Giant energy storage capacity of graphene quantum dots prepared by facile method

Abstract

Supercapattery technology focuses on high specific capacity with both high energy density and power density. In the present work, the electrochemical performance of Graphene quantum dots (GQDs) is compared with graphene oxide (GO). GO is synthesized by the modified Hummer's method. Less than 5 nm size of GQDs are synthesized by a facile chemical cutting method. High frequency vibrational mode of sp-sp2 bonded carbon at 2198 cm−1 is revealed from Raman analysis. The energy gap of GQDs of different sizes was calculated using the Quantum Espresso code based on Plane-Wave Self-Consistent Field (PWSCF). The forbidden gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels with the size of the GQDs cluster. The electrochemical results show that GQDs exhibit pseudocapacitor behavior with high specific capacity and energy density of 1516.7C/g and 425.9 Whkg−1 respectively at current density of 4 A/g. This is very high compared to the electric double layer capacitor (EDLC) behavior (115C/g) of GO. These results illustrate enhanced electrochemical performance, electrical conductivity and ion transport rate implying that the material can facilitate the movement of ions within the device, allowing for fast charging and discharging.