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 H 2 SO 4 electrolyte. All these electrochemical data are significantly better than the comparative DCGPs material. Moreover, the assembled symmetric supercapacitor in 1 mol L −1 Na 2 SO 4 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 .