Template-free synthesis of nitrogen-doped hierarchical porous carbon for supercapacitor electrodes

We report a novel and template-free method to fabricate the nitrogen-doped hierarchical porous carbon (HPC) from porous copolymer microsphere of vinylidene chloride-acrylonitrile (VDC-AN). Porous copolymer microsphere of VDC-AN was synthesized by the suspension copolymerization of vinylidene chloride (VDC), acrylonitrile (AN) in the presence of a pentane blowing agent. The as-prepared HPC possessed nitrogen-doped hierarchical porous structure with high BET surface area (1560 m(2)/g) and a large pore volume (0.76 cm(3)/g). Activated nitrogen-doped hierarchical porous carbon (A-HPC) materials were prepared by subsequent surface activation with KOH solution. The effects of activation temperature on the pore structure and supercapacitive behavior were systematically studied. The result showed that the A-HPC had a porous structure with a larger specific surface area (1944 m(2)/g) and higher ratio of mesopore (36.5%) than HPC. Further electrochemical measurements indicated that the A-HPC electrode showed a maximum specific capacitance of 329 F/g at 1 A/g was achieved in 6 M KOH aqueous electrolyte. Meanwhile, it displayed excellent rate capability of 65% capacitance retention as the current density increased from 1 to 20 A/g. It also exhibited good cyclic stability with 90% specific capacitance retained after 3000 cycle tests.