▎ 摘　　要

In this paper, a porous free-standing nitrogen-doped graphene (NG) film for high energy density supercapacitor is prepared via a facile hydrogel strategy. Taking advantage of the hydrogel behavior together with the mechanical stability of GO sheets, an interconnected macro-porous nitrogen-doped free-standing film is constructed. The nitrogen doping structure ensures sufficient pseudocapacitance and conductivity of the film, while the macro-porous structure favors fast ion adsorption. When assembled in a symmetric two-electrode supercapacitor, not any conductive agent or binder is used. The free-standing NG film shows specific capacitance of 455.4 F g(-1) based on the mass of whole electrode, while no capacitance loss after 5000 cycles. Furthermore, an asymmetric supercapacitor is assembled with this NG film as negative electrode and a macro-porous graphene/polypyrrole composite film synthesized using the similar strategy as positive electrode. An energy density of 34.51 Wh kg(-1) at a power density of 849.77 W kg(-1) is obtained, suggesting great potential of this film for application in energy storage field. (C) 2019 Elsevier Ltd. All rights reserved.