Hierarchical rapeseed stalk-derived activated carbon porous structure with N and O codoping for symmetric supercapacitor

The high specific surface area, excellent electrical conductivity, and chemical stability of porous carbon have increasingly garnered attention in supercapacitors. Herein, rapeseed stalks were utilized as precursors to synthesize nitrogen (N) and oxygen (O) co-doped porous activated carbon (RSAC) through processes of high-temperature carbonization and KOH activation. The optimally synthesized RSAC-10 exhibits an ultra-high specific surface area of 3085 m2 g−1, a specific capacitance of 354.7 F g−1 at 1 A g−1, and remarkable cyclic stability (105% of its specific capacitance after 10,000 cycles). Moreover, a symmetric supercapacitor (SSC) fabricated with RSAC-10 electrodes and a 6 M KOH electrolyte demonstrates a high specific capacitance of 85.21 F g−1 at a current density of 0.25 A g−1, maintaining 89.8% of its initial capacitance after 10,000 cycles. Additionally, an SSC comprising RSAC-10 electrodes and [BMIM]BF4 electrolyte delivers an energy density of 52.6 Wh kg−1 at a power density of 375.1 W kg−1. This work presents an effective method for valorizing crop waste and successfully prepares electrode materials with high specific surface areas alongside substantial energy and power densities.