The obtained co-doped material has achieved 94% retention in capacitance from its initial value over 12000 cycles at 2 A g -1 . Furthermore, the NSeGA based symmetric supercapacitor exhibits a high energy density of 26.3 W h kg -1 at a power density of 900 W kg -1 in 1 M Na2SO4 aqueous electrolyte with the operating cell voltage of 1.76 V. Due to the doping by the two heteroatom such as N and Se, the pseudocapacitance behavior of N, Se co-doped graphene is enhanced to the greater extent. In addition, the wettability of the electrode is improved owing to the fact that the electronegativity of nitrogen is higher than carbon and selenium. In another KOH solution which is appreciably greater than HACNTs (378 F g -1 ). It was found that the oxygen and nitrogen content of ACNTs analysed from XPS were found to be 15.72 and 2.97 at. % which is higher than those of HACNTs having the oxygen and nitrogen content of 6.93 and 1.38 at. %, respectively. Thus, it has been proposed that both the oxygen as well as nitrogen containing groups such as quinone, pyridinic and pyrrolic played a major role in the (1472 F g -1 ). Also, the 99% of capacitance retained after 300 cycles for the hybrid (3DNi foam/NiCo2O4 with N-CNTs). The 3D Ni foam/ N-CNTs/NiCo2O4 attained the 81% of capacitance retained of its initial value after 9000 cycles and displayed in Fig. . The CV profile of first cycle and 9000 th cycle for the hybrid revealed that the area under the CV profile for the latter is faintly smaller than the former implying that the mild reduction in capacitance was observed and displayed in Fig. . From Fig. , it was clearly seen that the 3D structure is not perturbed indicating the excellent stability. Thus, the outstanding electrochemical performance of the hybrid was attributed to the three-dimensional conducting network of N-CNTs that promotes the fast movement of electrons and the abundant electroactive sites of the interconnected morphology of NiCo2O4 which permit easier diffusion path for the quick transport of ions. and 215 F g -1 at 0.2 A g -1 in 1 M H2SO4 aqueous solution, respectively. Furthermore, the specific capacitance of N-doped CNT in spherical form is higher compared to film and displayed in Fig. . It has been suggested that the increased content of nitrogen and the existence of mesopores in spherical particles that furnish the rapid transport of ions are presumed to be responsible for the improved capacitance of high N-doped CNTs. Our group has previously adopted the CVD assisted preparation of N-doped CNTs using a mixture of acetylene and ammonia with LaNi5 alloy as a catalyst accompanied by treatment with the mixture of 3M nitric acid and sulphuric acid . The acid treatment leads to opening of CNTs that give rise to increased performance in capacitive behaviour compared to assynthesized N-doped CNTs and evidently shown in Fig. that the area under the CV curve for acid-treated N-CNTs is higher compared to as-obtained one. The calculated specific capacitance of N-doped CNTs is found to be 146 F g -1 which is 3.4-fold higher compared to as-synthesized CNTs (42 F g -1 ) in 1 M KCl solution as the electrolyte. The N-doping content of acid -treated N-CNTs (7.3 at. %) is slightly higher than as-synthesized N-CNTs (6.7at. %).