Supercapacitor performance based on nitrogen and sulfur co‐doped hierarchically porous carbons: Superior rate capability and cycle stability

Herein, the banana-peel waste was carbonized followed by KOH activation to design novel N, S-co-doped hierarchically porous carbonaceous materials (NS-AC). The synthesized sample (NS-AC) exhibited an interconnected porosity and endowed with a high specific surface area (SSA ~ 2452 m2 g−1), total pore volume (Vtotal ~ 1.82 cm3 g−1), and moderate nitrogen (3.2 at%) and sulfur (0.6 at%) contents. Moreover, these carbons, when scrutinized as electrode materials, demonstrated a specific capacitance (220 F g−1 at 0.5 A g−1), which persists at 145 F g−1 even at a large current density of 6 A g−1, thereby demonstrating an efficient rate capability. Furthermore, a capacitance retention of ~78.2% over 15 000 cycles was also observed. All these characteristics reveal NS-AC carbons a promising contender for energy storage. Finally, as-prepared symmetric supercapacitor (NS-AC/NS-AC) exhibited remarkable energy density ~5.3 Wh kg−1 at a power density of 2690 W kg−1 with capacitance retention of 88% over 4000 charge/discharge cycles, which surpasses the working performance of the many reported carbon materials obtained from biomass sources. In conclusion, outstanding textural features and enhanced conductivity by KOH activation, in addition to the improved surface wettability posed by N- and S-enriched surfaces, resulted in considerable supercapacitor performance. Highlights Banana peels-derived biochar-based porous carbons Porous carbons exhibit large specific surface area (>2452 m2 g−1). Binary heteroatom-doped carbons possess at% of N (3.2) and S (0.6). Synergetic effect of N and S doping and high porosity leads to high supercapacitance.