Synthesis and Electrochemical Characterisation of Carbon-Based Nanomaterials from Agricultural Biomass for Supercapacitor Applications in Nigeria

Supercapacitors based on high-surface-area carbon nanomaterials from renewable agricultural biomass represent an attractive energy storage technology aligned with Nigeria's agricultural waste valorisation priorities and the need for scalable local material production for portable electronics and grid stabilisation applications. This study synthesises and characterises porous carbon nanomaterials from two agricultural biomass sources abundantly available in Nigeria: sugarcane bagasse from Jigawa State and coconut shells from Delta State. Biomass is carbonised at temperatures between 600 and 1000 degrees Celsius under nitrogen atmosphere and activated by carbon dioxide physical activation and potassium hydroxide chemical activation at varying impregnation ratios and temperatures. Carbon nanomaterial characterisation employs Brunauer-Emmett-Teller analysis, non-local density functional theory pore size distribution modelling, Raman spectroscopy for graphitic order assessment, X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy for surface chemistry analysis. Electrochemical performance is evaluated in a three-electrode cell using one molar sulphuric acid and one molar potassium hydroxide electrolytes by cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. Specific capacitance, energy density, power density, Coulombic efficiency, and cycle stability over 5000 galvanostatic cycles are calculated. The relationship between activation conditions, surface area, pore size distribution, and specific capacitance is systematically analysed. Findings establish structure-property-performance correlations for biomass-derived carbon supercapacitor electrodes, providing locally relevant materials design guidelines for energy storage applications in Nigeria. Keywords: supercapacitor, porous carbon, agricultural biomass, activation, electrochemical performance