Controllable synthesis of multi-shelled SiO2@C@NiCo2O4 yolk–shell composites for enhancing microwave absorbing properties

Abstract

With the increasingly serious pollution of electromagnetic radiation, the task of developing light and strong wave-absorbing materials is becoming more and more urgent. In this study, a novel SiO₂@C@NiCo₂O₄-1 : 3 composite with a multi-shelled yolk–shell structure was designed and fabricated. NiCo₂O₄ with a lamellar structure grows uniformly on the surface of the C sphere, and there is an obvious cavity between the C shell and the SiO₂ sphere. This unique structure not only improves the impedance matching characteristics of the composite but also produces rich interfaces and increases the dielectric loss. Compared with pure SiO₂@C and NiCo₂O₄, SiO₂@C@NiCo₂O₄ shows stronger microwave absorbing properties, and SiO₂@C@NiCo₂O₄-1 : 3 exhibits the strongest absorption of microwaves only with a loading of 15 wt%. Its minimum reflection loss (RL_min) is −46.96 dB, and the effective absorption band (EAB, RL <−10 dB) is 3.76 GHz. These results reveal that the multi-shelled SiO₂@C@NiCo₂O₄-1 : 3 composites are promising microwave absorbers.