Synthesis of novel hierarchical CoNi@NC hollow microspheres with enhanced microwave absorption performance

The rational design on the morphology and microstructure of magnetic carbon-based composites can enhance microwave absorption performance. Herein, a novel hierarchical CoNi@NC hollow microspheres have been successfully synthesized, involving the fabrication of hierarchical CoNi-based carbonate hydroxide hollow microspheres self-assembled by nanosheets using CoNi-glycerate microspheres as self-template, the uniform coating of a layer of polydopamine (PDA) on the surface, and the calcination process at different temperatures. Importantly, the calcination temperature can significantly influence the morphology, microstructures, and microwave absorption performance. All CoNi-based carbonate hydroxide nanosheets coated with PDA can be successfully converted into abundant small CoNi nanoparticles embedded into carbon layer without the agglomeration of CoNi alloys when the calcination temperature is 700 °C. The CoNi@NC-700 sample exhibits outstanding microwave absorption ability especially in X band thanks to optimized impedance matching and enhanced attenuation ability. The RLmin can reach − 69.58 dB at 10.09 GHz with a matching thickness of 2.99 mm, and the effective absorption bandwidth (EAB) is 4.5 GHz (7.97–12.47 GHz) at 3.08 mm, covering the whole X band. Moreover, the broadest EAB is 5.3 GHz (12.7–18 GHz) at 2.13 mm. We believe that this research will provide a new thought to enhance the microwave absorption capability.