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

 Herein, ferrocene and a nitrogen heterocyclic compound (either melamine or imidazole) were hyper-crosslinked via an external crosslinker through a straightforward Friedel–Crafts reaction, leading to the formation of nitrogen-containing hyper-crosslinked ferrocene polymer precursors (HCPs). These precursors were subsequently carbonized to produce iron–nitrogen-doped porous carbon absorbers (Fe-NPCs). The Fe-NPCs feature a porous structure comprising aggregated nanotubes and nanospheres, with porosity that can be modulated by adjusting the iron and nitrogen content to optimize impedance matching. The use of hyper-crosslinked ferrocenes in constructing porous carbon ensures the uniform distribution of Fe-NxC, N dipoles, and α-Fe within the carbon matrix, providing the absorber with numerous polarization sites and a conductive network. The specially designed Fe-NPC-M2 absorbers exhibit satisfactory electromagnetic wave absorption performance, with 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. This research introduces a novel method for developing highly efficient carbon-based absorbing agents by utilizing hyper-crosslinked polymers as precursors.