This was also confirmed with EIS analysis indicating that the Rct value determined from the EIS Nyquist plot of N-doped CNT@CNF hybrid (2.22 Ω) is drastically lower than CNT@CNF hybrid . Furthermore, the N-doped CNT@CNF hybrid based symmetric cell accomplished a gravimetric capacitance and energy density of 155 F g -1 and 5.5 Wh Kg -1 in addition to the 93% of capacitance retained after 10000 cycles at 10 A g M KOH solution found to be 329 F g -1 and higher than Co/N-CNT @PCNF-900 (255 F g -1 at 0.5 A g -1 ) which might be due to the SBET of former (789.2 m 2 g -1 ) is larger than the latter (505.6 m 2 g -1 ). Also, 96% of capacitance retention is achieved after 10000 cycles and exhibited in Fig. respectively. The same material delivered the maximum specific capacitance of 314 F g -1 at 1 A g -1 and 61 F g -1 at 0.5 A g -1 by three and two electrode system, respectively. It has been suggested that increased surface area furnish transmission channels for the transport of ions towards the electrode surface and higher doping content impart electroactive centers that might be possible reasons for the improved capacitance. As the optimised ratio (N-CNT@HCNF-1.5) delivered a superior specific capacitance of 712 F g -1 at 1 A g -1 in 2 M KOH solution by three-electrode system, the same was fabricated as a flexible all-solid-state-symmetric supercapacitor in PVA-KOH/gel electrolyte and attained a high energy density of 20.13 Wh Kg -1 along with 98.9% capacitance retention from its original value after 10000 cycles. The calculated SBET of N-CNT@HCNF-1.5 is found to be 812.6 m 2 g -1 that might be the possible reason for the enhanced capacitance.