Facile synthesis of g-C 3 N 4 quantum dots/graphene hydrogel nanocomposites for high-performance supercapacitor.

This work demonstrates a facile one-pot method for preparing graphitic carbon nitride (g-C 3 N 4 ) quantum dots/graphene hydrogel (CNQ/GH) nanocomposites using a hydrothermal process, in which graphene sheets of a graphene hydrogel (GH) are decorated with g-C 3 N 4 quantum dots (CNQDs) and have a 3D hierarchical and interconnected structure through a typical self-assembly process. The obtained CNQ/GH nanocomposite demonstrates improved electrochemical performances of a supercapacitor with a specific capacitance of 243.2 F g -1 at a current density of 0.2 A g -1 . In addition, the fabricated symmetric supercapacitor (SSC) using CNQ/GH electrodes exhibits a high energy density of 22.5 W h kg -1 at a power density of 250 W kg -1 and a superior cycling stability with a capacitance retention of 89.5% after 15 000 cycles. The observed improvements in the electrochemical performance of CNQ/GH electrodes are attributed to the large surface area with abundant mesopores and various C-N bonds in CNQDs, which promote efficient ion diffusion of electrolyte and electron transfer and provide more active sites for faradaic reactions. These obtained results demonstrate a facile and efficient route to develop potential electrode materials for high-performance energy storage device applications.