Display omitted 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 (SBET = 2010.1 m2 g−1 and Vmeso = 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.