Besides, the oxygen content of BHAC-800 (11 at. %) is greater than that of BAC-800 (7 at. %). Thus, it has been proposed that hydrothermal treatment under acidic condition prior to activation enhances both the surface area as well as oxygen content that facilitated the wettability of the electrode and giving rise to the amplified capacitance. Also, the BHAC-800 fabricated symmetric supercapacitor delivered the capacitance retention of 90% from its original value after 1000 cycles. in 2 M KOH aqueous solution found to be 342 F g -1 which is greater compared to P-C (77 F g - the larger pore volume of 2191 and 1.034 cm 3 g -1 , respectively. Moreover, the oxygen content of P-AC and H-AC determined from XPS analysis found to be 15.28 and 9.2 at. %, respectively. Thus, it was concluded that not only the surface area as well as porosity generated as a result of KOH activation but also the presence of oxygen functionalities is presumed to be responsible for the augmented capacitance of the carbon-based materials. the oxygen enriched hierarchical porous carbon (HPC-KOH) by the activation of KOH with hierarchical porous carbon in the mass ratio of 2:1 at 700 °C for 1 h under the flow of N2 gas . Indeed, the hierarchical porous carbon (HPC) was prepared by the carbonization of artemia cyst shells at 300 °C for 3 h and 700 °C for 4 h and the subsequent treatment with 67 wt% nitric acid for 1 h 20 minutes. The HPC-KOH achieved a gravimetric capacitance of 369 F g -1 at 0.5 A g -1 in 1 M H2SO4 solution which is relatively higher than HPC (321 F g -1 ). The same trend is also followed in 6 M KOH solution at 0.5 A g -1 such that the gravimetric capacitance of HPC-KOH (349 F g -1 ) is superior than HPC (297 F g -1 ) and also agree well with appearance of redox humps in the CV profile due to the participation of oxygen functionalities as exhibited in Fig. and, respectively. This might be accounted for the fact that the SBET of HPC-KOH (1758 m 2 g -1 ) is larger than HPC (455 m 2 g -1 ). Besides, the oxygen content of HPC-KOH found to be 13.1 at. % which is faintly lesser than HPC F g -1 at 1 A g -1 in 6 M KOH aqueous solution as the electrolyte and higher than that without activation with KOH (PAC-800) delivering the value of 196 F g -1 as the SBET of the former (2988 m 2 g -1 ) is higher than the latter (1315 m 2 g -1 ). Also, the content of oxygen in KPAC-800 estimated to 8.9 at. % which is higher than that of PAC-800 (6 at. %). The KPAC-800 based symmetric cell displayed an enhanced capacitance of 238 F g -1 at 0.2 A g -1 which is higher than RP20 (132 F g -1 at 0.2 A g -1 ) along with 97.5% of retention of capacitance after 15000 cycles at 3 A g -1 and displayed in Fig. and, respectively. Moreover, the energy density of 31.7