Hydrotrope-assisted interconnected mesoporous polyindole-decorated carbon nanotubes: synthesis, characterisation, and fabrication of asymmetric supercapacitor

Abstract

Recently, polyindole (PIN) has been featured as one of the rising conducting polymers. It has been testified with several composites, including multiwalled carbon nanotubes, via several techniques. These techniques include chemical oxidation, electrospinning, emulsion, and electrochemical or interfacial polymerisation. However, they feature the use of costly and environmentally unfriendly organic solvents to deal with the organic chemistry of indole. Although water has been used as a solvent, it has to be used with a surfactant. The resulting composite with these techniques suffers from low yield, mixed morphology, non-porous and low specific capacitance. For the first time, this work features a facile polymerisation technique of PIN-decorated carbon nanotubes (PC) assisted by hydrotropes in water. The resulting nanocomposite was observed to be interconnected mesoporous and conductive in nature as investigated by several physicochemical and morphological characterisations, viz. FESEM, TEM, RAMAN, and FTIR. In addition to these, the PC was also subjected to electrochemical study through several techniques, including cyclic voltammetry, galvanic charging–discharging, and impedance spectroscopy. The as-synthesised PC showed a maximum specific capacitance of 194.12 F g⁻¹ at the maximum energy density of 62.12 W h kg⁻¹. Finally, to complement the electrochemical performance, an asymmetric supercapacitor device was fabricated using a synthesised PC along with activated carbon and connected in series with an LED. The LED was successfully illuminated indicating the conductive nature of the PC. Furthermore, a digital watch was also connected in a series that stayed on for at least 5 minutes, suggesting the charge storage ability of the PC. Conclusively, this PC that was synthesised using the facile technique with hydrotropes and tetra-n-octyl ammonium bromide (TOAB) can be a promising electrode nanomaterial for several charge storage applications.