Tuning nitrogen doping types and pore structures in carbon nanosheets as electrodes for supercapacitor by controlling existence form of iron species

Nitrogen-doped hierarchically porous carbon (HPC) with plate-like intertwined nanosheets structures and different distributed pores is fabricated by directly carbonize phenyl polyimide nanosheets with FeCl 3 •6H 2 O as activator and regulator. Inspiringly, the nitrogen doping types, morphologies, pore structures and nitrogen content of HPC can regulate by controlling the existence form of Fe species in HPC under different carbonization temperature. The optimal HPC sample possesses the uniform distributed pores, the high N content (7.8 wt%) and the appropriate specific surface area. Especially, the optimal HPC shows satisfactory specific capacitance of 254 F g −1 at the current density of 0.5 A g −1 in 2 M KOH electrolyte. Moreover, when it comes to both positive and negative electrode materials for two-electrode symmetric cell, the operating voltage window of the symmetric cell can extend up to 1.8 V and provide an energy density of 14.4 W h kg −1 at power density of 225 W kg −1 , as well as an excellent cycling stability of 93% capacitance retention after 15 000 cycles in 0.5 M Na 2 SO 4 electrolyte.