A comparative study on porous activated carbon derived from waste biomass with varying oxygen functionalities as supercapacitor electrodes

Abstract

Activated carbon derived from biomasses with different oxygen‐bearing chemical constituents has been explored as supercapacitor electrode. The rice straw (RS) and eucalyptus wood biomasses were selected owing to their contrasting composition of cellulose, hemicellulose, and lignin contents. The activated carbons of these biomasses are obtained by pyrolysis at 550°C followed by thermal activation (700°C) after treatment with optimized KOH. The specific capacitance of RS‐based activated carbon (ACRS‐700), measured from galvanostatic charging‐discharging studies at 0.5 A g⁻¹, is much higher (eg, 365 F g⁻¹) than that of ACEW‐700 (168 F g⁻¹). The higher specific capacitance of ACRS‐700 is attributable to: (i) significantly higher surface area (3345 m² g⁻¹) comprising of interconnected micro‐ and mesoporous structure; (ii) porosity of about 2.0 cm³/g; and (iii) oxygen‐rich hemicellulose contents. The possible charge storage mechanism in ACRS‐700 has been discussed. The real‐time application of ACRS‐700 has been demonstrated by lighting up red LEDs using ACRS‐700//ACRS‐700 symmetric supercapacitor device, operated with aqueous and freshly synthesized [Bu₄N⁺][NO₃⁻] ionic liquid as electrolytes. The maximum energy density (42.7 Wh kg⁻¹) and the power density (1.9 kW kg⁻¹) for ionic liquid electrolyte are favourable for supercapacitor applications.