Preparation of Porous Fe–N–C Composite from Cotton Straw and Its Supercapacitor Performance

The doping of multiple heteroatoms can improve the electrochemical properties of carbon substrates. However, in existing studies, carbon, iron and nitrogen sources are generally mixed directly and then pyrolyzed for secondary activation. This tends to form aggregates of metal particles or metal oxides and requires the consumption of large amounts of alkali and energy. Therefore, there is an urgent need to develop an environmentally friendly technology capable of uniformly doping iron and nitrogen into carbon materials. In this work, porous Fe–N–C composites were prepared at 600 °C using potassium humate (HA-K) obtained from cotton straw by low-temperature pyrolysis as the carbon source, and urea-iron complexes formed by the pre-coordination of urea and Fe as the iron and nitrogen sources. In the absence of secondary activation, the best sample Fe-NHPC-2 had a good mesoporous structure with high specific surface area (889. 01 m 2 g −1 ). It had a high specific capacitance of 256.8 F g −1 at a current density of 0.5 A g −1 . The capacitance retention was 92.6% after 10,000 cycles at a current density of 10 A g −1 . In the symmetric supercapacitor application, the energy density reached 33.16 Wh kg −1 when the power density was 600.2 W kg −1 .