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 m 2  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 Li 2 SO 4 , 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.