Nitrogen-doped sandwich-like porous carbon nanosheets (NPCG) have been prepared simply through carbonization of graphene/polyaniline hybrid materials. Due to its interconnected microporous structure, high nitrogen content (12.7 at.%), high surface area (410.4 m(2) g(-1)) and high volumetric density (0.94g cm(-3)), the obtained sample prepared at 700 degrees C (NPCG-700) shows both high gravimetric and volumetric capacitances of 305 F g(-1) and 287 F cm(-3) in 6M KOH aqueous electrolyte, respectively. In addition, the assembled supercapacitor delivers a high energy density (16.3 Wh kg(-1) and 15.3 Wh L-1) in 1 M Na2SO4 aqueous electrolyte. Importantly, 97% of the initial capacitance is maintained after 5000 cycles, suggesting excellent cycling stability. (C) 2014 Elsevier Ltd. All rights reserved.