Rational Design of NiCo₂S₄ Nanosheet Arrays Modified by Nitrogen-Doped Graphene Quantum Dots with Enhanced Charge Storage Performance for Flexible Supercapacitors

In this work, nitrogen-doped graphene quantum dots (N-GQDs) are introduced into the honeycomb structure of NiCo2S4 nanoarrays on a carbon cloth by electrodeposition, which significantly enhances the electrochemical performances of NiCo2S4 as an electrode of hybrid supercapacitors. The honeycomb framework structure of NiCo2S4 nanosheets not only increases more active sites but also improves the structural stability of the electrode material. At the same time, the introduction of N-GQDs improves the wettability of NiCo2S4 and effectively reduces its internal resistance. As an electrode material, the NiCo2S4/N-GQDs@CC composite shows outstanding capacitive properties with an areal capacity of 1803 mC cm–2 at 3 mA cm–2. In addition, the assembled symmetric supercapacitor device can provide a high energy density of 127 μWh cm–2 at a power density of 1000 μW cm–2, good rate performance, and cycle stability. After 2500 cycles, the capacity retention rate can still reach 83%. The outstanding charge storage capability may be due to the synergistic effect between its unique honeycomb structure, high porosity, and improved electrical properties of N-GQDs. This simple and controllable synthesis strategy provides a reference for energy storage applications.