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ENHANCED STORAGE CAPACITY IN SUPERCAPACITORS USING SINGLE WALLED CARBON NANOTUBES

Supercapacitors, also called ultra-capacitors or electrical double-layer capacitors are considered a promising candidate for future energy applications. This is attributed to their outstanding characteristics such as high power density, stability and fast recharge capability with capacitance values much higher than conventional capacitors[1]. Supercapacitors bridge the gap between electrolytic capacitors and rechargeable batteries[1] yet, they face the challenge of achieving the energy-storage capability of batteries without sacrificing their power density and cycling stability [1]. However, they are said to have a long shelf life as compared to batteries. Compared to regular electrolyte capacitors, supercapacitors offer shorter charge and discharge durations.

Single-walled carbon nanotube (SWCNT) based electrodes offer extraordinary energy density storage and an equivalent amount of delivered power compared to the traditional electrodes. This is due to the high surface area, high conductivity and controllable porosity of the SWCNT. The functionalization of material with redox materials has showcased enhanced energy density[2].

Andrew I. Minett et. al. studied the PEDOT/PSS-SWCNT composite films displaying a high specific capacitance of 104 Fg-1 with maximum energy and power density of 7 Whkg-1 and 825 Wkg-1 respectively. This has been attributed to the small diameter of SWCNT in electrodes which causes electrolytes to diffuse easily achieving a higher maximum usable power[3].

HiPCO® SWCNT/PAN composite films have showcased a much higher power density. The efficient utilization of large specific surface area offers enhanced adsorption of electrolyte ions onto the nanotube surface. This effect leads to high energy storage during charging and high power density while discharging.[4].

Cary L. Pint et. al. demonstrated HiPCO® SWCNT foam as binder-free electrode material in supercapacitors and have obtained high cyclic stability and storage capacity. The pristine SWCNT was dispersed in NMP (n-methylpyrrolidone) to form a surfactant-free SWCNT-NMP suspension. SWCNT from the suspension self-assembled on the Ni electrode due to Van der Waal’s forces, enabling careful tuning of the microstructure during the assembly. Comparatively, the microstructure of  SWCNT materials in the CVD process is dictated during the SWCNT growth[5].

The surfactant-free HiPCO® SWCNT self-assembled electrodes showcased good non-Faradaic storage character. The stability is said to be attained by low electrode resistance which is due to the absence of surfactants [5].

Thus, HiPCO® nanotubes are playing a significant role in the enhancement of key properties of energy devices such as supercapacitors.

References:

[1]       W. Lu and L. Dai, “Carbon Nanotube Supercapacitors,” Carbon Nanotub., Mar. 2010.

[2]       S. Arepalli et al., “Carbon-nanotube-based electrochemical double-layer capacitor technologies for spaceflight applications,” JOM, vol. 57, pp. 26–31, 2005.

[3]       D. Antiohos et al., “Compositional effects of PEDOT-PSS/single walled carbon nanotube films on supercapacitor device performance,” J. Mater. Chem., vol. 21, no. 40, pp. 15987–15994, Oct. 2011.

[4]       T. Liu, T. V. Sreekumar, S. Kumar, R. H. Hauge, and R. Smalley, “WNT / PAN composite film-based supercapacitors,” 2003.

[5]       “Solution Assembled Single-Walled Carbon Nanotube Foams: Superior Performance in Supercapacitors, Lithium-Ion, and Lithium–Air Batteries | The Journal of Physical Chemistry C.” [Online]. Available: https://pubs.acs.org/doi/abs/10.1021/jp5054502. [Accessed: 29-Oct-2019].

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