In general, the specific capacitance of carbon materials shows the limited volumetric capacitance value with 400 F cm -1 and gravimetric capacitance in the range of 10 -200 F g -1 (400 F g -1 in few cases). Though it is predicted that the EDL capacitance of 550 F g -1 could be achieved for graphene by utilizing its complete surface area (2630 m 2 g -1 ), it is proven to be challenging/difficult in practice to obtain a monolayered graphene from graphene oxide by either chemical or thermal reduction method. The factors behind the limited supercapacitor performance of carbon-based materials are due to the following reasons: (i) In EDLC, the number of delocalized electrons from conducting band per atom is around 0.17-0.2, whereas in the case of electroactive pseudocapacitor materials, this is around 2.5 per atom depending on the oxidation states. In conventional batteries comprising of bulk phase electrode materials, nearly 1-3 localized electrons per atom can be stored by redox reactions ; Excessive increase of surface area (A) results in lowered mesoporosity, reduced carrier density, higher pore volume and thus leads to decreased charge storage capacity, eventhough the EDL capacitance is directly proportional the surface area of electrode (Cdl = εA/d). The specific capacitance becomes saturated if the surface area is increased above 1200 m 2 g -1 , calculated using density-functional theory (DFT), which is in accordance with the estimated Brunauer-Emmett-Teller (BET) surface area of 1500 m 2 g -1 . The carbon materials show lowered specific capacitance while introducing the porosity beyond certain level, and in addition the higher surface area often reduces the volumetric capacitance of supercapacitor and is not favourable for high-power operation ; (iii) Inspite of owning a higher surface area, carbon materials possess limited density of states at the Fermi level, and inadequacy of space to accommodate the charge carriers within the pores. The spatial confinement restricts the spacecharge capacitance, which is due to the screening of electrolyte charge in the inner layers by outer layers since carrier density of each layers follows an exponential depends on the screening length (λ) ≈ exp (-x/ λ). As a result, total capacitance of carbon materials is lowered (1/Ctotal = 1/CQ + 1/CSC + 1/Cdl) ; (iv) The adsorption of a thin layered hydrocarbon impurities of about 5-8.5 Å on the surface of carbon causes a dielectric dead layer, which introduces the series capacitance in supercapacitors. The dielectric dead layer is a layer of very low dielectric constant between the charge on electrode surface and the electrolyte, and it results in reduced specific capacitance ; (v) Low packing density of carbon materials results in poor interaction with electrode, as it leads to low volumetric energy density, chemical inertness, and hydrophobicity of carbon materials in aqueous electrolyte.