Hollow engineering of sandwich NC@Co/NC@MnO₂ composites toward strong wideband electromagnetic wave attenuation

Multiple hetero-interfaces would strengthen interfacial polarization and boost electromagnetic wave absorption, but still remain the formidable challenges in decreasing filler loadings. Herein, sandwich NC@Co/NC@MnO₂ composites with hollow cavity, multiple hetero-interfaces, and hierarchical structures have been fabricated via the cooperative processes of self-sacrifice strategy and sequential hydrothermal reaction. In the sandwich composites, middle magnetic components (Co/NC) are wrapped by inner N-doped carbon (NC) matrix and outer hierarchical MnO₂ nanosheets. Importantly, hollow engineering of sandwich composites with multiple hetero-interfaces greatly facilitates the enhancement of absorption bandwidth without sacrificing the absorption intensity. The maximum reflection loss of sandwich NC@Co/NC@MnO₂ composites reaches -44.8 dB at 2.5 mm and the effective bandwidths is achieved as wide as 9.6 GHz at 2.3 mm. These results provide us a new insight into preparing efficient electromagnetic wave absorbers by interface engineering and hollow construction.