Bamboo-derived activated carbon prepared by superheated steam (BAC) exhibited performance for utilization as an electric double layer capacitor (EDLC) electrode. Pore structure and EDLC performances were investigated by comparison with phenol resin-derived activated carbon (MSP-20), which is commercially available and often used for the purpose. The nitrogen adsorption isotherm showed that BAC had a large BET-specific surface area of 1268 g/m 2 with a developed pore structure, especially of the mesopore, in comparison with MSP-20. It is considered that inherent ash in bamboo promoted activation, in addition to physical activation by superheated steam. Capacitance per electrode volume (C V) was 52 F/cm 3 with BAC. Because the density of BAC is high (0.78 g/cm 3) compared with that of MSP-20 (0.58 g/cm 3), sufficient C V for usage was obtained, although the capacitance per electrode mass (C M) at 5 mA/cm 2 itself of BAC (67 F/g) was lower than that of MSP-20 (126 F/g). With IR drop, the resistance value of BAC (9.7 Ω) was lower than that of MSP-20 (10.5 Ω). Especially, the diffusion resistance of BAC disclosed to be smaller than that of MSP-20. These results indicated that BAC produced by steam activation is a promising material with a pore structure suitable for ion transfer in EDLC.

To improve the specific surface area (SSA) of steam activated carbon that has been prepared from spent coffee grounds (SCG), a demineralization of the SCG was conducted. As the ash content of the SCG decreased, fine micropores developed during the activation, leading to a significant increase in the SSA. An electric double layer capacitor was assembled and then evaluated, with the evaluation results indicating that the capacitance per electrode weight, the capacitance retention in relation to the current density, and the internal resistance were superior for activated carbon with a higher SSA.However, the capacitance per electrode volume had a maximum value under certain conditions, which were considered well balanced in terms of the SSA and electrode density.