Sandwich-like nitrogen-doped porous carbon/graphene nanoflakes with high-rate capacitive performance.

Sandwich-like nitrogen-doped porous carbon/graphene nanoflakes (NPCFs) are prepared via a two-step approach, firstly by using in situ polymerization of pyrrole (Py) on the surface of graphene oxide (GO) and then by KOH activation under an Ar atmosphere. As the shape-directing agent and conductive matrix, graphene sheets play an important role in enhancing NPCFs' electrochemical performance. The NPCFs exhibit high specific surface area (2502 m(2) g(-1)), short ion diffusion path (ca. 30 nm), high conductivity (72 S m(-1)) and a considerable nitrogen level (6.3 wt%). These intriguing features render NPCFs a promising electrode material for electrochemical supercapacitors, which displays high specific capacitance (341 F g(-1)), excellent rate capability (over 71% retention ratio at 50 A g(-1)) and outstanding cycling stability (almost no capacitance loss after 2000 cycles) in a 30 wt% KOH aqueous electrolyte. Besides, the assembled symmetrical supercapacitor delivers a high gravimetric energy density of 11.3 Wh kg(-1) in an aqueous electrolyte and 66.4 Wh kg(-1) in an organic electrolyte.