Activated Carbon Utilization from Corn Derivatives for High-Energy-Density Flexible Supercapacitors

Porous activated carbons from four types of corn derivatives (husk, fiber, grain, and cob) are compared for the first time regarding their structural, morphological, and electrochemical characteristics for application as electrode materials in flexible supercapacitors. Benefiting from its hierarchical porous structure, appropriate amount of N and O functional groups, large specific surface area (1804 m² g^-1), and high degree of graphitization, the activated carbon from corn grains displayed the best electrochemical performance as an electrode material for supercapacitor applications; when tested in a three-electrode configuration, it had a high specific capacitance (411 F g^-1 at 1.0 A g^-1) and an excellent rate capacity (85.7% capacitance retention at 30 A g^-1) in an aqueous 6 M KOH electrolyte. The high specific surface area and high degree of graphitization of the activated carbon from corn grains (AC grain) played crucial roles in its excellent energy storage performance. Most importantly, the flexible supercapacitor that was assembled with slot-die coated AC grain electrodes and a hydroxyethyl cellulose (HEC)/KOH biopolymer electrolyte delivered an outstanding electrochemical performance with an energy density of 31.1 Wh kg^-1 at 215 W kg^-1 and ultrahigh cyclic stability (91.3% capacitance retention after 10 000 cycles at a current density of 5 A g^-1). Also, the assembled flexible supercapacitor maintained an energy density of 20.03 Wh kg^-1 even under a high power density of 28.01 kW kg^-1. These findings conclude that the porous carbon material obtained from corn grains has enormous potential as a high-performance electrode material for supercapacitors.