Kuiyong Chen et al. demonstrated the fabrication of heteroatom doped mesoporous carbon nanofibers (HMCNFs) by the one-pot polymerisation of hexachlorocyclotriphosphazene and p-toluene sulphonic acid in presence of TEA/THF and washing with triethyl amine hydrochloride accompanied by the thermal annealing at four various temperatures (700, 800, 900 and 1000 °C) [722]. Among the samples obtained at various temperatures, the HMNCNFs produced at 800 °C attained the maximum gravimetric capacitance of 214.9 F g -1 at 0.1 A g -1 in 6 M KOH solution. The atomic content of nitrogen, oxygen, phosphorus and sulphur in HMCNFs-800 evaluated from XPS found to be 1. It was illustrated that on increasing the annealing temperature, the content of heteroatoms such as nitrogen, oxygen, phosphorus and sulphur decrease while the SBET increases. Thus, it has been concluded that the decreased content of heteroatoms might be the probable reason for the decrement in the capacitance of HMCNFs because of the reduced pseudocapacitance by the doped heteroatoms at higher carbonization temperature. Guiyin Xu et al. prepared the porous N, P co-doped carbon nanofiber networks by 3D PANI nanofiber networks using phytic acid as the phosphorus source and the subsequent carbonization as well as chemical activation using KOH as the activating agent at 650 °C for 0.5 h under N2 atmosphere . The obtained porous N, P co-doped CNFs have delivered the specific capacitance of 280 F g -1 at 1 A g -1 in 6 M KOH solution with good capacitance retention of 94% after 10000 cycles. The ultrahigh SBET of 2586 m 2 g -1 would be the possible reason for the significant improvement in the capacitance compared to the sample without activation using KOH (421 m 2 g -1 ). Furthermore, the porous N, P co-doped CNFs based symmetric supercapacitor attained an energy density of 22.9 W h kg -1 at a power density of 325 W kg °C for 18 h followed by etching and supercritical drying . Thus, the as-prepared CNF aerogels were subjected to carbonization and subsequent activation with CO2 at 900 °C in different durations (0.5, 2, 4 and 6 h). It was found that both SBET and the content of nitrogen decreases with rise in the duration of activation with CO2. Among the variety of samples, the activated N-CNF obtained for 6 h attained the enhanced gravimetric capacitance of 250 F g -1 at 1 A g -1 in 6 M KOH solution owing to its high SBET of 1324 m 2 g -1 suggesting that the longer period for the CO2 activation enhances the population of micropores leading to the amplified surface area. . The electrospun polymer fiber/SiO2 was subjected to calcination at 800 °C about 2 h in nitrogen atmosphere. Among the different weight percentages of SiO2, the N-CNF prepared with 66 wt% of SiO2 at 800 °C attained the enhanced nitrogen content and the specific capacitance of 17.3 wt% and 242 F g -1 at 0.2 A g -1 in 1 M H2SO4 solution, respectively. Besides, 99% of original capacitance retained after 5000 cycles. It was observed that with increase of carbonization temperature of the polymer mat from 600 to 800 °C, the nitrogen content moderately decreases while the specific capacitance increases and represented in Fig. and. However, when the temperature is decreased from 800 to 900 °C then the drastic decrease in the capacitance was observed due to the significant reduction in the content of nitrogen from 12.4 to 6.6 wt. %. The electrochemical performance of the N-CNFs was mainly decided by the content of SiO2 in the precursor solution and the calcination temperature. % and 198 F g -1 at 1 A g -1 in 6 M KOH aqueous solution and greater than pristine (60 F g -1 ), respectively. The symmetric cell investigations revealed that it displayed the specific capacitance of 148 F g -1 at 1 A g -1 and 104% of capacitance from its original value retained after 5000 cycles. PVP function as a porogen to enhance the volume of micropores and enrich the content of nitrogen which is highly advantageous for supercapacitor. In another study, Chen et al. developed the hollow N-doped CNFs (H-NCNFs) by the electrospinning which involves the embedding of ZIF-8 nanoparticles into PAN nanofibers accompanied by thermal annealing at 900 °C under inert atmosphere . Thus, the obtained H-NCNFs with 9.39 wt% of nitrogen was assembled as a symmetric supercapacitor and delivered the maximum gravimetric capacitance of 307.2 F g -1 at 1 A g -1 in 2 M H2SO4 because of the larger SBET of 417.9 m 2 g -1 .