▎ 摘　　要

In this work, a lignosulfonate has been used for synthesizing the graphene quantum dots (GQDs) with many functional groups by a two-step method. Then a graphene-based composite hydrogel (GH-GQD) was obtained through the modification of the functionalized GQDs. Results showed that the composite hydrogel had a highly porous structure and numerous active sites. Accordingly, the assembled GH-GQD electrode exhibited an impressive specific capacitance of 451.7 F g(-1) at a current density of 0.5 A g(-1), a good cycle stability (89.0% capacitance retention after 10000 charge/discharge cycles) and mechanical flexibility (93.3% capacitance retention bent to 180 degrees). The present findings indicate a great potential of the graphene hydrogels modified with the functionalized GQDs in fabricating flexible supercapacitor electrodes.