Multifunctional hierarchical BN/MXene-Fe₃O₄ aerogel for efficient thermal management and ultra-broadband microwave absorption

A novel heat-insulating and microwave-absorbing aerogel has been constructed by directional freeze-drying and melt-welding, which realizes strong heat insulation (the thermal insulation layer) and ultra-broadband electromagnetic (EM) wave-absorption properties (EM wave absorption layer). The oriented structure formed by directional freeze-drying endows the thermal insulation layer with anisotropy, which greatly reduces longitudinal heat conductivity. As a result, effective thermal insulation can be realized in a thickness as low as 3 mm. As for EM wave absorption layer, the synergistic effect of the porous aerogel structure, alongside excellent impedance matching and attenuation ability of the multilayer material enables a wider effective absorption bandwidth (EAB) and lower peak reflection loss (RL). In addition, this work integrates the thermal insulation layer and EM-wave absorption layer into a hemispherical bionic moth-eye unit structure. The construction of hemispherical cell structures further improves impedance matching, which realizes the absorption of the full band of EM waves from 2 to 18 GHz within a high-temperature environment, while maintaining an EAB of more than 6.4 GHz even at an incidence angle of 60°. This work not only realizes the integration of ultra-strong thermal insulation and ultra-broadband wave absorption, but also provides guidelines for the construction of multilayer aerogels and ultra-broadband metamaterials, which addressing the need for EM protection in harsh environments.