**4. Fullerene**

Fullerenes or Buckyballs are a novel class of carbon nanomaterials. The basic elements of fullerenes are called isomers. Their homologs range from the lower homologs that have received the most attention, such as C60 and C70, to higher fullerenes, such as C240, C540, and C720. They have shown to be valuable in various scientific domains, including separating and identifying different chemical species. Fullerene was first produced by Kroto, Curl, and Smalley via laser-induced evaporation of graphite. As a result, the discovery of Buckminsterfullerene, also known as C60, resulted from a research study that connected synthetic chemistry, microwave spectroscopy, and radio-astronomy. Fullerene was born from the search to reproduce poly acetylenes discovered in interstellar space [33].

Fullerenes have a structure composed of sp2 carbons with distinct chemical and physical characteristics and a highly symmetrical cage with varying widths *Carbon Nanomaterials Based Supercapacitors: Recent Trends DOI: http://dx.doi.org/10.5772/intechopen.106730*

(C60, C76, etc.) [34]. Thanks to their excellent electrochemical stability, small size, unique shape, and well-ordered structure [35], they enable their use in energy conversion systems.

Thanks to their excellent electrochemical stability, small size, unique shape, and well-ordered structure, they enable their use in energy conversion systems. Fullerenes' distinctive 0D structure makes them valuable building blocks for supramolecular assemblies and micro/nano functional materials used in drug delivery [36], photovoltaic devices [37], optoelectronics [38], sensors [39], catalysis [40], and other fields.

The fullerene molecule C60, which has a structure of 60 carbon atoms, 12 pentagonal C5-C5 single bonds, and C5 = C6 double bonds (20 hexagons), is the most often employed in supercapacitors. The following are some studies on the importance of fullerene in supercapacitor manufacture.

Activated fullerene (A-C60) decorated over zinc cobaltite (A-C60-ZCO) has been synthesized by a solvothermal approach as a supercapacitor electrode [41]. The greater enclosed area of the CV and the well-defined redox peaks suggest that A-C60-ZCO has a high specific capacitance and a strong pseudo capacitive nature. It was reported that the specific capacitance value is better for the 10 wt.% of A-C60 in ZCO loading than for the 2, 5, and 15 wt.% loadings. So, a composite with 10 wt.% A-C60 loading is the best for further electrochemical studies [41]. The character of the CV curve of A-C60-ZCO stays the same, except for a shift in peak position even at a higher scan rate (100 mV/s), indicating that the as manufactured material possesses rapid and reversible faradic performance. At scan speeds of 1, 5, 10, 20, 40, 50, 70, and 100 mV/sec, the A-C60-ZCO has volumetric specific capacitances of 593.2, 554.18, 506.2, 412.3, 332.7, 296.584, 260.696, 221.76 F/g. With an increase in scan rate, specific capacitance decreases as internal resistance becomes more dominant. The pseudocapacitive character of the active material is firmly confirmed by all GCD curves, resembling separate plateau areas compared to CV curves. Because of the partial ion migration toward the core of the active material, which may be controlled by limiting the loading quantity of active material, the specific capacitance value at higher current densities shows a small decline.

Under the same current density, -C60-ZCO has the longest charge/discharge time among ZCO, A-C60, and C60, indicating that A-C60-ZCO has the highest specific capacitance. At a current density of 2 A/g, the specific capacitance of A-C60-ZCO, ZCO, A-C60, and C60 electrodes is determined to be 269.81, 124.05, 34.41, and 24.18 F/g, respectively. The synergistic impact of the pseudo capacitive ZCO and A-C60 increases specific capacitance. All of the GCD curves have plateaus, which is strong evidence that the active material is pseudo capacitive and consistent with CV curves. The calculated specific capacitance values were 269.81, 144.36, 106.53, 84.06, 33.03, 27.89, 23.11, and 19.56 F/g at a current density of 2, 3, 4, 5, 7, 8, 9, and 10 F/g respectively.

In another work, a composite from polyaniline (PANI)/fullerene derivative (PCBM) Phenyl-C60-butyric acid methyl ester was constructed and tested as supercapacitor materials [42]. By varying the ratios of PCBM, different PANI/ PCBMx (where x = 0, 2.5, 5, and 10) were prepared. It was concluded that the PANI/PCBM electrodes had a higher specific capacitance than PANI due to the synergetic effect of PANI and PCBM. Also, it was found that the PANI/PCBM5 had the highest specific capacitance of 2609 F/g compared to 1216, 1882, and 1770 F/g for pure PANI, PANI/PCBM2.5, and PANI/PCBM10. The decreasing of specific capacitance of nanocomposite electrodes with PCBM content higher than 5 wt.% is ascribed to a larger size of PCBM, which decreases surface area.

#### *Updates on Supercapacitors*

3D pore structure produced C60 molecules into graphene sheets by hydrothermal approach to enhance their electrochemical performance [42]. The CV curves of mC60/graphene composite revealed the EDLC and pseudocapacitors. The electrochemical dependence on mass ratio, temperature, and reaction time was studied. It was found that typically when the mass ratio of C60 to GO is 1:8, reaction time is 12 hr., and temperature is 150oC, the specific capacitance reaches 332.3F/g compared to 215.1 F/g for pure reduced graphene oxide. It was concluded from GCD curves that the mass ratio of C60 to GO is 1:8 is the best for optimizing the composite charge/discharge performance. C60 molecules into graphene sheets by hydrothermal approach to enhance their electrochemical performance [43]. The CV curves of mC60/graphene composite revealed the EDLC and pseudocapacitors. The electrochemical dependence on mass ratio, temperature, and reaction time was studied. It was found that typically when the mass ratio of C60 to GO is 1:8, reaction time is 12 hr., and temperature is 150°C, the specific capacitance reaches 332.3F/g compared to 215.1 F/g for pure reduced graphene oxide. It was concluded from GCD curves that the mass ratio of C60 to GO is 1:8 is the best for optimizing the composite charge/ discharge performance.

A novel supercapacitor electrode was created using a carbon nanoonion(multilayer fullerene) /manganese dioxide/iron oxide (CNO/MnO2/Fe3O4) nanocomposite [44]. The electrochemical performance of prepared supercapacitors composed of MnO2, CNO, MnO2/Fe3O4, and CNO/MnO2/Fe3O4 nanocomposite was investigated. The rectangular shapes of CV curves of electrodes were established. The rise in super-capacitance of the CNO/MnO2/Fe3O4 electrode is due to the increased surface area of the CNO and the presence of MnO2 and Fe3O4, which increases the adsorption/desorption of cation and onion on the nanocomposite surface. The supercapacitive current of the CNO/MnO2/Fe3O4 was higher than metal oxides electrodes due to the presence of CNO with a high surface area. It was observed that the Metal oxide electrodes have less symmetry than those containing CNO. Furthermore, The CNO/MnO2/Fe3O4 nanocomposite electrode's longer discharge duration implies improved electrode quality. The calculated specific capacitance of CNO/MnO2/Fe3O4 electrodes was higher than other electrodes. At 1, 2, 3, and 4 A/g, CNO/MnO2/Fe3O4 had a specific capacitance of 1130, 972.50, 900, and 730 F/g, while MnO2/Fe3O4 had 571.25, 537.50, 442.50, and 400 F/g. Specific capacitances were 487.5 F/g at 1 A/g, 415 F/g at 2 A/g, 375 F/g at 3 A/g, and 340 F/g at 4 A/g for CNO. MnO2's capacitance at 1 to 4 A/g was 382.94, 326.14, 285.12, and 202.59 [44].

Using the stacking interactions of graphene with aromatic rings of functionalized fullerenes created and produced several unique graphene-based nanomaterials. To assure strong contacts and stable assembly of fullerenes on the surface of graphene, C60, C70, and Sc3N@C80 fullerene derivatives containing biphenyl, naphthalene, phenanthrene, or pyrene moieties were produced [45]. Graphene coated with bisnaphthalene C70 fullerene malonate (G-BN7) revealed a 15% higher capacitance than graphene before modification, with a specific capacitance value of 56.15 F/g. Thus, naphthalene is the most suitable substitution for introducing fullerene derivatives on the graphene surface via π–π stacking. Additionally, compared to C60 and Sc3N@C80, the C70 fullerene core delivered the greatest results.

The low long-range conductivity of fullerene severely hinders the performance of supercapacitors that use this material. It is therefore anticipated that active carbons based on fullerene will have large capacitances when they are developed. By manipulating fullerene self-assembly with a cobalt tetramethoxy phenylporphyrin (CoTMPP) and pyrolysis, mesoporous carbon composites doped with varying

### *Carbon Nanomaterials Based Supercapacitors: Recent Trends DOI: http://dx.doi.org/10.5772/intechopen.106730*

concentrations of cobalt (Co) and nitrogen (N) were synthesized by Jiang et al. [46]. C60 crystals encapsulated CoTMPP, which underwent carbonization to become actively-bound Co–N in the carbon structures. The ratio of CoTMPP in C60 crystals and the distribution state in superstructures influence the concentration of Co–N. The electrochemical performance of porous carbon composite was greatly improved by Co–N. The fabricated carbon composite demonstrated an improved specific capacitance of 416.31 F g<sup>−</sup><sup>1</sup> at 1 A g<sup>−</sup><sup>1</sup> , which is over ten times greater than that of the pristine C60, and had no activity loss after at least 5000 cycles.

Orderly mesoporous fullerene/carbon hybrids were synthesized by combining the fullerene precursor in chloronaphthalene with varying quantities of sucrose


#### **Table 1.**

*Some latest fabricated carbon-based supercapacitor electrodes.*

and employing mesoporous silica SBA-15 as a template [47]. Different samples MC60@C-X, where X denotes the weight ratio of the fullerene C60 and sucrose were prepared. The ideal EDLC behavior was observed for all samples as deduced from CV curves. By decreasing the C60/sucrose ratio from 2 to 1.33, the calculated specific capacitance increased and then reduced as the ratio fell to 0.8. The highest specific capacitance of 213 F/g at 0.5 A/g was achieved for the MC60@C-1.33 electrode, which is higher than pure mesoporous fullerene prepared without sucrose molecules. Using superior textural parameters, the authors of this study demonstrated that incorporating carbon into the fullerene matrix enhanced the electrical transport and diffusion of the electrolytes. In addition, the research findings suggested that the presence of carbon layers between the fullerenes helped to strengthen the connection between the molecules of fullerene and promoted the electronic transition.

**Table 1** summarizes some features of carbon-based supercapacitor electrodes that have been recently reported.
