Soybean Root-Derived Hierarchical Porous Carbon as Electrode Material for High-Performance Supercapacitors in Ionic Liquids

Soybeans are extensively cultivated worldwide as human food. However, large quantities of soybean roots (SRs), which possess an abundant three-dimensional (3D) structure, remain unused and produce enormous pressure on the environment. Here, 3D hierarchical porous carbon was prepared by the facile carbonization of SRs followed by chemical activation. The as-prepared material, possessing large specific surface area (2143 m2 g–1), good electrical conductivity, and unique 3D hierarchical porosity, shows outstanding electrochemical performance as an electrode material for supercapacitors, such as a high capacitance (276 F g–1 at 0.5 A g–1), superior cycle stability (98% capacitance retention after 10,000 cycles at 5 A g–1), and good rate capability in a symmetric two-electrode supercapacitor in 6 M KOH. Furthermore, the maximum energy density of as-assembled symmetric supercapacitor can reach 100.5 Wh kg–1 in neat EMIM BF4. Moreover, a value of 40.7 Wh kg–1 is maintained at ultrahigh power density (63000 W kg–1). These results show that the as-assembled supercapacitor can simultaneously deliver superior energy and power density.