Biomass-derived carbon from coconut shell and kluwak shell for electrical double-layer capacitor applications

Biomass-derived carbon materials have attracted considerable attention as sustainable and low-cost electrode materials for electrical double-layer capacitors (EDLCs). This study investigated coconut shell and kluwak shell wastes as the precursors for activated carbon (AC) and partially reduced graphene oxide (p-rGO) electrodes. AC derived from both biomasses was oxidized to graphite oxide (GO) using a modified Hummer’s method, followed by microwave-assisted solvothermal reduction in ethylene glycol to produce p-rGO. The novelty has lied in utilizing kluwak shell as an alternative carbon precursor and systematically comparing its electrochemical performance with coconut shell-derived materials under controlled microwave conditions. For coconut shell-derived p-rGO, microwave power was varied at 100, 180, and 300 W, whereas irradiation times of 15, 30, and 45 min had applied to kluwak shell-derived p-rGO. Structural characterization has shown the reduced interlayer spacing and enhanced pore development with increasing microwave intensity, indicating an improved reduction and structural ordering. The electrochemical characterization by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS) demonstrated superior performance of coconut shell-derived materials. The highest specific capacitances of coconut shell AC and p-rGO reached 130.83 and 103.58 F g −1 , respectively, with electrical conductivities of 0.78 and 0.30 S m −1 at 300 W. In comparison, kluwak shell-derived AC and p-rGO exhibited specific capacitances of 1.39 and 3.73 F g −1 and conductivities of 0.063 and 0.157 S m −1 , respectively, after 45 min irradiation. The results have demonstrated a strong correlation between electrical conductivity and electrochemical performance. Overall, coconut shell was a more favorable precursor, while kluwak shell remained as a promising sustainable alternative for biomass-derived carbon electrodes.