Nitrogen-enriched porous carbon nanofibers were successfully prepared by using water-soluble phenolic resin/polyvinyl alcohol blend solution as precursor via electrospinning followed by carbonization and NH3 treatments. The NH3 treatment time has a significant effect on the pore structure, thermal stability as well as the surface chemistry. The as-prepared carbon materials were studied as freestanding electrodes for supercapacitor without the addition of binders and conductive additives in 6 M KOH solution. The sample treated with NH3 for 3 h exhibits a high specific surface area (763 m(2) g(-1)), rich surface functionalities (5.26 at.% nitrogen and 4.37 at.% oxygen), optimized pore structure, good thermal stability and electrical conductivity. It shows the maximum specific capacitance of up to 251.2 F g(-1) at 0.1 A g(-1), about 25% higher than that of the sample treated with argon. Furthermore, the specific capacitance remains 193 F g(-1) at 20 A g(-1) with high rate capability of 77%, as well as excellent cycle stability (99% capacity retention after 2000 cycles). The outstanding performance of nitrogen-doped porous carbon nanofibers could be attributed to the synergistic effect of the proper pore size distribution, high effective surface area and certain amount of nitrogen-and oxygen-containing functional groups, resulting in both electrochemical double layer and faradaic capacitance contributions. (C) 2015 Elsevier Ltd. All rights reserved.