Chao Liu et al. synthesized the phosphorus doped carbon nanofibers by electrospinning and the subsequent annealing at 800 °C for 1h with different amounts of polyphosphoric acid solution (PPA) . Significantly, the SBET of P-PCNFs-1 was found to be 462.83 cm 2 g -1 which is comparatively higher than pristine PAN (298.3 cm 2 g -1 ) and the content of nitrogen and phosphorus in P-PCNFs-1 estimated from XPS analysis found to be 4.04 and 0.37 at. %, respectively. Among the various samples, the P-PCNFs-1 has delivered the maximum specific capacitance of 228.7 F g -1 at 0.5 A g -1 in 1 M H2SO4 solution which suggesting that the interfacial capacitance as well as the pseudocapacitive behavior enhanced due to phosphorus doping. Furthermore, the optimised material was assembled as a symmetric supercapacitor cell and attained the working voltage of 1.4 V in 1 M H2SO4 which is higher than 1.23 V for the decomposition of water. The expanding the working voltage might be due to the fact that the unstable electrochemically active sites are blocked by phosphorus functionalities that supresses the reduction in capacitance linked with oxygen atoms.