Iron–nitrogen-doped porous carbon absorbers constructed from hypercrosslinked ferrocene polymers for efficient electromagnetic wave absorption

Herein, an external crosslinker facilitated the hypercrosslinking of ferrocene and a nitrogen heterocyclic compound (either melamine or imidazole) through a direct Friedel–Crafts reaction, which led to the formation of nitrogen-containing hypercrosslinked ferrocene polymer precursors (HCP-FCs). Subsequent carbonization of these precursors results in the production of iron–nitrogen-doped porous carbon absorbers (Fe–NPCs). The Fe–NPCs demonstrate a porous structure comprising aggregated nanotubes and nanospheres. The porosity of this structure can be modulated by adjusting the iron and nitrogen contents to optimize impedance matching. The uniform distribution of Fe–N_xC, N dipoles, and α-Fe within the carbon matrix can be ensured by using hypercrosslinked ferrocenes in constructing porous carbon, providing the absorber with numerous polarization sites and a conductive network. The electromagnetic wave absorption performance of the specially designed Fe–NPC-M₂ absorbers is satisfactory, revealing a minimum reflection loss of −55.3 dB at 2.5 mm and an effective absorption bandwidth of 6.00 GHz at 2.0 mm. By utilizing hypercrosslinked polymers (HCPs) as precursors, a novel method for developing highly efficient carbon-based absorbing agents is introduced in this research.