Graphene (5−11) possesses a high surface area (2630 m 2 g –1 for monolayer graphene) compared to amorphous carbon that can be utilized for the accumulation of ions within the EDL and thus significantly increase the capacitance of the electrodes.
Graphene is a robust and attractive electrode material for supercapacitors because of its excellent electrical conductivity, high surface-to-volume ratio, and outstanding intrinsic double-layer capacitance (21 μF cm −2) or theoretical capacitance (550 F g −1) 21, 22, 23, 24, 25, 26, 27.
Some of experimentally reported capacitance for graphene based/ derived supercapacitors vary in the ranges of 80–394 μ F / cm 2 and 75–205 F/g , , , . The device geometry with optimal separation parameters for graphene capacitor is depicted in Fig. 1 a.
The geometric capacitance of the top-gate was estimated to be C g ≈ 6 fF μ m - 2. Effective surface area of graphene as an electrode material is much lower than that of the theoretical value due to agglomeration and restacking by the van der Waals interactions between neighboring sheets.
While graphene with high surface area can enhance the double-layer capacitance, its low quantum capacitance limits its application in supercapacitors. This is a direct result of the limited density of states near the Dirac point in pristine graphene.
For instance, the theoretical specific capacitance of single-layer-graphene is ∼21 uF cm −2 and the corresponding specific capacitance is ∼550 F g −1 when the entire surface area is fully utilized .