Lignin derived activated carbon particulates as an electric supercapacitor: carbonization and activation on porous structures and microstructures†
Microporous and mesoporous particulate activated carbons (PACs) with unique hierarchical microstructures were facilely synthesized from alkali lignin via simultaneous carbonization and alkali hydroxide activation. Both NaOH and KOH activated PACs contained slit-like micropores and carbon microstructures with circular nanoplates of graphite-like basal planes and amorphous carbon clusters. The micropores broadened with increasing temperatures, holding time and alkaline hydroxides. The basal planes sizes and order were enhanced with increasing temperatures and holding time but lowering impregnation ratios, while amorphous carbon showed no particular patterns due to its much higher reactivity toward alkali hydroxides. The PACs with the highest micropore surface area and pore volume (1100 m2 g−1, 0.43 cm3 g−1) were obtained at 900 °C, 30 min and an impregnation ratio of 1 and fabricated into electrical supercapacitors to exhibit excellent 226 F g−1 specific capacitance, 7.8 W h kg−1 energy density and 47 kW kg−1 power density as well as over 92% capacitance retention after 5000 cycles.