Hollow Co/NC@MnO₂ polyhedrons with enhanced synergistic effect for high-efficiency microwave absorption

High-efficiency microwave absorbents with lightweight characteristics possess prospective applications in electromagnetic radiation protection, but still face huge challenges. Herein, hollow Co/NC@MnO₂ (H–Co/NC@MnO₂) polyhedrons with hierarchical structure and enhanced synergistic effect are successfully fabricated via the collaborative steps of etching-pyrolysis-hydrothermal reaction. Specifically, hollow engineering of Co/NC with heteroatoms endow the polyhedrons with lightweight characteristics, dipolar polarization and magnetic loss, hierarchical MnO₂ nanosheets with oxygen vacancies grant dielectric loss and multiple scattering, and the dielectric-magnetic synergistic effect between Co/NC and MnO₂ promote impedance matching and strengthen interfacial polarization. Benefiting from the above mentioned advantages, the H–Co/NC@MnO₂ polyhedrons exhibit high-efficiency microwave attenuation at a low filler loading of 20 wt%. The optimal reflection loss reaches −54.7 dB and the effective absorption bandwidth ranges from 11.8 GHz to 18 GHz (6.2 GHz) with a thickness of only 2.1 mm. These findings provide us a promising strategy in developing high-efficiency and lightweight microwave absorbents for practical applications.