure of N-doped 3D CNT/graphene hybrid
structures is achieved in a two-step process as shown in Fig. 3.3h, i. The ruffly
graphene layers as the support of CNTs can clearly be observed in Fig. 3.3j–l,
showing that CNTs are rooted and well interconnected with the in situ produced
graphene layers. The nickel foam plays a bifunctional role in providing scaffold for
graphene deposition, and offering in situ generated nickel nanoparticles as catalyst
for CNT growth on graphene layers without any synthetical catalyst. Conclusively,
the hybrid architectures could show stable cyclability and superior rate capability as
cathode hosts for lithium-sulfur batteries.
In summary, 1D nanomaterials are widely studied for use in electrochemical
energy storage devices because of their relatively short path lengths for ion and electron transport and insertion/extraction, large specific surface areas, and facile strain
relaxation during electrochemical cycling. Furthermore, 1D-based nanostructures
have attracted much attention from both the research community and the commercial
sector worldwide. Much effort has been devoted to improving the electrochemical
performance and mechanical properties of 1D nanostructure, and future directions
and existing problems are as follows: (1) Nanoscale composite materials may have
higher electrochemical conductivity and specific capacitance. Composite nanostructures not only compensate for the disadvantages of the separate components but also
incorporate the advantages of all the constituents. Furthermore, the synergistic effects
of 1D nanomaterials metal and conducting polymers or carbon nanomaterials can
maximize the properties of different components, for example, to further improve
the conductivity of the metal oxide/sulfides materials. (2) The results of both theoretical calculations and experimental research have indicated that structural control and
interfacial modification can observably enhance the rate performance, cycling ability
and specific capacity of 1D metal oxide/sulfides. It is key to design the complex 1D
nanostructure (e.g., core–shell nanostructure, array architecture, branched structure,
3 Synthesis of One-Dimensional Nanomaterials
nucleation site for the CNTs to grow. Vertically aligned CNT arrays could be grown
by thermal CVD method. A substrate (stainless steel, silicon, quartz, etc.) is coated
with a catalytic metal of Ni/Fe/Co layer. In general, the layer is Fe, and is deposited
via sputtering to a thickness of 1–5 nm. A 10–50 nm underlayer of alumina is put
down on the substrate. This imparts good interfacial and controllable wetting properties. The as-prepared CNTs always have impurities, for example, non-carbonaceous
impurities and other forms of carbon (fullerene, amorphous carbon, etc.). The impurities need to be removed to make use of the CNTs in applications. Graphene and CNTs
have attracted tremendous attention, because of their unique properties, such as environmental benignity, lower cost, and high electronic conductivity. Some studies have
shown that hybrid architectures built from graphene and 1D CNTs show improved
properties and synergistic effects as regards electronic devices and energy storage.
Furthermore, the chemical properties of sp
2 carbon materials could be further tailored
by introducing heteroatom doping, for instance, boron, nitrogen, phosphorus, and
sulfur. Consequently, Yu et al. have fabricated an N-doped CNT/graphene hybrid
structure by a solid-state growth process (Ding et al. 2015). They use dicyandiamide, glucose, and nickel foam as nitrogen sources, carbon source, and substrate,
respectively. The overall synthetic procedure of N-doped 3D CNT/graphene hybrid
structures is achieved in a two-step process as shown in Fig. 3.3h, i. The ruffly
graphene layers as the support of CNTs can clearly be observed in Fig. 3.3j–l,
showing that CNTs are rooted and well interconnected with the in situ produced
graphene layers. The nickel foam plays a bifunctional role in providing scaffold for
graphene deposition, and offering in situ generated nickel nanoparticles as catalyst
for CNT growth on graphene layers without any synthetical catalyst. Conclusively,
the hybrid architectures could show stable cyclability and superior rate capability as
cathode hosts for lithium-sulfur batteries.
In summary, 1D nanomaterials are widely studied for use in electrochemical
energy storage devices because of their relatively short path lengths for ion and electron transport and insertion/extraction, large specific surface areas, and facile strain
relaxation during electrochemical cycling. Furthermore, 1D-based nanostructures
have attracted much attention from both the research community and the commercial
sector worldwide. Much effort has been devoted to improving the electrochemical
performance and mechanical properties of 1D nanostructure, and future directions
and existing problems are as follows: (1) Nanoscale composite materials may have
higher electrochemical conductivity and specific capacitance. Composite nanostructures not only compensate for the disadvantages of the separate components but also
incorporate the advantages of all the constituents. Furthermore, the synergistic effects
of 1D nanomaterials metal and conducting polymers or carbon nanomaterials can
maximize the properties of different components, for example, to further improve
the conductivity of the metal oxide/sulfides materials. (2) The results of both theoretical calculations and experimental research have indicated that structural control and
interfacial modification can observably enhance the rate performance, cycling ability
and specific capacity of 1D metal oxide/sulfides. It is key to design the complex 1D
nanostructure (e.g., core–shell nanostructure, array architecture, branched structure,