Graphene fabricated by different approaches for supercapacitors with ultrahigh volumetric capacitance

Nanoporous structure and high surface area of graphene affords low volumetric capacitance when used as a supercapacitor. In this study, four different facile and economical fabrication techniques are reported for producing graphene nanosheets with high packing density. Successful fabrication was verified via X-ray diffraction, Fourier transform infrared analysis, and Raman spectroscopy. The as-prepared samples possess a compact layered structure with a packing density of 1.74–1.95 g cm⁻³, which is 79%–88.6% that of graphite density. Ultrahigh volumetric capacitances of 696 and 540 F cm⁻³ were obtained for graphene samples prepared via electrochemical exfoliation and solvothermal reduction methods, respectively (with excellent stability behavior of 103% after 9000 charge–discharge cycles). These volumetric capacitance care the highest values reported thus far for carbon materials in an aqueous electrolyte. These values were attained without any material addition and/or functionalization. A symmetric supercapacitor device assembled for the sample produced via electrochemical exfoliation achieved a volumetric capacitance of 204.5 F cm⁻³ with a high energy density of 16.3 Wh kg⁻¹ at 0.3 A g⁻¹ in 6 M KOH. The supercapacitor device exhibited high stability, retaining ~89% of the original specific capacitance after 3000 charge–discharge cycles. These findings indicate that selecting a siutable graphene fabrication technique corresponding to the required application is crucial. For the present study, graphene materials produced through solvothermal reduction and electrochemical exfoliation are promising for fabricating compact, high-energy, and high-power supercapacitors.