Nanocomposites of graphene and N-doped porous carbon (HPNCs/rGO-800) are prepared via facile carbonization of Zn-metal-organic frameworks (ZIF-8) by controlling appropriate temperature. In comparison with the single N-doped porous carbon (HPNCs-800) which are made from the pure ZIF-8, HPNCs/rGO-800 reduce the agglomeration of ZIF-8 and promote electrical conductivity. In this work, HPNCs/rGO-800 materials exhibit excellent electrochemical performances with a high specific capacitance of 245 F g(-1) in 6 M KOH electrolyte at a current density of 1 A g(-1). Moreover, HPNCs/rGO-800//HPNCs/rGO-800 symmetric supercapacitor reaches a superior energy density of 18.0 Wh kg(-1) at a power density of 475 W kg(-1) in the wide voltage region of 0-1.8 V, and a superb cycle stability (90% capacitance retention after 10,000 cycles). Such outstanding electrochemical behavior shows that the device is a promising practical energy-storage facility. (C) 2017 Elsevier Ltd. All rights reserved.