Nitrogen-doped activated carbon (NAC) materials were prepared via a convenient and low-cost method from polyethylenimine (PEI) modifying commercial activated carbon (AC). After high-temperature treatment, nitrogen atoms were successfully introduced into the resulting AC matrix simultaneously the open porous structure of AC was well preserved. With the unique structure and heteroatom doping, the NAC material achieved a high capacitance value of 268 F g(-1) in symmetric supercapacitor device in acidic electrolyte, as well as 226 F g(-1) in organic electrolyte with 3 V voltage window. High energy density of 60.3 Wh kg(-1) obtained in NAC based supercapacitor device, suggesting the great potential for industrial application in energy storage field. (c) 2018 Elsevier Ltd. All rights reserved.