PREPARATION OF ACTIVATED CARBONS FROM A FOOD WASTE OF CARBOHYDRATE AND THEIR ELECTROCHEMICAL PERFORMANCE

摘要

Activated carbons were prepared by carbonization and activation from stale rice cake as a food waste of carbohydrate. Commercially available rice cakes made of Japanese glutinous rice were used as starting materials enough after the shelf life. The rice cake and that dried at 60°C for 3 hrs were carbonization at temperatures of 800 and 900°C for 1h in a flow of nitrogen and then activated in air at a temperature of 500°C. The rice cake was also carbonized at temperatures of 700, 800 and 900°C for 30 min and then activated in a flow of CO_2 at 900°C for 10 and 20 min. The structure of the obtained samples was examined by X-ray diffraction. The electrochemical performance was evaluated in 1M-H_2SO_4 aqueous solution using a three-electrode-cell by cyclic voltammetry CV and galvanostatic charge/discharge cycling GC. The nitrogen adsorption measurements were conducted at 77K for a part of the samples. The yields of the activated samples were less than 10wt%. Turbostrtic structure was improved in the carbons obtained from dried rice cake. The values of BET surface area and electric double layer capacitance EDLC for the carbons derived from the pristine rice cake were much larger than that for the carbons derived from the dried rice cake. After the activation, both BET surface area and EDLC values were improved remarkably. The EDLC values for the activated carbons derived from the dried rice cake are smaller than those for the activated carbons derived from the pristine rice cake. For rice cake heat-treated at 800°C for 30 min and then activated at 900°C for 10 and 20 min in CO_2 flow, large values of EDLC were obtained as 160 F/g evaluated from CV and about 200 F/g evaluated from GC. There is a possibility, therefore, that the stale rice cake as a food waste can be applied to an electrode material of the electric double layer capacitor after the appropriate carbonization and activation.