Constructing nitrogen-doped graphene quantum dots embedded in CNT supported layered (Ni_0.5Co_0.5)₃V₂O₈ self-supporting...

To improve the electrochemical performance of positive electrode materials, constructing graded nanostructures is a worthwhile approach. This study successfully synthesized nitrogen-doped graphene quantum dots (NGQD) modified (Ni_0.5Co_0.5)₃V₂O₈ on a carbon nanotube (CNT) substrate to construct self-supporting electrodes for high-performance supercapacitors. The (Ni_0.5Co_0.5)₃V₂O₈ nanosheets were successfully wrapped onto the CNT surface through a solution impregnation process, which increased the specific surface area and interlayer spacing of the material. Furthermore, the electrochemical properties of the electrode material underwent significant enhancement due to the synergistic interplay between metal ions and the numerous redox centers. The embedding of the NGQD enriched the materials with active sites and further improved its specific capacity without compromising the structure intergrity of the layer configuration. Using CNT as the substrate ensured the self-supporting nature of the electrode. Consequently, the (Ni_0.5Co_0.5)₃V₂O₈/NGQD@CNT composite exhibits an ultra-high specific capacitance of 3018.2 F g^-1 at 1 A g^-1 and 2332 F g^-1 at 10 A g^-1. The asymmetric supercapacitor constructed with (Ni_0.5Co_0.5)₃V₂O₈/NGQD@CNT and activated carbon (AC) presented an impressive energy density of 160.2 Wh kg^-1 at a power density of 800 W kg^-1. After 8000 charge-discharge cycles, the capacity retention rate was 78.5 %, with a Coulo mbic efficiency consistently above 98 %.