Biowaste-Derived Hierarchical Porous Carbon Nanosheets for Ultrahigh Power Density Supercapacitors

Low-cost activated carbons with high capacitive properties remain desirable for supercapacitor applications. Herein, a three-dimensional scaffolding framework of porous carbon nanosheets (PCNSs) has been produced from a typical biowaste, namely, ground cherry calyces, the specific composition and natural structures of which have contributed to the PCNSs having a very large specific surface area of 1612 m² g⁻¹, a hierarchical pore size distribution, a turbostratic carbon structure with a high degree graphitization, and about 10 % oxygen and nitrogen heteroatoms. A high specific capacitance of 350 F g⁻¹ at 0.1 A g⁻¹ has been achieved in a two-electrode system with 6 m KOH; this value is among the highest specific capacitance of biomass-derived carbon materials. More inspiringly, a high energy density of 22.8 Wh kg⁻¹ at a power density of 198.8 W kg⁻¹ can be obtained with 1 m aqueous solution of Li₂SO₄, and an ultrahigh energy density of 81.4 Wh kg⁻¹ at a power density of 446.3 W kg⁻¹ is realized with 1-ethyl-3-methylimidazolium tetrafluoroborate electrolyte.