A facile potassium chloride salt-locking technique combined with hydrothermal treatment on precursors was explored to prepare nitrogen-doped hierarchical porous carbon sheets in air from biomass. Benefiting from the effective synthesis strategy, the as-obtained carbon possesses a unique nitrogen-doped thin carbon sheet structure with abundant hierarchical pores and large specific surface areas of 1459 m(2) g(-1). The doped nitrogen in carbon framework has a positive effect on the electrochemical properties of the electrode material, the thin carbon sheet structure benefits for fast ion transfer, the abundant meso-pores provide convenient channels for rapid charge transportation, large specific surface area and lots of micro-pores guarantee sufficient ion-storage sites. Therefore, applied for supercapacitors, the carbon electrode material exhibits an outstanding specific capacitance of 451 F g(-1) at 0.5 A g(-1 )in a three-electrode system. Moreover, the assembled symmetric supercapacitor based on two identical carbon electrodes also displays high specific capacitance of 309 F g(-1) at 0.5 A g(-1), excellent rate capacity and remarkable cycling stability with 99.3% of the initial capacitance retention after 10,000 cycles at 5 A(-1). The synthesis strategy avoids expensive inert gas protection and the use of corrosive KOH and toxic ZnCl2 activated reagents, representing a promising green route to design advanced carbon electrode materials from biomass for high-capacity supercapacitors. (C) 2018 Published by Elsevier Inc.