Biomass derived activated carbon-based high-performance electrodes for supercapacitor applications

Biomass-derived activated carbon has been prepared from a bio-source (peanut shells) and investigated as an electrode material for supercapacitors. The biomass-derived carbon was prepared by the hydrothermal method and activated using KOH. The material was characterized using a transmission electron microscope, scanning electron microscope, X-ray diffraction and Fourier transform infrared spectroscopy respectively. The surface area of the prepared material was analysed using Brunauer–Emmett–Teller technique. Electrochemical studies were carried out in both three and two-electrode configurations. From cyclic voltammetric studies, the electrical double layer capacitance behavior of the electrode was analysed. The specific capacitance estimated from galvanostatic charge–discharge (GCD) studies was 247 F/g at a current density of 0.25 A/g. Kinetic studies revealed more of a capacitive contribution to the diffusion component. A symmetric supercapacitor was fabricated in a Swagelok cell and the device characteristics were analysed. The cell voltage was found to be 0–1 V and the specific capacitance estimated from GCD was found to be 98 F/g at a current density of 0.25 A/g. Finally, cyclic stability studies were carried out for 5000 and 20,000 cycles and remarkable capacitance retention of 90% and 97%was obtained in the three and two-electrode configurations respectively. In addition voltage holding test was performed in the voltage range of 0.8 to 1.2 V to ascertain the stability of the supercapacitor. The changes at the electrode–electrolyte interface were analysed by electrochemical impedance spectroscopy.