Nitrogen-Doped Hierarchical Porous Carbon from Wheat Straw for Supercapacitors

In this paper, wheat straw was converted into nitrogen-doped hierarchical porous carbon (N-HC) by direct pyrolysis of wheat straw with CaCl2 as an activator and melamine as a nitrogen resource. The as-prepared samples exhibit different hierarchical porous structures and nitrogen contents in a temperature range from 600 to 800 °C. Compared with other samples, the N-HC-800 displays a large amount of micropores, uniform mesopores, a high specific surface area (892 m2 g–1), and moderate nitrogen doping (5.63 wt %). Therefore, the N-HC-800-based supercapacitor exhibits a high specific capacitance of 275 F g–1 at a current density of 0.2 A g–1, a high capacitance retention ratio of 81% even at 8 A g–1, and an excellent cycling stability (over 97% retention rate after 10 000 cycles) in 6 M KOH solution. This work not only proposes a novel routine for the development of porous carbon materials for supercapacitor but also provides a new option for the processing of waste wheat straw instead of being burned in rural areas.