Pore Structures and Electric Double Layer Properties of Activated Carbon Derived from Demineralized Spent Coffee Grounds

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.