Abstract
Converting agricultural lignocellulosic biomass into high-performance porous carbon electrodes provides a sustainable route for electrochemical energy storage. However, establishing rigorous mechanistic correlations between chemical activation stoichiometry, sub-nanometer pore evolution, and electrolyte transport kinetics at high charge–discharge rates remains a persistent challenge. Herein, we systematically investigate the impact of potassium hydroxide ("KOH" ) activation severity across varying mass ratios ("KOH":"char" of 0:1, 1:1, 3:1, and 4:1) on carbon derived from coconut shell (Cocos nucifera) waste. Non-Local Density Functional Theory ("NLDFT" ) deconvolution of 77" K " "N" _2 adsorption isotherms reveals that moderate etching ("KOH":"char"=3:1) optimizes the development of slit-shaped micropores (<2" nm" ), yielding an apparent Brunauer–Emmett–Teller ("BET" ) surface area of 2160〖" m" 〗^2 〖" g" 〗^(-1) and a micropore volume of 0.84〖" cm" 〗^3 〖" g" 〗^(-1). In contrast, severe activation (4:1) induces localized pore-wall collapse, broadening the sub-nanometer networks into mesoporous channels (2"--" 5" nm" ) while lowering the apparent surface area to 1890〖" m" 〗^2 〖" g" 〗^(-1) and overall carbon mass yield to 9.2%. When evaluated in 6" M KOH" electrolyte, the 3:1 activated sample delivers a maximum single-electrode gravimetric capacitance of 314.8" F" 〖" g" 〗^(-1) at 0.5" A" 〖" g" 〗^(-1) in a three-electrode configuration and 248.6" F" 〖" g" 〗^(-1) in a symmetric two-electrode coin-cell device. Notably, the mesopore-broadened 4:1 architecture exhibits superior rate resilience, retaining 83.1% of its initial capacitance at 10" A" 〖" g" 〗^(-1) compared to 76.5% for the 3:1 material. Electrochemical impedance spectroscopy confirms that the expanded mesoporous network mitigates interior diffusion resistance, yielding an equivalent series resistance of 0.46" " Ω and a short relaxation time constant of 0.78" s" . Furthermore, symmetric coin cells retain 97.8% of initial capacitance over 10,000 continuous galvanostatic cycles at 5" A" 〖" g" 〗^(-1). This work elucidates the structural trade-off between energy storage density, high-current rate capability, and synthetic yield in biomass-derived carbon electrodes.