Core-shell FeCo@carbon nanoparticles encapsulated in polydopamine-derived carbon nanocages for efficient microwave absorption

Rational manipulation on chemical composition and microstructure is evolving as a powerful approach to reinforce the electromagnetic (EM) functions of magnetic carbon-based composites. With FeCo Prussian blue analogs (FeCo PBAs) as the nucleation sites, we conduct the polymerization of dopamine (DA) on their surface and then convert the precursor into desirable FeCo alloy/carbon composites. PDA coating is greatly helpful to suppress the microstructure collapse of FeCo PBAs during high-temperature pyrolysis, resulting in a unique hierarchical configuration of core-shell FeCo@C nanoparticles encapsulated in PDA-derived carbon nanocages. The formation of carbon nanocages not only adjusts the relative carbon content, but also affects EM properties of these composites. In particular, the dielectric loss can be significantly enhanced, which further accounts for an improvement in overall attenuation ability toward incident EM waves. When the weight ratio of DA to FeCo PBAs reaches 0.75, the obtained composite will exhibit excellent microwave absorption performance thanks to its decent attenuation ability and matched characteristic impedance. The strongest reflection loss intensity is located at −67.8 dB at 15.8 GHz, and the effective bandwidth covers 11.0–16.3 GHz with the thickness of 2.00 mm. The advantages in microstructure are also established by parallel comparison with a disordered counterpart.