Activated Coconut Shell Charcoal Flakes as Supercapacitor Electrodes: Electrochemical Performance and Structural Characterization

Abstract

This study investigates the potential of utilizing coconut shell charcoal flakes as a sustainable precursor for Activated Carbon (AC) electrodes in supercapacitors. Five activation cycles labeled AC1 to AC5 were electrochemically and structurally analyzed using Raman spectroscopy, scanning electron microscopy, cyclic voltammetry, galvanostatic charge-discharge, electrochemical impedance spectroscopy, and long-term cycle stability testing methods. Raman spectra revealed distinct D and G bands near 1,345 cm^-1 and 1,590 cm^-1. Among the samples, AC3 showed the most favorable structure, with an I_D/I_G ratio of 0.872, indicating a balanced degree of disorder and graphitic character that supported better electrochemical behavior. Microstructure analysis confirmed that AC3 possessed a well-developed, interconnected micropore-mesopore network, while over-activation in AC4 and AC5 led to pore merging and structural breakdown. Electrochemical results demonstrated that AC3 achieved the highest specific capacitance and energy density, reaching about 3.123 F g^-1 and 0.434 W h kg^-1 at a 10 mV s^-1 scan rate. Impedance data showed that AC3 allowed effective ion transport and maintained a mainly capacitive response, with a moderate charge transfer resistance of around 6 Ω. In contrast, the over-activated samples exhibited reduced ion mobility. Long-term cycling tests confirmed that AC3 retained most of its capacitance after 1,000 charge-discharge cycles, indicating strong durability. Overall, coconut shell-based activated carbon, particularly at the AC3 activation stage, presents a cost-effective and eco-friendly electrode material with strong potential for advanced, sustainable supercapacitor applications.