4.1 2D Transition Metal Dichalcogenides
57
and pressed into a wafer with a fixed size by a pressing machine. Subsequently, a
thermal treatment is performed at 800 °C under argon atmosphere, and then the
resultant wafer is employed as anode and exfoliated in an electrolysis cell with platinum sheets as cathode, ammonium sulfate solution as the electrolyte. At a constant
voltage of 5 V, 2D MoS 2 -G hybrid is simultaneously and gradually exfoliated from
the resultant MoS 2 -graphite wafer. Finally, 2D MoS 2 -G hybrid can be facilely gained
since they are well dispersed in various solvents even after a few days. The resulting
products of 2D MoS 2 -G hybrid can be directly filtrated to flexible films through a
polypropylene separator membrane with a pore size of 0.22 μm (Fig. 4.1b–d).
Xie et al. (2015), by taking MoS 2 as a typical example, established the correlations between the 2D heterointerface and the sodium-ion storage performance
of layered metal sulfides/graphene composites. MoS 2 /reduced graphene oxide
(RGO) nanocomposites were synthesized via a simple hydrothermal method using
L-cysteine, phosphomolybdic acid, and GO as precursors. The sheet-on-sheet
MoS 2 /RGO nanocomposites were formed, which effectively suppresses agglomeration of MoS 2 and RGO. However, in order to realize the functionalities of the 2D
MoS 2 /RGO heterointerface, it is required to prepare high-quality electrical contact
between MoS 2 and RGO. The final MoS 2 /RGO composites with sheet-on-sheet structure and controllable heterointerfaces were fabricated by a hydrothermal preparation,
and the products underwent a calcination process after that. The in situ hybridization
of MoS 2 and RGO plays an important role in constructing MoS 2 /RGO heterostructures with enhanced electrochemical performances for Na
+ storage. First, RGO as
macromolecular surfactants can effectively stabilize MoS 2 nanosheets with high
surface energy, realizing high-dispersive MoS 2 supported on RGO. As a result, more
reactive sites are available for the electrode/electrolyte interaction. Second, this soft
integration method enables high-quality electrical contact between MoS 2 and RGO,
which ensures the functionality of the MoS 2 /RGO heterointerface for Na-ion storage
performance.
4.1.2 MoSe 2
Molybdenum diselenide (MoSe 2 ) structure possesses three atom layers in which
molybdenum atom is sandwiched between two selenium atoms, i.e., strong covalent bond characterized the interaction of Se-Mo-Se. On the other hand, interactions between individual layers of MoSe 2 are characterized via weak Van der Waals
force which is facilitating ion intercalation/deintercalation path during electrochemical charge storage process. In addition, MoSe 2 has high theoretical capacity and is
embraced of low-cost and abundant elements.
Generally, few-layered MoSe 2 nanosheets are synthesized via a chemical vapor
deposition (CVD) or rapid thermal processing preparation. However, when these
techniques are employed to synthesize a large amount of electrode materials, their
shortcomings of high-price and user-hostile cannot be ignored (Bachmatiuk et al.
2014; Mutlu et al. 2014; Xia et al. 2014). Few-layered MoSe 2 nanosheets have
57
and pressed into a wafer with a fixed size by a pressing machine. Subsequently, a
thermal treatment is performed at 800 °C under argon atmosphere, and then the
resultant wafer is employed as anode and exfoliated in an electrolysis cell with platinum sheets as cathode, ammonium sulfate solution as the electrolyte. At a constant
voltage of 5 V, 2D MoS 2 -G hybrid is simultaneously and gradually exfoliated from
the resultant MoS 2 -graphite wafer. Finally, 2D MoS 2 -G hybrid can be facilely gained
since they are well dispersed in various solvents even after a few days. The resulting
products of 2D MoS 2 -G hybrid can be directly filtrated to flexible films through a
polypropylene separator membrane with a pore size of 0.22 μm (Fig. 4.1b–d).
Xie et al. (2015), by taking MoS 2 as a typical example, established the correlations between the 2D heterointerface and the sodium-ion storage performance
of layered metal sulfides/graphene composites. MoS 2 /reduced graphene oxide
(RGO) nanocomposites were synthesized via a simple hydrothermal method using
L-cysteine, phosphomolybdic acid, and GO as precursors. The sheet-on-sheet
MoS 2 /RGO nanocomposites were formed, which effectively suppresses agglomeration of MoS 2 and RGO. However, in order to realize the functionalities of the 2D
MoS 2 /RGO heterointerface, it is required to prepare high-quality electrical contact
between MoS 2 and RGO. The final MoS 2 /RGO composites with sheet-on-sheet structure and controllable heterointerfaces were fabricated by a hydrothermal preparation,
and the products underwent a calcination process after that. The in situ hybridization
of MoS 2 and RGO plays an important role in constructing MoS 2 /RGO heterostructures with enhanced electrochemical performances for Na
+ storage. First, RGO as
macromolecular surfactants can effectively stabilize MoS 2 nanosheets with high
surface energy, realizing high-dispersive MoS 2 supported on RGO. As a result, more
reactive sites are available for the electrode/electrolyte interaction. Second, this soft
integration method enables high-quality electrical contact between MoS 2 and RGO,
which ensures the functionality of the MoS 2 /RGO heterointerface for Na-ion storage
performance.
4.1.2 MoSe 2
Molybdenum diselenide (MoSe 2 ) structure possesses three atom layers in which
molybdenum atom is sandwiched between two selenium atoms, i.e., strong covalent bond characterized the interaction of Se-Mo-Se. On the other hand, interactions between individual layers of MoSe 2 are characterized via weak Van der Waals
force which is facilitating ion intercalation/deintercalation path during electrochemical charge storage process. In addition, MoSe 2 has high theoretical capacity and is
embraced of low-cost and abundant elements.
Generally, few-layered MoSe 2 nanosheets are synthesized via a chemical vapor
deposition (CVD) or rapid thermal processing preparation. However, when these
techniques are employed to synthesize a large amount of electrode materials, their
shortcomings of high-price and user-hostile cannot be ignored (Bachmatiuk et al.
2014; Mutlu et al. 2014; Xia et al. 2014). Few-layered MoSe 2 nanosheets have