Hierarchical porous carbon with high nitrogen content derived from plant waste (pomelo peel) for supercapacitor

The plant waste pomelo peels are used as carbon precursors to fabricate nitrogen-doped hierarchical porous carbon. The sample PC600 is fabricated at mild calcination temperature of 600 °C, which has nitrogen content of as high as 4.47% and hierarchical pores with a BET surface area of 1104 m2 g−1. The symmetric supercapacitor based on PC600//PC600 electrodes exhibits excellent electrochemical performance benefiting from both the electric double-layer capacitance and pseudocapacitance of PC600. In 1 M H2SO4 electrolyte, this supercapacitor delivers gravimetric capacitance of 208.7 F g−1, volumetric capacitance of 219.3 F cm−3, and energy density of 7.3 Wh kg−1 at a current density of 1 A g−1. Furthermore, the extraordinary energy density of 21.6 Wh kg−1 at 1 A g−1 and 17.1 Wh kg−1 at 20 A g−1 are obtained in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) electrolyte. The suitable calcination process can make the contents of nitrogen atoms and pores structures in PC600 to achieve an optimal combination, leading to improved electrochemical performance.