Buckwheat husk-derived hierarchical porous nitrogen-doped carbon materials for high-performance symmetric supercapacitor

A facile one-step strategy is established to prepare nitrogen doped three-dimensional (3D) hierarchical porous carbon from buckwheat husk, in which the synchronous activation and nitrogen-doping is fulfilled via using KOH and urea. The obtained sample (BSCN-700) possesses an ultrahigh specific surface area of 2794.5 m2 g−1 with a unique carbon frame. The electrochemical measurements indicate that the resultant BSCN-700 exhibits a high specific capacitance of 326 F g−1 at current density of 1 A g−1, with good rate capability (78.4% capacitance retention at 100 A g−1) in 6 M KOH electrolyte. Furthermore, the as-prepared sample was used to assemble a symmetric supercapacitor filled with 6 M KOH electrolyte. As a result, the BSCN-700 symmetric supercapacitor displays a high energy density of 20.4 Wh kg−1 at a power density of 699 W kg−1 and good cycling stability which retains 95% of the initial capacitance at 5 A g−1 after 5000 cycles.