Air-induced dual-cavity yolk–shell architecture in lightweight hollow Fe3O4@air@Co/C nanocomposites enabling high-efficiency electromagnetic wave absorption

The rational design of yolk–shell structured materials with integrated dielectric–magnetic synergy has emerged as a critical strategy for developing lightweight and high-performance electromagnetic wave (EMW) absorbers. Comparing to the conventional yolk–shell structures that typically rely on single cavity configuration, the air-induced dual-cavity yolk–shell structures offer both lightweight absorber design and substantial enhancements in interfacial polarization over wide frequency range. To this end, this study proposes a novel “coating-protected etching-high temperature carbonization” strategy to successfully construct an air-induced dual-cavity yolk–shell hollow Fe₃O₄@air@Co/C composite absorber. The unique nanostructure possesses two independent cavities: one within the inner hollow Fe₃O₄ core, and another between the inner Fe₃O₄ core and the Co/C shell. The dual cavities not only significantly reduce the material density but also optimize the impedance matching. Importantly, the synergistic effects of the air-induced dual-cavity interfaces (Fe₃O₄-air and Co/C-air) amplify multi-interfacial polarization and improve the absorption ability via combined magnetic and dielectric loss mechanisms. Experimental results demonstrate that the optimized absorber achieves a remarkable reflection loss of –67.21 dB and a maximum effective absorption bandwidth (EAB) of 5.12 GHz (12.08–17.20 GHz) at an ultra-thin thickness of 2.0 mm and a low filler loading of 20 wt%. Collectively, our findings provide a new design approach for constructing high-efficiency, lightweight EMW absorption materials.