This work demonstrates that Ni/C microspheres with a desirable yolk–shell structure are potential candidates for the application in microwave absorption field. Such excellent microwave absorption performance can be attributed to the synergistic effect of the magnetic and dielectric losses of Ni/C microspheres due to natural resonance, dipolar polarization and multiple interfacial polarizations at a unique yolk–shell interface, achieving the optimization of impedance matching and microwave attenuation. The integrated bandwidth can achieve 12.3 GHz covering Ku-band (12–18 GHz), X-band (8–12 GHz), and most of C-band (5.7–8 GHz) with an appropriate thickness of 1.4–3.9 mm. The yolk–shell Ni/C microspheres obtained at 600 ☌ exhibited the optimal reflection loss (RL) reaching −39 dB with a bandwidth of 3.8 GHz (RL < −10 dB) at a thin matching thickness of 1.8 mm. Meanwhile, the attenuation coefficient of Ni/C microspheres increased with the increment in pyrolysis temperature. The degree of crystallization of Ni and C was improved by increasing the pyrolysis temperature, which resulted in enhanced complex permittivity and optimized impedance matching of Ni/C microspheres for damping microwave.
The Ni-MOF with a yolk–shell structure was prepared by a solvothermal method with an appropriate molar ratio of Ni(NO3)2♶H2O to C9H6O6 in the presence of PVP. Yolk–shell Ni/C microspheres composed of core–shell nanoparticles were successfully fabricated by decomposing a Ni-based metal–organic framework (Ni-MOF) at 500 ☌ and 600 ☌.
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