Hierarchical 3D All-Carbon Composite Structure Modified with N-Doped Graphene Quantum Dots for High-Performance Flexible Supercapacitors.

Flexible supercapacitors have shown enormous potential for portable electronic devices. Herein, hierarchical 3D all-carbon electrode materials are prepared by assembling N-doped graphene quantum dots (N-GQDs) on carbonized MOF materials (cZIF-8) interweaved with carbon nanotubes (CNTs) for flexible all-solid-state supercapacitors. In this ternary electrode, cZIF-8 provides a large accessible surface area, CNTs act as the electrical conductive network, and N-GQDs serve as highly pseudocapactive materials. Due to the synergistic effect and hierarchical assembly of these components, N-GQD@cZIF-8/CNT electrodes exhibit a high specific capacitance of 540 F g-1 at 0.5 A g-1 in a 1 m H2 SO4 electrolyte and excellent cycle stability with 90.9% capacity retention over 8000 cycles. The assembled supercapacitor possesses an energy density of 18.75 Wh kg-1 with a power density of 108.7 W kg-1 . Meanwhile, three supercapacitors connected in series can power light-emitting diodes for 20 min. All-solid-state N-GQD@cZIF-8/CNT flexible supercapacitor exhibits an energy density of 14 Wh kg-1 with a power density of 89.3 W kg-1 , while the capacitance retention after 5000 cycles reaches 82%. This work provides an effective way to construct novel electrode materials with high energy storage density as well as good cycling performance and power density for high-performance energy storage devices via the rational design.