58
4 Synthesis of Two-Dimensional (2D) Nanomaterials
been large-scale synthesized by Balasingam et al. (2015) via a simple hydrothermal
method, and aqueous electrolyte (H 2 SO 4 ) was used to measure their electrochemical
capacitance under a symmetric cell configuration with two electrodes. The maximal
specific capacitance was 199 F g
−1 , which was obtained at a scan rate of 2 mV s
−1 .
Furthermore, for the long-term stability test, the capacitance of prepared electrode
maintained nearly 75% of its original capacitance after working over 10,000 cycles,
which showed it as a suitable material for electrochemical capacitors (Fig. 4.1e, f).
4.1.3 WS 2
Similar to graphene, tungsten disulfide (WS 2 ) is believed as another promising material for electrochemistry. However, in order to enhance the practicability of this material, a sophisticated synthesis that can control its morphology is required. Fortunately,
a facile synthesis method has been proposed by Qian et al. (2016), which could fabricate WS 2 nanostructures with different morphologies. In the synthesis routes, WO 3
and S powders underwent thermal evaporation directly onto Si substrates, which were
sputtered with W film. During the process, not only nanostructured W-contained
precursors were not needed, but also toxic sulfide gases would not be mentioned.
A schematic is presented in Fig. 4.1g. Interestingly, large quantities of horizontally
grown WS 2 nanoplates, pure hexagonal, nanoplate formed flowers, and vertically
grown nanoplates can be obtained by this preparation, which is realized simply by
controlling the distance between the substrate and source powders.
WS 2 is widely considered to be a suitable material for charge accumulation, which
thanks to its extensive active sites existing in the spacing between 2D structures and
the interspacing of atomic layer, furthermore, the Faradaic reactions generated extra
charges on the tungsten centers, which also matter. However, the restacking between
the nanosheets and the low electronic conductivity as well as the relative brittle
of WS 2 limits its adhibition. To overcome this difficulty, highly conductive carbon
materials were applied to enhance the conductivity of the electrode and meanwhile
prevent the restacking of WS 2 (Liu et al. 2014; Hu et al. 2013). Tu et al. (2016)
reported a supercapacitor electrode based on a 2D hybrid consisting of WS 2 and
RGO nanostructures fabricated by using a simple molten salt process. Figure 4.1h
presents the HRTEM image for the WS 2 nanomaterial. The SEM images for the
WS 2 , RGO, and the WS 2 /RGO hybrid were shown in Fig. 4.1i–k, respectively. To
distinguish the WS 2 and RGO nanostructures more clearly, the TEM image for the
WS 2 /RGO was obtained as shown in Fig. 4.1l. A surprising high specific capacitance
of 1355.67 F g
−1 was achieved for WS 2 /RGO hybrid-based supercapacitor electrode
at the scan rate of 1 mV s
−1 . Considering that WS 2 has the advantage of large chargeaccumulating sites that located on the 2D planes, while RGO stands out among other
materials for its excellent conductivity and superior connections in the networks
structure of WS 2 , the synergic effect between them can be the explanation for prominent capacitance of the supercapacitor electrodes. Moreover, the WS 2 /RGO-based
electrode achieves 98.6% retention of the original capacitance after 5000 cycles,
4 Synthesis of Two-Dimensional (2D) Nanomaterials
been large-scale synthesized by Balasingam et al. (2015) via a simple hydrothermal
method, and aqueous electrolyte (H 2 SO 4 ) was used to measure their electrochemical
capacitance under a symmetric cell configuration with two electrodes. The maximal
specific capacitance was 199 F g
−1 , which was obtained at a scan rate of 2 mV s
−1 .
Furthermore, for the long-term stability test, the capacitance of prepared electrode
maintained nearly 75% of its original capacitance after working over 10,000 cycles,
which showed it as a suitable material for electrochemical capacitors (Fig. 4.1e, f).
4.1.3 WS 2
Similar to graphene, tungsten disulfide (WS 2 ) is believed as another promising material for electrochemistry. However, in order to enhance the practicability of this material, a sophisticated synthesis that can control its morphology is required. Fortunately,
a facile synthesis method has been proposed by Qian et al. (2016), which could fabricate WS 2 nanostructures with different morphologies. In the synthesis routes, WO 3
and S powders underwent thermal evaporation directly onto Si substrates, which were
sputtered with W film. During the process, not only nanostructured W-contained
precursors were not needed, but also toxic sulfide gases would not be mentioned.
A schematic is presented in Fig. 4.1g. Interestingly, large quantities of horizontally
grown WS 2 nanoplates, pure hexagonal, nanoplate formed flowers, and vertically
grown nanoplates can be obtained by this preparation, which is realized simply by
controlling the distance between the substrate and source powders.
WS 2 is widely considered to be a suitable material for charge accumulation, which
thanks to its extensive active sites existing in the spacing between 2D structures and
the interspacing of atomic layer, furthermore, the Faradaic reactions generated extra
charges on the tungsten centers, which also matter. However, the restacking between
the nanosheets and the low electronic conductivity as well as the relative brittle
of WS 2 limits its adhibition. To overcome this difficulty, highly conductive carbon
materials were applied to enhance the conductivity of the electrode and meanwhile
prevent the restacking of WS 2 (Liu et al. 2014; Hu et al. 2013). Tu et al. (2016)
reported a supercapacitor electrode based on a 2D hybrid consisting of WS 2 and
RGO nanostructures fabricated by using a simple molten salt process. Figure 4.1h
presents the HRTEM image for the WS 2 nanomaterial. The SEM images for the
WS 2 , RGO, and the WS 2 /RGO hybrid were shown in Fig. 4.1i–k, respectively. To
distinguish the WS 2 and RGO nanostructures more clearly, the TEM image for the
WS 2 /RGO was obtained as shown in Fig. 4.1l. A surprising high specific capacitance
of 1355.67 F g
−1 was achieved for WS 2 /RGO hybrid-based supercapacitor electrode
at the scan rate of 1 mV s
−1 . Considering that WS 2 has the advantage of large chargeaccumulating sites that located on the 2D planes, while RGO stands out among other
materials for its excellent conductivity and superior connections in the networks
structure of WS 2 , the synergic effect between them can be the explanation for prominent capacitance of the supercapacitor electrodes. Moreover, the WS 2 /RGO-based
electrode achieves 98.6% retention of the original capacitance after 5000 cycles,