▎ 摘　　要

Sandwich-like nitrogen-enriched porous carbon/graphene composites were prepared by carbonization of polyacrylonitrile (PAN) nanofiber paper with bulk-doped and/or surface-coated graphene oxide (GO), and followed by activation with KOH at high temperatures. The composites exhibit high specific surface areas in a range of 1957.2-2631.8 m(2) g(-1), as well as superior energy storage capability as electrodes for supercapacitors. A very high specific capacitance of 381.6 F g(-1) at a current density of 0.1 A g(-1) was achieved in 6 M KOH aqueous electrolyte for N-ACGrF@Gr1 that contains two types of graphene. According to the investigation results, the surface-coated graphene plays a more positive effect on improved supercapacitance than the bulk-doped graphene in the composites. Additionally, the assembled aqueous symmetric supercapacitors deliver a high energy density of 13.2 W h kg(-1) at a power density of 25.0 W kg(-1), and 8.3 W h kg(-1) at 4.7 kW kg(-1) with a retention rate of 62.9%. (C) 2015 Elsevier Ltd. All rights reserved.