Integrated gas expansion and activation strategy to prepare shaddock peel-derived nitrogen doped honeycomb carbon for high performance supercapacitor

Shaddock peel-derived nitrogen doped honeycomb carbon (NHPC) has been prepared by a facile integrated gas expansion, activation and nitrogen doping strategy using urea and potassium carbonate (K 2 CO 3 ) as the mixed activating agents. The thermal decomposition of urea to generate ammonia plays a dual role of a nitrogen source and gas expanding agent, while the K 2 CO 3 plays a pore-creating medium. The NHPC exhibits honeycomb-like microstructure feature and possesses a large specific surface area (1438.5 m 2  g −1 ), high nitrogen doping (6.23 wt%) and well-developed mesopores. Consequently, the NHPC used as electrode for supercapacitor exhibits high specific capacitance of 225 F g −1 at 0.25 A g −1 and good rate capability. In addition, the symmetric supercapacitor fabricated with NHPC material in 1 M K 2 SO 4 aqueous electrolyte delivers high energy density of 18 W h kg −1 operated in the wide voltage of 2.0 V and superior cyclability of 97.8% capacity retention after 30,000 cycles.