Hollow double-shell structured Void@SiO2@Co-C composite for broadband electromagnetic wave absorption

Current electromagnetic wave (EMW) absorbing materials generally face the problem of narrow absorption bandwidth, which is the bottleneck in practical applications. Exploring new strategies and designing new architectures to overcome this problem is urgent but challenging. Here, a hollow double-shell structured magneto-electric composite, composed of an internal hollow cavity, a middle SiO2 matching shell and an outer Co-C porous shell ([email protected]2@Co-C), was prepared by assembling metal–organic-framework particles on hollow SiO2 cavity and pyrolysis. The multiple magnetic resonances, magneto-electric interface polarization, defect dipole polarization and conductivity of the composite can be well tuned by controlling the pyrolysis temperature. In particular, the hollow SiO2 cavity plays an essential role in improving impedance matching. Benefitting from the synergistic effect between hollow SiO2 cavity, porous carbon shell and Co particles, the [email protected]2@Co-C composite exhibits a broad effective absorption bandwidth above 7 GHz at a thin thickness of 2.2 mm, which is superior to other Co-C composites (less than 6 GHz). This work provides an effective solution for broadening the EMW absorption bandwidth.