Hydrothermal Synthesis of Graphene Quantum Dots Supported on Three-Dimensional Graphene for Supercapacitors

Abstract

Incorporation of new functional components into a three-dimensional graphene (3DG) framework improves the performance of supercapacitors based on 3DG as electrodes by tailoring the framework’s structure and properties. In this work, graphene quantum dots (GQDs) were incorporated into 3DG via one-step hydrothermal treatment of GQDs and graphene oxide (GO). By simply adjusting the GQDs/GO feeding ratio by weight, various GQDs/3DG composites were formed. The maximum feeding ratio was 80%, and the prepared composites possessed saturated GQDs loading on the 3DG framework, whereas composites obtained with a GQDs/GO feeding ratio of 40% as electrodes exhibited optimal specific capacitance of 242 F·g−1 for supercapacitors, an increase of 22% compared with that of pure 3DG electrodes (198 F·g−1). This improved performance was mainly due to better electrical conductivity and larger surface area for GQDs/3DG composites with moderate GQDs content. The fabricated GQDs/3DG composites as electrodes for supercapacitors revealed high electrochemical stability. Their capacitance kept 93% of the initial value after 10,000 charge-discharge cycles.

Further Thermal Reduction of Reduced Graphene Oxide Aerogel with Excellent Rate Performance for Supercapacitors

“…They always remain in a typical rectangular shape when the scanning rate changes from 10 to 100 mV·s −1 . While the CV curves for the RGO hydrogel distorted rapidly when increasing the scanning rate [30]. Therefore, the obtained 3DG via thermal treatment possesses better rate performance for supercapacitors, and no obvious redox peaks relevant to oxygenated groups are seen, supporting the electrical double-layer capacitance for 3DG.…”

“…The intensity ratio of D and G bands (I D /I G ) reflects the defect extent of materials. The I D /I G value of prepared 3DG was measured to be 1.28, obviously higher than that of its RGO hydrogel precursor with a value of 1.04 [30], indicating sp 2 domains and edge defects were increased after thermal reduction [32]. C 1s XPS spectra of 3DG ( Figure 2b) reveal typical peaks at ca.…”

“…Lower oxygen content for 3DG was also demonstrated by the ratio of C/O measured by XPS. 3DG had a C/O ratio of 7.1:1, higher than that of RGO hydrogel of 6.2:1 [30]. The oxygenated groups were further removed from the 3DG via thermal reduction, improving its electrical conductivity.…”

“…Firstly, RGO hydrogel was prepared via hydrothermal reduction of GO according to our previous method [30]. The used GO aqueous solution of 2 mg·mL −1 with a sheet size larger 500 nm was purchased from Nanjing XFNANO Materials Tech.…”

“…The counter electrode was an RGO coated platinum plate. And the specific capacitance was calculated by galvanostatic charge/discharge (GCD) curves similar to our previous method [30].…”