N-enriched mesoporous carbon nanofibers (NMCNFs) were prepared by an electrospinning technique using graphitic carbon nitride (g-C3N4) nanosheets both as sacrificial template and N-doping source. The resultant NMCNF film has a high N-doping level of 8.6 wt% and a high specific surface area of 554 m(2) g(-1). When directly used as the electrode material for supercapacitor, the free-standing NMPCNF film shows a significantly improved capacitive performance including a higher specific capacitance (220 F g(-1) at 0.2 A g(-1)) and a better rate capability (similar to 70% retention at 20 A g(-1)) than those of microporous carbon nanofiber film prepared using the same process without using g-C3N4 nanosheets (145 F g(-1) at 0.2 A g(-1) and similar to 45% retention at 20 A g(-1)). Moreover, the NMCNFs show superior stability with only a similar to 3% decrease of its initial capacitance after 1000 cycles at a high current density of 10 A g(-1). More significantly, the energy density of a symmetrical supercapacitor (SC) based on the NMPCNF film can reach 12.5 Wh kg(-1) at a power density of 72 W kg(-1). (C) 2015 Elsevier Ltd. All rights reserved.