Electrochemical energy storage from spent coffee grounds-derived carbon by KOH activation

Abstract

Carbon obtained from spent coffee grounds (SCG) was activated using various molarities of KOH. Before the chemical activation step, the SCG was carbonized using either an oxidative calcination process at 300 °C in room condition or thermal annealing at 600 °C in an argon atmosphere. We observe that the use of oxidative calcination has a significant effect on the specific surface area of the activated carbon, on the texture, the morphology, and the electrochemical properties. The samples that received oxidative calcination before the chemical activation step showed specific capacitances of around 205 F g−1 at 5 mV s−1, while those carbonized in an argon atmosphere showed specific capacitances of around 82 F g−1 to 5 mV s−1. These differences in electrochemical properties are related to the increase of carboxyl groups on the sample's surface due to the oxidative calcination process. These carboxyl groups interact with K+ ions coming from the KOH solution. The improved impregnation of K+ ions on the SCG that was calcinated in room conditions allows for generating a higher specific surface area (1789 m2 g−1) in these samples compared to those that were thermally annealed in argon (658 m2 g−1).