In situ preparation of Co3O4/CF flexible composites with core-shell structure as high-performance microwave absorbers

This study obtained cobalt nitrate (Co3O4)/carbon fibers (CF) composites with a core-shell structure using in situ Co3O4 growth on lightweight and flexible hydrophilic CF through a hydrothermal synthesis method and simple heat treatment to improve the attenuation of microwaves and their absorption properties. The urea content was adjusted to tune the needle-like morphology of Co3O4. The results showed that sample S3 had excellent microwave absorption (MA) performance with a minimum reflection loss (RLmin) of −61.55 dB at a thickness of 4.75 mm. However, the thickness corresponding to the maximum effective absorption bandwidth (EAB, RL<-10 dB) of 4.72 GHz was only 1.88 mm, covering almost the entire Ku band. CF, as the core of structures, significantly impact microwave reflection. However, the Co3O4 shell coating dominated the dielectric loss of the Co3O4/CF composite, and its MA performance improved with the refinement of the Co3O4 structures. This study provided a practical solution for preparing lightweight and efficient transition metal oxide and carbon-based MA composites.