From hard carbon to activated carbon: influence of surface area and pore structure on the electrochemical performance of coconut rachis-derived supercapacitor electrodes

The performance of supercapacitors depends on the structural characteristics of electrode materials and their interactions with electrolytes. In the present work, hard carbon (HC) and chemically treated coconut rachis-derived activated carbon (AC) are comparatively studied to understand the role of porosity and surface area on electrochemical performance. Through chemical activation, the compact structure of HC was converted to a well-developed porous AC, resulting in an increased specific surface area from 32 to ~ 1025 m 2 g −1 . Such AC provided rich electrochemically active sites along with efficient transport of electrolyte ions. Structural and compositional changes induced by activation were characterised using FESEM, BET, EDX, XRD, FTIR, and Raman spectroscopy. Electrochemical performances of HC and AC were analysed using different aqueous electrolytes. In all electrolytes, AC showed better capacitive behaviour than HC due to the well-developed porous system and high surface area. AC in 6 M KOH showed a maximum specific capacitance of 201 F g −1 . The symmetric supercapacitor assembled using AC in 6 M KOH exhibited a cell-level specific capacitance of 35 4 F g −1 and retained ~ 93% of its initial capacitance after 2000 charge–discharge cycles. These findings demonstrate that engineering the pore structure and surface area of biomass-derived carbon is essential for enhancing supercapacitor performance.