**6.2 Carbon-WS2 composite electrode materials**

*Novel Nanomaterials*

together through Vander Waals force in such a way that transition metal layer is present in between the two chalcogen sheets [67]. On the basis of crystal structure, there are two types of phases of TMDs, which are metallic 1T phase with an octahedral structure and semiconducting 2H phase with a trigonal structure. Recently, TMDs have been attracted great attention as SC electrode materials due to their large surface area, low cost, variable oxidation states, high mechanical properties, high chemical stability and easy synthesis [68]. The variable oxidation states, large surface area, and active edges of TMDs allow electrical double layer and fast/reversible redox charge storage mechanisms and offer high energy storage capability in SCs. However, due to the inherently low conductivity, poor cycle life, large volume change during cycling and restacking limits their electrochemical performance as SC electrodes [69]. For example, Soon *et al.* has synthesized sheet-like morphology of MoS2 by chemical vapor deposition method, which has a very large surface area favorable for double layer storage. But due to its poor electrical conductivity, it showed low specific capacitance of ∼100 F g−1 at a scan rate of 1 mV s−1 [70]. Therefore, in order to improve the electrochemical performance of TMDs, they have been compositing with highly conducting/electroactive carbon based supporting materials by various top-down/bottom-up and both synthetic approaches. The synergic effect of carbon-TMDs based composite materials such as carbon offers conductive channels and increasing the interfacial contact, whereas TMDs provide a short ion diffusion path and followed by short electron transport path enhances

MoS2/MWCNT nanocomposite synthesized by a hydrothermal method exhibited a large surface area and fast ionic transport properties and showed a high specific capacitance of 452.7 F g−1 with good cycling stability (95.8% retention after 1000 cycles), which is almost three times larger than the bare MoS2 (149.6 to 452.7 F g−1) [71]. Ali *et al.* fabricated MoS2/graphene composite from bulk MoS2 and graphite rod through facile electrochemical exfoliation method and exhibited high specific capacitance of 227 F g−1 as compared with the exfoliated MoS2 (70 F g−1) and exfoliated graphene (85 F g−1) at a current density of 0.1 A g−1 [72]. The high specific capacitance of MoS2/graphene composite is due to the synergistic effect between MoS2 and graphene. Ali *et al.* demonstrated the electrochemical performance of MoS2/CNT/GNF composite and compared the performance with MoS2/CNTs, MoS2/graphene nanoflakes [73]. It has been noticed that the electrochemical charge storage performance has been improved by incorporation of the carbon materials into the composite and the composite showed a maximum specific capacitance of 104 F g−1 at a current density of 0.5 A g−1 with capacitance retention of 75% after the 1000 cycle at a scan rate of 10 mV/s. Another interesting MoS2 rGO/MWCNT fiber electrode was fabricated by incorporating rGO nanosheets and MoS2 into aligned MWCNT, which operated at a stable potential window of 1.4 V and exhibited high coulombic efficiency of 100% over 7000 cycles in the bending state (**Figure 7(b-f )**) [74]. Zhang *et al.* reported an agarose induced technique to synthesize MoS2/carbon composite aerogel, which showed a high specific capacitance of 712.6 F g−1 at a current density of 1 A g−1 with cyclic stability of 97.3% over 13000 charge-discharge cycles (**Figure 7(g-j)**) [75]. The high specific capacitance of MoS2/carbon composite aerogel is because of 3D intercalated network with hierarchal porous and interlayer MoS2 expanded structures, which were beneficial for easy ion transportation. 3D graphene/MoS2 composite electrode material has been synthesized by Sun et al and co-workers through a simple and facile one-step hydrothermal process [76]. The as-synthesized composite electrode exhibited

the overall electrochemical performance of the SC.

**6.1 Carbon-MoS2 composite electrode materials**

**130**

WS2 nanoplates supported on carbon fiber cloth (WS2/CFC) have been synthesized by a facile solvothermal process and used as electrode material for SC [77]. The 3D network of CFC not only prevent the agglomeration of WS2 nanoplates but also enhances the ion transport efficiency due to low charge transfer resistance (Rct) of 0.1 Ω. The as fabricated WS2/CFC electrode exhibited a high specific capacitance of 399 F g−1 at 1 A g−1 current density with cyclic retention of 99% over charge-discharge 500 cycles, which is higher than compared with bare WS2. In addition, developing such composite of WS2 with the carbon fibre helps for fabricating wearable SCs which are in demand for wearable electronics. Yang *et al.* fabricated WS2@CNT hybrid film electrode by incorporating conducting CNTs into WS2. The WS2@CNT hybrid film with a unique skeleton structure showed a maximum specific area capacitance of 752.53 mF cm−2 at a scan rate 20 mV s−1 with very good cyclic stability by only loss of 1.28% capacitance after 10,000 cycles. In addition, a quasi-solid-state flexible SC made by WS2@CNT hybrid film exhibited excellent bendability under bending to 135 10, 000 times with the loss of 23.12% at scan rate of 100 mV s−1 [53]. Tu *et al.* have been synthesized WS2/RGO hybrid material by using a simple molten salt process, which showed a high specific capacitance of 2508.07 F g−1 at 1 mV s−1 scan rate with excellent capacitance retention of 98.6% over 5000 cycles, due to synergic effect of highly conducting RGO and large charge-accumulating sites of WS2 networks. Likewise, Xu *et al.* demonstrated 3D composite of WS2 nanoflakes and quantum dots on N and S co-doped reduced graphene oxide (WS2/N,S-rGO) crumpled nanosheets through a rapid solution combustion synthesis of the precursor and subsequent gas-solid phase sulfurization process, which presented a significant specific capacitance of 1562.5 F g−1 at 1 A g−1 current density, and a rate capability of 780 F g−1 at 40 A g−1 (**Figure 8(a-c)**) [78]. The high specific capacitance of WS2/N,S-rGO hybrids is because of synergistic effect between WS2 and N,S-rGO, where N,S-rGO provides larger contact surface area, excellent charge transport, and shorter ion diffusion path. Hierarchical MoSe2/C hybrid was successfully fabricated by facile one-step hydrothermal strategy, which composed of few-layered MoSe2 nanosheets and amorphous carbon obtained from the decomposition of the triethylene glycol. As fabricated hierarchical MoSe2/C electrode exhibited high specific capacitance of 878.6 F g−1 in comparison with the bare MoSe2 at current density of 1 A g−1 and maintained 98% of initial capacitance over 2000 cycles without obvious decrease. The superior electrochemical performances of MoSe2/C hybrid can be ascribed to hierarchical structure of MoSe2 and conducting nature of carbon, which help for providing large surface area for electrochemical reactions and enhancing charge carriers transfer at the electrolyte/electrode interface [79]. Liu *et al.* fabricated VACNTF@MoSe2/NF composite electrode through a combined chemical vapor deposition method and solvothermal methods by growing MoSe2 nanoflakes on the vertically aligned carbon nanotube array film (VACNTF) with binder-free nickel foam as current collector [80]. The as fabricated VACNTF@MoSe2/NF composite electrode exhibited high specific capacitance of 435 F g−1 at a current density of 1 A g−1 with outstanding cycling stability

#### **Figure 8.**

*(a) Schematic illustration of synthetic processes of WS2/N,S-rGO hybrid, (b) HRTEM, STEM and EDS elemental mapping images of WS2/N,S-rGO hybrid, and (c) The specific capacitances of the WS2, N,S-rGO and WS2/N,S-rGO hybrid at different current densities [78]. (d) Schematic illustration of the synthesis process of the VACNTF@MoSe2/NF composite electrode, (e) SEM images of the VACNTF@MoSe2 composites (inset: high magnification), and (f) The specific capacitance comparison of the MoSe2/NF, VACNTF/NF and VACNTF@MoSe2/NF electrodes at various current densities [80]. (g) Specific capacitance of the MoSe2 NS and MoSe2/G nanohybrid based electrodes as a function of current density, and (h) Ragone plot for the MoSe2G||AC ASC device (inset: photograph of ASC device) [81].*

of 92% after 5000 cycles (**Figure 8(d-f )**). In addition, the VACNTF@MoSe2/NF composite based ASC displays a high energy density with 22 W h kg−1 for a power density of 330 W kg−1. Kirubasankar *et al.* MoSe2/graphene nanohybrid based electrode prepared by a simple and facile sonochemical route, which showed higher specific capacitance (945 F g−1) as compared to MoSe2 nanosheets (576 F g−1) at 1 A g−1 current density. Further, as fabricated ASC device based on MoSe2/ graphene nanohybrid retains 88% of its capacitance over 3000 cycles and delivers an energy density of 26.6 W h kg−1 at a power density of 0.8 kW kg−1 (**Figure 8(g, h)**) [81]. The high specific capacitance with better rate capability is due to the effective penetration and migration of electrolyte, reduction of the contact resistance and shortness of the diffusion path of ions between the electrode-electrolyte interface, which enhances the redox kinetics and provide maximum utilization of the electroactive area, so providing a high structural stability during charge-discharge processes. Similarly, Huang *et al*. demonstrated MoSe2/ graphene on flexible Ni electrode, which could deliver a specific capacitance of 1422 F g−1and fully retention of initial capacitance over 1500 cycles [82]. Wei *et al*. first time fabricated free-standing SC anode based on 3D MoSe2 nanoflowers (MoSe2 NFs) and hierarchically porous anisotropic carbonized delignified wood (CDW), which exhibited ultrahigh capacitance of 1043 mF cm−2 at a current density of 1 mA cm−2 and excellent cycling stability less than 5% capacitance loss over 5000 cycles. The ASC device was made by integration of 3D MoSe2 NFs@CDW anode and a common MnO2-based cathode, which exhibited a high capacitance of 415 mF cm−2 at a current density of 2.5 mA cm−2 with high energy density of 147 mW h cm−2 at power density of 2 mW cm−2. These results confirm that 3D MoSe2 NFs@CDW based anode can be used as a potential anode for the development of high-performance SCs [83].

**133**

**Author details**

Prasanta Kumar Sahoo1

**Acknowledgements**

University, Bhubaneswar, Odisha, India

provided the original work is properly cited.

, Chi-Ang Tseng2

Taiwan, under grant numbers 107-2113-M-845-001-MY3.

, Yi-June Huang3

1 Department of Mechanical Engineering, Siksha 'O' Anusandhan, Deemed to be

This work was supported by the Ministry of Science and Technology (MOST) of

2 Department of Chemistry, National Taiwan University, Taipei, Taiwan

Biomedical Engineering, Taipei Medical University, Taipei, Taiwan

\*Address all correspondence to: CPLee@utaipei.edu.tw

3 Graduate Institute of Nanomedicine and Medical Engineering, College of

4 Department of Applied Physics and Chemistry, University of Taipei, Taiwan

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

and Chuan-Pei Lee4

\*

*Carbon-Based Nanocomposite Materials for High-Performance Supercapacitors*

In the past few decades, SCs have been extensively studied as energy storage devices and more focusing area in the multidisciplinary science over the world. The selection of high performance SC electrode materials based on high specific capacitance, low internal resistance and good stability. In this article, we have reviewed the carbon-based composite materials (*i.e.*, metal oxide, metal hydroxide, TMDs composited with carbon materials) as promising SC electrode materials due to the synergic effect of the composite materials such as high surface area, interconnected porous structure, high electrical conductivity, excellent wettability towards the electrolyte, and presence of electrochemically active surface functionalities of the carbon supports which improves the EDL capacitance while metal oxide or metal hydroxide or TMDs enhances electrochemical performance through pseudocapacitive/faradaic charge-storage process. The carbon-based composite materials demonstrated herein usually possesses high specific capacity, impressive energy density and maintain long term stability with better mechanical flexibility. We also observe the microstructural changes in the carbon-based composite materials would be more favorable for fabrication of high performance supercapacitor. We also explained how the composite materials overcome the traditional obstacles while formulating the standard electrode designs as compare to individual components.

*DOI: http://dx.doi.org/10.5772/intechopen.95460*

**7. Conclusion**

*Carbon-Based Nanocomposite Materials for High-Performance Supercapacitors DOI: http://dx.doi.org/10.5772/intechopen.95460*
