Quinoline-2,3-dicarboxylic Acid-Modified Graphene Hydrogel Composites for High-Performance Asymmetrical Supercapacitors

Small organic molecules with electrochemically active functional groups can achieve high-density energy storage by the reversible Faraday reaction of multiple electrons. However, poor conductivity has hindered their wide application in the field of energy storage. Graphene hydrogel (GH), a graphene derivative, has a three-dimensional porous network, and the three-dimensional network efficiently releases graphene’s true surface by preventing graphene from building up. Therefore, compared with graphene, graphene hydrogels are more suitable as substrate materials. In the present article, the small organic molecule quinoline-2,3-dicarboxylic acid (QDC) is successfully modified on GH by a hydrothermal method to obtain a carbon-based electrode material, QDC/GH. QDC/GH displays excellent capacitive property with a specific capacitance of 512 F g –1 at 1 A g –1 . Importantly, the cycling stability test indicates that the capacitance retention is close to 99% after 10,000 cycles at 5 A g –1 . To explore the practical implementation of QDC/GH, an asymmetric supercapacitor QDC/GH//AC is assembled, which uses QDC/GH as the positive electrode material and activated carbon (AC) as the negative electrode material. Compared with other devices, the device shows a high energy density, reaching 37.7 W h kg –1 at a power density of 905 W kg –1 . The energy density is higher than that of most of the organic molecular capacitors that have been reported. In addition, two devices can be used in series to light 52 LED bulbs. By organic molecular modification, GH’s capacitance performance can be further improved, and its application to energy storage can be further expanded.