Sandwich-like sulfur-free expanded graphite/CoNi hybrids and their synergistic enhancement of microwave absorption

Sulfur-free expanded graphite (EG) was prepared by chemical oxidation, then EG-based cobalt-nickel alloy hybrid (EG@CoNi) was obtained via hydrothermal method in this work. CoNi particles with the diameter of 0.1–0.5 µm were tightly attached to the surface of the layered EG. The incorporation of CoNi was conducive to the absorption of electromagnetic waves due to the increase in Ms and Hc, which enhanced the soft magnetization of EG@CoNi hybrids. The resulting EG@CoNi hybrids exhibited better dielectric loss than CoNi particles, and the optimal value of reflection loss (RL) reached − 50 dB, while the optimal bandwidth less than − 10 dB was 4 GHz, indicating enhanced microwave absorption characteristics. The well impedance matching and electromagnetic wave attenuation of EG@CoNi hybrids benefited from the synergy and double-loss mechanism between CoNi nanoparticles and EG. The dielectric loss in the double-loss mechanism was mainly dipole polarization and interface polarization, while the magnetic loss was mainly the natural ferromagnetic resonance and eddy current loss of CoNi nanoparticles. These multi-layer EG@CoNi hybrids with light weight and high dielectric characteristics would show good application prospects in high-efficiency electromagnetic wave absorbers.