Preparation of Organic Molecule/N, P-Codoped Graphene Hydrogel Composites and Their Energy Storage Properties

Heteroatom doping is an efficient method to improve the hydrophilicity of the materials and regulate the electrical structure of adjacent atoms. In this work, the graphene hydrogel (GH) is first codoped with N and P atoms to improve its hydrophilicity, conductivity, and capacitance. Subsequently, quinoline 2,3-dicarboxylic acid (QDC) is modified on the surface of the N-P-GH by the π–π interaction to obtain a new composite material, QDC/N-P-GH. The specific capacitance of the obtained composite electrode materials can reach up to 838 F·g–1 at 1 A·g–1, which is much higher than that of most organic small-molecule electrodes. According to Density functional theory (DFT) calculations, the doping of the GH with N and P atoms significantly reduces the adsorption energy of organic molecules, which is more favorable to the stable adsorption of organic molecules. In order to evaluate the practical application of QDC/N-P-GH, a new negative material (DTAQ/GH) is also prepared by modifying the GH with 1,8-dichloroanthraquinone (DTAQ). Finally, an asymmetric supercapacitor is constructed by using QDC/N-P-GH as the positive material and DTAQ/GH as the negative material. The specific capacitance of this asymmetric device is up to 187.5 F·g–1 (1 A·g–1). The energy density (E) can reach 65.1 Wh·kg–1 when the power density (P) is 780 W·kg–1. This work provides a new idea to improve the capacitive properties of organic small molecule/graphene composites.