Microporous activated carbons from coconut shells produced by self-activation using the pyrolysis gases produced from them, that have an excellent electric double layer performance

Abstract

Coconut shell-based activated carbons were prepared by self-activation using the pyrolysis gases generated from them. The process was carried out at high temperatures in a closed reactor filled with coconut shell under a high pressure that was generated by pyrolysis gases. Results indicate that the activated carbon prepared at 900 °C for 6h has a specific surface area, total pore volume, micropore percentage, iodine adsorption capacity and methylene blue adsorption capacity of 1 194.4 m2/g, 0.528 cm3/g, 87.8%, 1 280 mg/g and 315 mg/g, respectively. When used as the electrode material of electrochemical capacitors this activated carbon exhibits a specific capacitance of 258 F/g, a high capacitance retention rate of 97.2% after 3000 charge/discharge cycles and a small impedance. The water vapor and carbon dioxide generated by the pyrolysis of the coconut shell in the closed reactor act as activating agents and also increase the pressure of the reaction system. This is favorable for the activation of the formed char. This self-activation method was also used to prepare activated carbons with high adsorption capacities for iodine and methylene blue from almond stones, pecan shells and slash pine sawdust, indicating that it is a very simple, efficient, environmentally friendly and economical method for the preparation of biomass-based activated carbons for supercapacitor electrode materials and adsorption.