Coal-Based Nanoporous Carbon Electrode for High-Performance Supercapacitor: Surface and Diffusion Charge Kinetics in Aqueous and Non-Aqueous Electrolytes

Abstract

South Africa generates around 60 million tonnes of coal discards each year, with over 1.2 billion tonnes landfilled in discard dumps and slurry ponds. The huge quantity of coal discards generated within the past decades, which is a significant liability to the mining industry and the environment, presents an opportunity to reuse this resource. This study investigated the potential of nanoporous carbon material from coal discard via KOH activation for use as electrode material in supercapacitors. Hierarchical morphology is seen via scanning electron microscopy (SEM). Raman spectroscopy reveals structural defects, X-ray Diffraction spectroscopy (XRD) confirms the material's amorphous nature, and N2 at 77k adsorption reveals a carbon material with high porosity and a surface area of 1424 m2/g.Electrochemical analysis reveals that the charge storage mechanism of the material is surface-controlled (non-faradaic) in the non-aqueous (TEABF4/ACN) electrolyte and diffusion-controlled (faradaic) mechanism in the aqueous (Na2SO4) electrolyte. The material has a higher specific capacitance (162 F/g) and cycling stability of 87.1% capacitance retention after 5000 cycles in Na2SO4. The material exhibits a better rate capability in TEABF4/ACN with 92.3% capacitance retention. A symmetrical two-electrode device using Swagelok T-cell assembly achieves energy densities of 15.5 and 10.4 Wh/kg in Na2SO4 and TEABF4/ACN, respectively, and a power density of 100 W/kg in both electrolytes. The variation in the capacitive performance of the material in both electrolytes is due to differences in electrolyte ion size, ionic conductivity, and pore structure. This study not only establishes a link between the structure of coal-based nanoporous carbon and its electrochemical performance in both electrolytes but also demonstrates the potential of coal-based functional materials for sustainable energy storage.