Low-cost supercapacitor based on multi-walled carbon nanotubes and activated carbon derived from Moringa Oleifera...

An electric double-layer capacitor (EDLC) was fabricated using multi-walled carbon nanotubes (MWCNT) and activated carbon (AC) derived from Moringa Oleifera fruit shells as electrode material. The carbonization temperature and the weight ratio of the fruit shells to the activating agent were varied to determine the best condition in the fabrication of the electrodes. Activation of the carbonized fruit shells by ZnCl₂ resulted in the formation of pores as verified by the scanning electron micrographs. Energy dispersive X-ray analyses show that the washing of the carbonized sample resulted in the removal of zinc and chlorine residues. The supercapacitor electrodes were fabricated by adding polyvinylidene fluoride and N-methylpyrrolidone to the MWCNT-AC mixture to form a slurry and was cast onto a nickel foam. The capacitance of the fabricated electrodes was determined using a potentiostat. The activated carbon with a carbonization temperature of 800 °C and a 1:2 weight ratio between the fruit shells and ZnCl₂ was observed to have the highest capacitance of 130 F g^-1 and was duplicated to fabricate the supercapacitor electrodes. A glass microfiber filter was soaked in 3 M KOH and placed in between the two electrodes. The specific capacitance of the EDLC was found to be 122 F g^-1 at a current density of 0.5 A g^-1, average energy density of 17 W h kg^-1, average power density of 1.5 kW kg^-1 and an equivalent series resistance of 1.6 Ω. After 100 scans with a scan rate of 0.1 V s^-1, the percent decrease in capacitance was calculated to be 2.65 % of its original capacitance.