62
4 Synthesis of Two-Dimensional (2D) Nanomaterials
this work, the MnO 2 nanosheets have been planted merely on a side of the graphene
film without any binders. It’s well known that active materials, current collector and
binder are essential parts for fabricating a supercapacitor. In the MGF, the large
specific surface provided by the grapheme film makes the usage of the large pseudocapacitance of MnO 2 possible. At the same time, the graphene film also acts as a fast
electrotransport current collector without binders. The MnO 2 nanosheets vertically
align on the graphene surface forming an open porous structure. Therefore, the MnO 2
surface electrons have a much shorter distance to cross to the current collector. As a
result, the interface between the electrolyte and the MnO 2 -graphene film electrode
increased greatly. Experimental results showed that for the flexible MGF with an
excellent capacitance of 280 F g
−1 at 1 A g
−1 , after 10,000 cycles the capacitance
content is 99%. Further studies showed that a flexible MGF applied symmetric supercapacitor has provided a 77 F g
−1 capacitance at 1 A g
−1 , the capacitance content was
still at 91% after 10,000 cycles, and the energy density was 10.7 W h kg
−1 at a power
density of 500 W kg
−1 . Figure 4.2i illustrates the preparation of MGF by spin-coating
and hydrothermal process. Figure 4.2j shows the MnO 2 nanosheets vertically grew
along the grapheme surface and constructed a porous network structure. The cross
section of MGF is showed in Fig. 4.2k.
Mn 2 O 3 has presented the good pseudocapacitor electrode materials because of
its high specific capacity (Reddy et al. 2010). Furthermore, Mn 2 O 3 -based electrodes
also have low operating voltages, i.e., the average charge and discharge voltages
of 1.2 and 0.5 V, respectively (Deng et al. 2014). Over Mn 2 O 3 nanoparticles, the
nanosheets structures are displayed high surface to volume ratio, big pores, and pore
volume, which can accelerate the ions transportation, leading to excellent supercapacitor performance. Li et al. (2017c) present highly dense and uniform Mn 2 O 3
nanowalls thin films grown on the Ni foam through hydrothermal process and used as
electroactive electrode for the fabrication of electrochemical supercapacitors. From
the cyclic voltammetry (CV) results, it has been found that Mn 2 O 3 nanowalls-based
electrode displays excellent specific capacitance of 480 F g
−1 at 10 mV s
−1 . The
specific capacitance of 461 F g
−1 at 0.5 A g
−1 with excellent recyclability is evaluated
by galvanostat discharge-charge measurements.
4.2.3 Fe 3 O 4
Among numerous materials advocated as promising anode candidates, Fe 3 O 4
attracts extensive interest owing to its nontoxicity, good lithium storage capacity
(928 mA h g
−1 ), ecofriendliness, natural abundance, and low cost (Guo et al. 2010;
Mitchell et al. 2014). Despite these predominant features, their disadvantages such as
sluggish kinetics, agglomeration, severe volume variation (∼90%), and low intrinsic
electric conductivity during the conversion reaction process, lead to the loss of electrical contact from the current collector and dramatic electrode pulverization, thus
resulting in poor cyclic properties (Tuˇ cek et al. 2014; Poizot et al. 2010).
4 Synthesis of Two-Dimensional (2D) Nanomaterials
this work, the MnO 2 nanosheets have been planted merely on a side of the graphene
film without any binders. It’s well known that active materials, current collector and
binder are essential parts for fabricating a supercapacitor. In the MGF, the large
specific surface provided by the grapheme film makes the usage of the large pseudocapacitance of MnO 2 possible. At the same time, the graphene film also acts as a fast
electrotransport current collector without binders. The MnO 2 nanosheets vertically
align on the graphene surface forming an open porous structure. Therefore, the MnO 2
surface electrons have a much shorter distance to cross to the current collector. As a
result, the interface between the electrolyte and the MnO 2 -graphene film electrode
increased greatly. Experimental results showed that for the flexible MGF with an
excellent capacitance of 280 F g
−1 at 1 A g
−1 , after 10,000 cycles the capacitance
content is 99%. Further studies showed that a flexible MGF applied symmetric supercapacitor has provided a 77 F g
−1 capacitance at 1 A g
−1 , the capacitance content was
still at 91% after 10,000 cycles, and the energy density was 10.7 W h kg
−1 at a power
density of 500 W kg
−1 . Figure 4.2i illustrates the preparation of MGF by spin-coating
and hydrothermal process. Figure 4.2j shows the MnO 2 nanosheets vertically grew
along the grapheme surface and constructed a porous network structure. The cross
section of MGF is showed in Fig. 4.2k.
Mn 2 O 3 has presented the good pseudocapacitor electrode materials because of
its high specific capacity (Reddy et al. 2010). Furthermore, Mn 2 O 3 -based electrodes
also have low operating voltages, i.e., the average charge and discharge voltages
of 1.2 and 0.5 V, respectively (Deng et al. 2014). Over Mn 2 O 3 nanoparticles, the
nanosheets structures are displayed high surface to volume ratio, big pores, and pore
volume, which can accelerate the ions transportation, leading to excellent supercapacitor performance. Li et al. (2017c) present highly dense and uniform Mn 2 O 3
nanowalls thin films grown on the Ni foam through hydrothermal process and used as
electroactive electrode for the fabrication of electrochemical supercapacitors. From
the cyclic voltammetry (CV) results, it has been found that Mn 2 O 3 nanowalls-based
electrode displays excellent specific capacitance of 480 F g
−1 at 10 mV s
−1 . The
specific capacitance of 461 F g
−1 at 0.5 A g
−1 with excellent recyclability is evaluated
by galvanostat discharge-charge measurements.
4.2.3 Fe 3 O 4
Among numerous materials advocated as promising anode candidates, Fe 3 O 4
attracts extensive interest owing to its nontoxicity, good lithium storage capacity
(928 mA h g
−1 ), ecofriendliness, natural abundance, and low cost (Guo et al. 2010;
Mitchell et al. 2014). Despite these predominant features, their disadvantages such as
sluggish kinetics, agglomeration, severe volume variation (∼90%), and low intrinsic
electric conductivity during the conversion reaction process, lead to the loss of electrical contact from the current collector and dramatic electrode pulverization, thus
resulting in poor cyclic properties (Tuˇ cek et al. 2014; Poizot et al. 2010).