Hollow hydrangea-like nitrogen-doped NiO/Ni/carbon composites as lightweight and highly efficient electromagnetic wave absorbers

Hierarchical hollow-structured magnetic–dielectric materials are considered to be promising and competitive functional absorbers for microwave absorption (MA). Herein, a hierarchical hollow hydrangea multicomponent metal oxides/metal-carbon was designed and successfully produced via a facile self-assembly method and calcination process. Adequate magnetic NiO and Ni nanoparticles were suspended within the hollow hydrangea-like nitrogen-doped carbon matrix (HH N-NiO/Ni/C), constructing a unique hierarchical hollow structured multicomponent magnetic–dielectric MA composite. The annealing temperature and oxidation time were carefully regulated to investigate the complex permittivity and permeability. HH N-NiO/Ni/C delivers exceptional MA properties with maximum reflection loss of –45.8 dB at 1.7 mm thickness and displays a wide effective absorption frequency range of 5.6 GHz. The superior MA performance can be attributed to the following aspects: (1) The hierarchical hollow multicomponent structure offers plentiful of heterojunction interfaces triggering interfacial polarization; (2) nitrogen doped-carbon (N-C) facilitates the conductive loss by the unique electron migration path in the graphitized C and NiO/Ni; (3) magnetic NiO/Ni nanoparticles homogeneously dispersed within N-C form extensive C skeleton and strengthen the magnetic response ability; (4) hierarchical hollow wrinkled structures possess a large interspace and heterogeneous interface improving polarization loss and enhancing multireflection process and the unique structure satisfies magnetic and dielectric loss simultaneously resulting from synergistic effects of different components within the composites.