Activated carbon from citric acid catalyzed hydrothermal carbonization and chemical activation of salacca peel as potential electrode for lithium ion capacitor’s cathode

Abstract

Activated carbon (AC) has been utilized for various applications including as an electrode for supercapacitor, i.e., electric double-layer capacitor (EDLC) as well as hybrid capacitor such as lithium ion capacitor. In this research, salacca peel was used as a raw material for AC. It was chosen among other biomass wastes because it is abundant and is still considered as a waste. The hydrothermal carbonization was conducted at 5 MPa, temperature of 200–250 °C, and 5 h in subcritical water, which is a green dehydrating agent. The effect of parameters (temperature and addition of citric acid as a catalyst) on the hydrochar and AC product was investigated. The hydrochar from hydrothermal carbonization was activated by chemical activation using potassium hydroxide (KOH) as an activated agent to enhance the surface area and porosity. The morphology of both hydrochar and AC was measured by scanning electron microscopy (SEM), its chemical transformation was measured by Fourier transform infrared spectroscopy (FTIR) while the surface area and pore size distribution were measured by nitrogen adsorption at 77.35 K. The electrochemical performance of activated carbon from salacca peel as well as commercial activated carbon using a coin cell in a Li half-cell system was evaluated by CV, GCD, and EIS. The results show that the presence of citric acid contributes to higher specific capacitance in the rate performance test of LIC at different current density as well as in long rate stability test.