Template-free preparation of mesoporous carbon from rice husks for use in supercapacitors

Mesoporous carbon (MC) was prepared from rice husk (RH) by a simple and template-free method which combines H₃PO₄ activation with a pretreatment of the RH with a NaOH solution and pre-oxidation in air. The pretreatment of RH with NaOH removes silicon and damages the crystal structure of the cellulose in the RH, both of which are beneficial to the preparation of MC with a high surface area and high mesoporosity. The MC has a specific surface area of 2 009 m²·g^-1 and a mesoporosity of 90.8%. Its specific capacitance can reach 176 F·g^-1 at a current density of 50 mA·g^-1, and a value of 126 F·g^-1 is retained at 1 000 mA·g^-1, indicating an excellent rate capability. A MC electrode has a stable specific capacitance of about 150 F/g at 200 mA·g^-1 with no apparent capacitance fade after 1 000 cycles, indicating good electrochemical stability.