Ultra-small vanadium nitride quantum dots embedded in porous carbon (VNQDs/PC) were fabricated by a thermal treatment process of NH4VO3/C3H6N6 under nitrogen atmosphere. The specific capacitance of VNQDs/PC was 1008 mF cm(-2) at a current density of 0.004 A cm(-2), whereas the VN/carbon hybrid material obtained by a solid-state blending of NH4VO3 and C3H6N6 just exhibited a capacitance of 432 mF cm(-2) at the same current density. By mediating the ratio of NH4VO3 and C3H6N6, a maximum specific capacitance of 1124 mF cm(-2) was achieved at a current density of 0.002 A cm(-2) in aqueous 6 mol/L KOH electrolyte with the potential range from 0 to -1.15 V when it reached 1:7 (wt./wt.). Additionally, symmetrical supercapacitor fabricated with synthesized VNQDs/PC presented a high specific capacitance of 215 mF cm(-2) at 0.002 A cm(-2) based on the entire cell, and exhibited a high capacitance retention of 86.6% with current density increased to 5 A g(-1). The VNQDs/PC negative electrodes were combined with Ni(OH)(2) positive electrodes for the fabrication of hybrid supercapacitors. Remarkably, at a power density of 828.7 W kg(-1), the device delivered an ultrahigh energy density of 47.2 Wh kg(-1). (C) 2016 Elsevier B.V. All rights reserved.