Hierarchically Porous N‐Doped Carbon Nanosheets Derived From Grapefruit Peels for High‐Performance Supercapacitors

In this work, the low-cost hierarchically porous nitrogen-doped carbon nanosheets (PNCNs) were prepared via one-step carbonization and KOH activation process of grapefruit peels. The prepared PNCNs exhibit higher specific surface area due to the inducement of the KOH-assisted carbonization compared to directly carbonized grapefruit peels (DCGPs). The PNCNs exhibit excellent electrochemical performances with high specific capacitance up to 311 F g−1, superior cycling stability over 10000 cycles with only 5.95 % capacitance degradation, high energy density of 17.7 W h kg−1 and power density of 1100 W kg−1 in 1 mol L−1 H2SO4 electrolyte. All these electrochemical data are significantly better than the comparative DCGPs material. Moreover, the assembled symmetric supercapacitor in 1 mol L−1 Na2SO4 aqueous electrolyte exhibits a high energy density of 34.05 W h kg−1 at a power density of 180 W kg−1 and retains 14.25 W h kg−1 even at 5400 W kg−1.