Hierarchical NiCo₂O₄/Co₃O₄/NiO porous composite: a lightweight electromagnetic wave absorber with tunable absorbing performance

Hierarchical NiCo₂O₄/Co₃O₄/NiO composite was fabricated through a facile hydrothermal method, followed by a post-annealing treatment. The obtained ternary composite, with a flower-like morphology, consists of radially assembled porous nanosheets. Benefiting from the unique structure and the synergistic effect among multiple components, the NiCo₂O₄/Co₃O₄/NiO composite exhibited strong electromagnetic wave (EMW) absorption in both low-frequency and high-frequency regions by simply changing its filler loading in the matrix. The absorber with a filler loading of 30 wt% possessed a reflection loss of −28.6 dB at a small layer thickness of 1.64 mm in the K_u band, while the absorber with less filler loading at 20 wt% achieved a reflection loss of −57.0 dB in the C band. The light weight, small thickness, strong and tunable absorbing property of the NiCo₂O₄/Co₃O₄/NiO composite make it attractive for developing a high-performance electromagnetic wave absorber.