In Situ Encapsulation of Iron Complex Nanoparticles into Biomass‐Derived Heteroatom‐Enriched Carbon Nanotubes for High‐Performance Supercapacitors

The capacitive performance of carbon materials could be enhanced by means of increasing the number of active sites, the surface area, and the porosity as well as through incorporating heteroatoms into the carbon framework. However, the charge storage through electric double‐layer mechanism results in limited increase in capacitance of modified carbon materials. Herein, a simple and straightforward strategy is introduced for in situ synthesizing iron complex (FeX, which X includes O, C, and P) nanoparticles encapsulated into biomass‐derived N, P‐codoped carbon nanotubes (NPCNTs), using a natural resource, egg yolk, as heteroatom‐enriched carbon sources and potassium ferricyanide as the precursor for iron complex. Compared with heteroatom‐enriched carbon nanomaterials derived from the carbonization of egg yolk, the synergetic function of the heteroatom doping, the incorporation of FeX nanoparticles, and the unique structural characteristics endows the as‐prepared sample with largely improved electrochemical performance. As expected, FeX@NPCNTs hybrid nanomaterials exhibit superior capacitive performance, including high specific capacitance, impressive rate performance, and excellent cycle stability. Using the as‐prepared FeX@NPCNTs hybrid nanomaterials as electroactive materials, a symmetric supercapacitor with high capacity and a long‐term cyclability is finally demonstrated (more than 99% capacitance retention after 50 000 cycles at a current density of 10 A g −1 ).