To widen the practical application of supercapacitors in acid electrolyte, carbon/molybdenum nitride (C/MoxN) nanofibers are synthesized via combination of electrospinning method and thermal treatment in mixed gas atmosphere of N-2 and NH3. When the mass fraction of ammonium molybdate of 1.13 wt.% is added in the precursor mixture solution, as-prepared C/MoxN composite shows the nanofibers of about 200 nm diameter with MoxN nanoparticles uniformly embedded in the N-doped carbon substrate, and delivers a specific capacitance of 251 F g(-1). Three types of supercapacitor devices of PANI parallel to C/MoxN, AC parallel to C/MoxN and C/MoxN parallel to C/MoxN are configured in acid electrolyte. The asymmetric supercapacitor of PANIjjC/MoxN shows a maximum energy density of 14.1Wh kg(-1) and power density of 312Wkg(-1), which was larger than those of AC parallel to C/MoxN device (12Wh kg-(1,) and 325Wkg(-1)) and symmetric supercapacitors of C/MoxN parallel to C/MoxN device (4.51Wh kg(-1), and 250Wkg(-1)). The C/MoxN parallel to C/MoxN device exhibits good cycle life of specific capacitance retention of 78.6% at 2 A g(-1) after 15, 000 cycles. (C) 2018 Elsevier Ltd. All rights reserved.