Hierarchically porous and heteroatom self-doped graphitic biomass carbon for supercapacitors.

Here we report a simple, low-cost and environment friendly method, in which Black locust seed dregs and potassium ferrate (K₂FeO₄) are used as starting raw materials and activation agent. The hierarchically porous carbons (BDPC) with high special surface area and abundant mesopores (S_BET = 2010.1 m² g^-1 and V_meso = 1.457 cm³ g^-1) are obtained through hydrothermal treatment and chemical activation. The BDPC electrode exhibits excellent electrochemical performances by virtue of unique architecture and heteroatoms pseudocapacitance contribution. In the three-electrode system, the optimized carbon material (BDPC-2) achieves a high specific capacitance of 333 F g^-1 at 1 A g^-1 and displays the high rate capability (81.1% capacitance retention at 100 A g^-1) in 6 M KOH electrolyte. The symmetric supercapacitor based BDPC-2 exhibits energy density as high as 26.2 Wh kg^-1 (at a power density of 0.79 kW kg^-1) and excellent long-term cycling stability (only 8% decrease after 10,000 cycles) in 6 M KOH.