In Situ Coating of Needle-like NiCo₂O₄ Magnetic Nanoparticles on Lightweight Reticulated Vitreous Carbon Foam toward Achieving Improved Electromagnetic Wave Absorption

To improve electromagnetic (EM) wave attenuation and its absorption properties, herein, for the first time, we grow needle-like magnetic NiCo 2 O 4 nanoparticles in situ on lightweight open cell reticulated vitreous carbon (RVC) foam by the hydrothermal method, leading to hierarchically nanostructured foam. The foam was synthesized by the carbonization of flexible polyurethane foam followed by acid treatment. The coating structure, stability, and performance were systematically investigated by various complementary techniques using XRD, XPS, Raman, and FTIR spectroscopies, compression test, and ultrasonication. The foam coated for 12 h exhibited considerably improved shielding effectiveness (SE), i.e., ∼36 dB from ∼23 dB for the bare RVC foam in the X-band, leading to ∼99.97% shielding efficiency. Although the foams mainly showed reflection-dominated properties regardless of the coating, the EM absorption improved with coating. The shielding mechanism is explained by means of reflection and absorption coefficients and dielectric and magnetic losses manifested by NiCo 2 O 4 coating and interfacial polarization.