▎ 摘　　要

A nitrogen-doped porous carbon nanosheet/graphene composite (NPCN/G) with layer-by-layer structure is facilely synthesized on a large scale via pyrolysis of a zeolitic imidazolate framework (ZIF-8)/graphene (2D) mixture. The as-prepared NPCN/G owns a high Brunauer-Emmett-Teller (BET) specific surface area (1210 m(2) g(-1)) and nitrogen content (6.1%). The specific capacitance of NPCN/G in 6 M KOH solution reaches 306.4 F g(-1) at a current density of 0.2 A g(-1). Moreover, NPCN/G exhibits an outstanding cycle stability with 97.4% capacitance preservation after 3500 cycles at a current density of 5 A g(-1). Compared to the nitrogen-doped porous carbon nanosheets (NPCN), NPCN/G shows a higher capacitance and a superior cycle stability which can be ascribed to the synergistic effect between the GO nanosheets and carbon nanosheets. In addition, the specific capacitance of NPCN/G enhances with increasing concentration of electrolyte.