Sponge-like nanoporous activated carbon from corn husk as a sustainable and highly stable supercapacitor electrode for energy storage

Corn husk, an abundant agro-industrial waste was employed to produce activated carbon for energy storage. The sponge-like activated carbons were produced with environmentally friendly potassium carbonate (K2CO3) at different impregnation ratio (corn husk: K2CO3; 1:1 to 1:3) and activation temperatures (500–800 °C). The obtained activated carbon was used to produce electrodes for supercapacitor application. The results revealed that corn husk: K2CO3 ratio of 1:2 and 650 °C promoted mainly nanopores (0.773 nm) with appreciably higher specific surface area (1115 m2/g) and a sponge morphology. The electrochemistry performance test on the materials shows specific capacitances of up to 269 F/g at 5 mV/s scan rate for a material obtained at 650 °C. The textural characteristics, morphology and heteroatoms of sulfur and nitrogen significantly promoted higher energy storage capacity. This activated carbon was employed to assemble a symmetric supercapacitor in acidic electrolyte (0.5 M H2SO4) that delivered up to ~10 Wh/kg and was very stable, maintaining about 99.5 % of its original energy after 20,000 charge/discharge cycles.