Sub‐Nanometer Fe Clusters Confined in Carbon Nanocages for Boosting Dielectric Polarization and Broadband Electromagnetic Wave Absorption

Abstract Compositing dielectric and magnetic components have been proven effective in optimizing electromagnetic (EM) wave absorption, in which the dielectric loss capacity can be reinforced by the polarization effects of hetero‐substitutions. Here, the dielectric polarization through the energy transformation between the relatively complex permeability and permittivity in nitrogen‐doped carbon nanocages (NCNs) with sub‐nanometer Fe clusters is further boosted. As a transition state between single Fe atoms and Fe 3 O 4 nanoparticles hetero‐substitutions, these subnanometer Fe clusters confined in NCNs can be achieved by carbonizing FePc@ZIF‐8 composites at 900 °C. Benefitting from their unique structures, an enhanced dielectric loss tangent of 1.57 is obtained at 10 GHz, which is 3.0 and 1.6 times higher than those of single Fe atoms and Fe 3 O 4 nanoparticles hetero‐substitutions, respectively. Furthermore, the minimum reflection loss can reach −64.75 dB at 7.1 GHz (2.7 mm) and the effective absorption bandwidth is 6.2 GHz (11.8–18 GHz, covering the full P‐band) at 1.7 mm. The present study provides intrinsic insight into the dielectric polarization behaviors in subnanometer hetero‐substitutions, inspiring the design of high‐performance EM absorption materials.