Quasi solid-state supercapacitors using graphene quantum dots modified activated carbons as electrode materials

Quasi-solid-state supercapacitors with high energy density and flexibility are critical for next-generation energy storage. Herein, we report a rational design of activated carbon (AC) electrodes modified with boron-/fluorine-codoped graphene quantum dots (B-/F-GQDs), integrated with a poly(vinylidene fluoride-co-hexafluoropropylene)/tetraethylammonium tetrafluoroborate (PVDF-HFP/TEABF₄) gel polymer electrolyte. The uniformly distributed GQDs introduce heteroatom functional groups and nanoscale protrusions, enhancing surface polarity and electrolyte wettability while optimizing the mesopore architecture. Consequently, the AC-GQD electrodes exhibit synergistic electric double-layer and pseudocapacitive behaviors, enabling accelerated ion diffusion and reduced internal resistance. The resulting quasi-solid-state device delivers a competitive specific capacitance of 59.7 F g^-1 for a single electrode, corresponding to a cell energy density of 14.5 Wh kg^-1, and excellent rate performance. Furthermore, the device demonstrates outstanding cycling stability (over 2000 cycles with >99.5% coulombic efficiency) and practical viability in a flexible pouch-type configuration. This work provides an effective strategy for engineering carbon electrode interfaces for advanced quasi-solid-state energy storage.