Ultrahigh‐Surface Area Hierarchically Porous Carbon Derived From Sweet Potato Extraction Residue‐Syrup for High Performance Supercapacitor

Converting biomass waste into value-added products is desirable and a major goal for the circular economy. Herein, the agricultural waste and sweet potato extraction residues (SPR) were converted into hierarchially porous carbons (HPCs) by a facile method using KOH as the activation agent. The as-obtained SPR-HPCs exhibited a well developed pore structure and very high specific surface area (SSA). By controlling the fabrication conditions including the dosage of KOH and activation temperature, the optimized SPR-HPC-3.5-800 had an ultrahigh SSA of 3206 m² g^-1 with high pore volume of 2.132 cm³ g^-1. When used as electrode materials, the electrochemical studies demonstrated that the SPR-HPC-3.5-800 based electrode achieved high specific capacitance of 320 F g^-1 at a current density of 0.5 A g^-1 and the symmetrical supercapacitor in 6 M KOH achieved energy density of 6.8 Wh kg^-1 at 249 W kg^-1. Furthermore, high electrochemical stability was achieved for the SPR-HPCs. This study provides a good example of the production of value-added products from biowastes.