Activated carbon derived from corncob via hydrothermal carbonization as a promising electrode for supercapacitors

Activated carbon has been synthesized from corncob via hydrothermal treatment at 200 °C for 7 h with and without activating agents, followed by carbonization at 400 °C for 3 h. The X-ray diffraction patterns show peaks corresponding to the amorphous and graphitic carbon phases. The SEM studies reveal meso and macro pores. The H₃PO₄ treated sample (CC-H-400) shows the highest Brunauer-Emmett-Teller surface area (68.54 m² g^-1). Raman spectra indicate the typical D and G bands. The CC-H-400 shows the highest specific capacitance value of 41 F g^-1 among all the samples. The energy and power density values of the supercapacitor working electrode in a three-electrode setup are 5.7 W h kg^-1 and 500.4 W kg^-1, respectively, for the CC-H-400. Furthermore, the CC-H-400 exhibits excellent stability with a retention rate of 88 % after 2000 charge-discharge cycles at 10 A g^-1 without any shape change, as well as a low equivalence series resistance (ESR) value of 3.96 Ω.