Abstract

Biocarbon and activated biocarbon samples were prepared based on rubberwood sawdust biomass. KOH, NaOH, and ZnCl<inf>2</inf> were used as activating agents, while distilled water and sulfuric acid, phosphoric acid, and thiourea solutions were used as reaction media during hydrothermal carbonization. The biocarbon hydrothermally carbonized in sulfuric acid solution, without activation, had the largest specific surface area (621 m² g⁻¹). Hydrothermal carbonization in the phosphoric and the sulfuric acid solutions was more effective than in the thiourea solution and the distilled water in terms of specific surface area. Activation with ZnCl<inf>2</inf> and NaOH led to the dominance of mesopore characteristics, while that with KOH yielded an activated biocarbon with a balance between microporosity and mesoporosity. The cyclic voltammogram curves for the biocarbon/activated biocarbon showed EDLC behavior with some pseudo-capacitance. The activated biocarbon hydrothermally carbonized in phosphoric acid solution and activated with KOH (P-ACK) had the largest specific surface area of 2680 m² g⁻¹ with a pore volume of 1.42 cm³ g⁻¹, a specific capacitance of 482.1 F g⁻¹ at 0.5 A g⁻¹, and outstanding capacitance retention of 103.1 % of its original value at 20,000 testing cycles.