Electrolyte performance of green synthesized carbon quantum dots from fermented tea for high-speed capacitors

In recent years, obtaining carbon nanomaterials from natural products by natural methods has been among the most popular topics. The materials synthesized by this way have beneficial properties such as biocompatible, photostable and less harmful for environment. In this study, carbon quantum dots (CQDs) were synthesized by using fermented tea as a natural material and carbon source. The capacitor performance as an electrolyte was investigated with high-speed charge-discharge method as unusual in the literature. The characterizations of the CQDs were realized by HRTEM, XRD, XPS, UV-Vis absorption, and fluorescence spectroscopy techniques. The resulting particles have a size of about 10 nm according to HRTEM image. While the structural properties of the CQDs were confirmed by XRD and XPS, and optical behaviors were confirmed by UV-Vis and fluorescence spectroscopies. The electrochemical behavior of the obtained CQDs was tested as electrolyte material for capacitor applications. Experiments were carried out in three different operating potential windows in the 0-2 V range, and CQDs electrolytes exhibited high capacitive effect in symmetrical capacitors. However, the cyclic voltammetry (CV) analyses revealed that the CQDs electrolytes displayed a full supercapacitor electrolyte feature in the 0-0.5 V range. The CQDs electrolytes have a promising material for technological and industrial applications with their unique redox performance and high capacitive effect.