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.