Hierarchically Porous Carbon as a High‐Rate and Long‐Life Electrode Material for High‐Performance Supercapacitors

In this study, cost‐effective hierarchically porous carbon (HPC) derived from starch was successfully prepared through a simple mixing and subsequent one‐step carbonization method. Based on the three‐dimensional interconnected hierarchically porous structure, HPC exhibits a high specific surface area of 2259.54 m 2  g −1 and a specific capacitance of 385.7 F g −1 at 1 A g −1 in a three‐electrode system. When the as‐prepared carbon was employed to fabricate an aqueous symmetrical supercapacitor, the device displayed a high specific capacitance of 81.3 F g −1 at 1 A g −1 , and even at 20 A g −1 the specific capacitance remained 64 F g −1 (capacity retention rate of 78.72 % compares with that at 1 A g −1 ), demonstrating an outstanding rate performance. This supercapacitor maintained a capacity retention of 100 % after 60 000 cycles at a current density of 5 A g −1 , indicating superior long‐term cycling stability. Furthermore, when the as‐prepared carbon was employed to fabricate a symmetrical supercapacitor in ionic liquid (1‐ethyl‐3‐methylimidazolium tetrafluoroborate, EMIMBF 4 ) electrolyte, it ultimately achieved an ultrahigh energy density of 133.94 Wh kg −1 (power density of 1997.51 W kg −1 ) and a capacity retention rate of 83.3 % was maintained after 5000 cycles throughout a wide operating potential window of 0–4 V at 10 A g −1 .