Three-dimensional nitrogen-doped graphene quantum dots/reduced graphene oxide composite hydrogels as binder-free electrodes for symmetric supercapacitors

Abstract

Herein, nitrogen-doped graphene quantum dots/reduced graphene oxide composite hydrogels (N-GQDs/rGOs) were prepared via a hydrothermal approach from graphene oxide (GO) aqueous solution. During the preparation of the samples, ammonia water was used as reducing agent, pH regulator and nitrogen dopant, and graphene quantum dots (GQDs) were used as spacer between graphene sheets. Benefiting from their three-dimensional porous structures, large specific surface area, large number of heteroatom functional groups (N, O) on the surface, and the synergistic effect between GQDs and graphene sheets, the synthesized samples exhibit excellent electrochemical performance. Particularly, the N-GQDs/rGO-20 sample based binder-free symmetric supercapacitor show a high specific capacitance of 277.8 F g−1 at 0.3 A g−1, and this value can still maintain at 220.9 F g−1 even at 10 A g−1 in 6 M KOH electrolyte. Moreover, the capacitance retention rate of the symmetric supercapacitor can reach 92.7% after 10,000 cycles at 10 A g−1, indicating its excellent cycle stability.