High-efficiency one-step microwave method for high-performance biomass-based hierarchical porous carbon

Biomass shows intrinsic superiorities to produce hierarchical porous activated carbon with microwave heating. However, biomass is incapable of absorbing microwave energy, and additional microwave absorbers must be added. Herein, a crucible capable of absorbing microwave waves was employed to simplify the process to produce a hierarchical corncob-based porous carbon (HCCPC) using a microwave-assisted one-step physical-chemical coupled activation method without additional microwave absorber being added. The resulting HCCPC possessed a high specific surface area of 1948 m(2)/g, a high mesopore ratio of 35.5%, and a high graphitization degree of I-G/I-D= 1.55. The corresponding capacitive performances of HCCPC-based symmetrical two-electrode supercapacitors (SCs) were investigated in aqueous, organic, and ionic liquid electrolytes. The SC with KOH electrolyte showed the highest specific capacity of 281 F/g at 0.5 A/g and the most outstanding cyclic durability of 100% at 0.5 A/g after 10,000 cycles. Meanwhile, the SC with 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) ionic liquid electrolyte could obtain the highest energy density of 48.2 Wh/kg at a power density of 900 W/ kg. These results demonstrate that employing a crucible capable of absorbing microwave energy in the microwave-assisted one-step physical-chemical coupled activation is universal and feasible to prepare biomass-based hierarchical porous carbon for high-performance SCs.