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@NiCo2O4 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.