Constructing yolk-shell Co@void@PPy nanocomposites with tunable dielectric properties toward efficient microwave absorption

The cobalt-based absorbing materials with core-shell structure have been widely investigated and developed in the microwave absorption territory, but their shortcomings such as relatively high density and weak dielectric loss limit their practical applications. In this work, taking the modification of microstructure and coating material as the cut-in point, we fabricated the Co@void@polypyrrole (PPy) nanocomposites (NCs) with yolk-shell structure and conductive polymer PPy coating via an integration of hydrogen plasma-metal reaction (HPMR), in-situ SiO₂/PPy coating and SiO₂-etching approaches. The Co@void@PPy with a PPy layer thickness of 7.6 nm exhibits the optimal microwave absorption performance. The minimum reflection loss (RL) value comes up to −28.4 dB at 1.4 mm, and the corresponding effective absorption bandwidth (EAB, RL≤ −10 dB) is 5.7 GHz. The optimal EAB is 7.2 GHz with a thickness of only 1.6 mm, where the RL_min is −23.4 dB. Such excellent dielectric loss property and attenuation ability is closely related to the PPy coating and the yolk-shell structure, which give rise to abundant interfaces between PPy and Co core and greatly promote multiple scattering and interface polarization. Accordingly, the yolk-shell structured Co@void@PPy NCs can be a competent candidate in the region of high-performance absorbers.