High-performance nitrogen-doped hierarchical porous carbon derived from cauliflower for advanced supercapacitors

Nitrogen-doped hierarchical porous carbon is successfully synthesized from cauliflower with unique structure by a simple pyrolysis process, including a pre-carbonization step of cauliflower and a KOH-activated step of carbonization product. According to this pyrolysis strategy, the pre-carbonization product at 450 °C basically keeps the original structure of cauliflower, beneficial to the deep and uniform activation at 700 °C and the formation of 3D interconnected network framework. The as-prepared sample (NPCC2-700) shows desirable specific surface area of 2604.7 m2 g−1, large pore volume, and abundant micropores and mesopores. Combined with the high content of active heteroatoms, NPCC2-700 exhibits high specific capacitance of 311 F g−1 at 1 A g−1 and 250 F g−1 at 50 A g−1 in 6M KOH electrolyte. Meanwhile, the excellent rate performance and long-term cycling stability can be achieved for NPCC2-700. Furthermore, the energy density of the assembled symmetric supercapacitor based on NPCC2-700 electrodes is as high as 20.5 Wh kg−1 at a power density of 448.8 W kg−1 in 1 M Na2SO4 solution.