Controllable adjustment of cavity of core-shelled Co₃O₄@NiCo₂O₄ composites via facile etching and deposition for electromagnetic wave absorption

Core-shell structural cobalt- and nickel-based metal oxides with different compositions have rarely been reported as electromagnetic wave absorption materials. Herein, core–shell structural Co₃O₄@NiCo₂O ₄ composites have been successfully fabricated via simple etching and deposition reaction of Co-based metal–organic framework with subsequent calcination in air. According to morphological evolution, it is verified that the cavity volume between Co₃O₄ core and NiCo₂O₄ shell could be modulated effectively by simply controlling proton etching and deposition reaction. The electromagnetic wave absorption properties of the Co₃O₄@NiCo₂O₄ composites were investigate. It was demonstrated that multiple interfacial polarization of heterogeneous interfaces involving cavities, such as Co₃O₄/Void, Void/NiCo₂O₄ and Co₃O₄/NiCo₂O₄ have made great contribution to the excellent electromagnetic wave absorption performance. Co₃O₄@NiCo₂O₄ with optimized microstructure exhibited RL value as strong as −34.42 dB with a broad effective absorption bandwidth up to 4.88 GHz at a layer thickness of 2.6 mm. It is believed that core–shell structural cobalt- and nickel-based metal oxides will become an excellent candidate for high-performance electromagnetic wave absorber.