Activated Bio-Carbon from Paper Mill Sludge as Electrode Material for Supercapacitors: Comparative Performance Evaluation in Two Aqueous Electrolytes

This study presents a valorisation approach that converts waste sludge from a South African paper mill into activated biocarbon for energy storage applications. The two-step synthesis using hydrothermal carbonization and NaOH activation of paper mill waste at 700 °C yielded activated biocarbon. N 2 at 77k adsorption showed high porosity carbon material with a surface area of 1139 m2/g. The three-electrode cell in 3M KOH and 1M Na2SO4 electrolyte shows the activated biocarbon electrode exhibits good specific capacitance (Csp) of 233 and 244.2 F/g, respectively. The concentration of the electrolyte reportedly has a significant effect on specific capacitance. In both electrolytes, symmetric triangular curves in galvanostatic charge-discharge indicate a quick charge-discharge process. The two-electrode cell in 3M KOH and 1M Na2SO4 electrolytes delivered specific capacitances of 119 and 152 F/g, respectively, and energy densities of 16.5 and 21.1 Wh/kg. The material had a capacity retention efficiency of 83 and 92% after 5000 cycles in 3M KOH and 1M Na2SO4 electrolytes, respectively. The performance of the activated biocarbon from paper sludge as electrode material clearly shows its potential for electrochemical energy storage. Thus, demonstrating the potential contribution of the pulp and paper industry towards the transition to green energy.