▎ 摘　　要

Graphene material has a large theoretical specific surface area, excellent theoretical conductivity and mechanical flexibility, and is a promising electrode material for supercapacitors. However, two-dimensional graphene sheets are easy to stack, which affects its electrical properties. Specifically, a sponge-like composite hydrogel for high-performance supercapacitors was prepared by one-step hydrothermal method from activated carbon and graphene oxide. Benefiting from the introduced nitrogen-containing groups and the greatly increased specific surface area, the GAC-2 nitrogen-doped activated carbon/graphene hydrogel electrode showed high specific capacitance of 505.6 F g(-1). In addition, the composite hydrogel presented an excellent 3D network structure with abundant internal structural pores, in which graphene and activated carbon were cross-linked by strong covalent bonds. This unique structure greatly improves the mechanical flexibility of the composite electrode (the capacitance retention rate is approximately 87.7% after 500 bending tests). And the self-assembled flexible supercapacitor shows an energy density of 26.9 Wh kg(-1) at 242 W kg(-1) and outstanding capacitance retention rate of about 92.1% after 5000 charge-discharge cycles, confirming its potential application in supercapacitors.