3D sea urchin like NiCo2O4 and NiCo2O4/MWCNT composites as multifunctional microwave absorbers enabled by interfacial engineering

Abstract

The increasing demand for lightweight and high-efficiency microwave absorbing materials is driven by advancements in wireless communication and radar technologies. In this work, sea urchin-like nickel cobaltite (NiCo₂O₄) and its composite with multiwalled carbon nanotubes (MWCNTs) was synthesized via a scalable hydrothermal method. The hierarchical architecture formed by radially aligned NiCo₂O₄ nanoneedles and entangled MWCNTs creates a robust three-dimensional conductive network that facilitates enhanced dielectric loss, conductivity, and charge transport. Comprehensive structural and spectroscopic analyses confirm the distinctive morphology and the coexistence of redox-active Ni²⁺/Ni³⁺ and Co²⁺/Co³⁺ species, which synergistically contribute to improved electromagnetic wave (EMW) attenuation. The NiCo₂O₄/MWCNT composite achieves a maximum reflection loss of −64.1 dB at 9.1 GHz with a 2 mm thickness, surpassing pristine NiCo₂O₄ with a RL of −48.9 dB. This superior performance is attributed to better impedance matching, conduction loss, and multiple scattering effects, fulfilling the quarter-wavelength condition for destructive interference. A higher attenuation constant (α) further confirms the efficient EMW dissipation. These absorption properties highlight the potential of NiCo₂O₄/MWCNT composites as lightweight, low-cost, environmentally sustainable, and economically viable candidates for advanced microwave absorption applications.