[861]. It was observed that the SBET rises from activated carbon at 500 °C (546 m 2 g -1 ) to the activated carbon at 600 °C (2598 m 2 g -1 ) and again decreases to 592 m 2 g -1 for the activated carbon at 900 °C. Also, it was found that the SBET enhances with increase in the mass ratio of KOH. Among the different set of samples, the activated carbon prepared in the mass proportion of carbonized version of elm seeds with KOH in 1:6 obtained at 600 °C with the highest oxygen content of 32.95 at. % from XPS achieved the amplified gravimetric capacitance of 501 F g -1 at 1 A g -1 in 6 M KOH aqueous solution and 95.8% of retention of capacitance after 10000 cycles. Moreover, the symmetrical supercapacitor derived from the activated carbon of elm seeds obtained at 600 °C accomplished the energy density of 18. carbon from the activation of NaOH to coconut coir pith (CCP) char in the weight ratio of 1:1, 2:1 and 3:1 at 700 °C about 60 minutes [862]. Among these, the AC-3 where the weight ratio of NaOH to CCP char in 3:1 has delivered the maximum specific capacitance of 232.3 F g -1 at 0.1 A g -1 in 1 M H2SO4 solution as it got the maximum SBET and pore volume of 2056 m 2 g -1 and 1.17 cm 3 g -1 , respectively. Moreover, 95.4% of capacitance retained after 5000 cycles at 0.5 A g -1 . XPS investigations revealed the presence of oxygen functional groups that is also responsible for the upgraded capacitance.