Self‐Nitrogen‐Doped Porous Biocarbon from Watermelon Rind: A High‐Performance Supercapacitor Electrode and Its Improved Electrochemical Performance Using Redox Additive Electrolyte

Abstract

Self‐nitrogen‐doped biocarbons are obtained from the watermelon rind via an easy one‐step pyrolysis‐activation process. Porous biocarbon AC W ‐2, obtained with a watermelon/potassium hydroxide (KOH) mass ratio of 1:2 at 700 °C, exhibits a large specific surface area of 1303.3 m 2 g −1 and is decorated with abundant nitrogen/oxygen‐containing functional groups. When AC W ‐2 is used as a supercapacitor electrode, a high specific capacitance of 260 F g −1 is achieved at a current density of 1 A g −1 . AC W ‐2 also exhibits an ultrahigh cycling stability, and its retention rate is maintained at 93.8% even after 5000 cycles at a scan rate of 100 mV s −1 . Furthermore, AC W ‐2 acquires a supramaximal specific capacitance (852 F g −1 ) and a high energy density (12.9 Wh kg −1 ) when p ‐phenylenediamine redox additive is added into the KOH electrolyte. Therefore, the watermelon rind can be used as a promising biomass precursor, and the as‐prepared porous biocarbon is expected to be an outstanding comprehensive electrode material for electrochemical supercapacitors.