Double layer properties of spent coffee grounds-derived carbon activated with potassium hydroxide (koh)

Abstract

Large amounts of spent coffee grounds (SCGs) are generated all over the world. Since SCGs contain a lot of carbon and inherently has a porous structure, SCGs are considered to be a valuable industrial resource by carbonization. According to our previous research, it was apparent that the specific surface area of SCGs-derived carbon was greatly improved by potassium hydroxide (KOH) activation. In this research, we prepared an electric double layer capacitor (EDLC) using SCGs-derived carbon activated with KOH, and compared them to phenol resin-derived activated carbon (MSP-20, Kansai Coke and Chemicals Co., Ltd.), which is commonly used as a reference material in EDLC research. Electrodes were prepared by mixing 80wt% activated carbon, 10wt% carbon black and 10wt% polytetrafluoroethylene (PTFE) and the electrolyte used was 1M triethylmethylammonium-tetrafluoroborate (TEMA-BF4)/propylene carbonate (PC). The capacitive performance was evaluated by a constant current chargedischarge cycle measured with various electrical current loads from 5 to 150mA/cm2. Although the capacitance of SCGs-derived carbon activated with KOH was inferior to that of MSP-20 at low current load density, it had high capacitance in high rate charge-discharge cycles. This suggests that the EDLC consisting of SCGs-derived activated carbon electrodes is superior to MSP-20 in capacitance retention rate when used at a high electric current density. © The Electrochemical Society of Japan, All rights reserved.