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

Abstract

To improve electromagnetic (EM) wave attenuation and its absorption properties, herein, for the first time, we grow needle-like magnetic NiCo2O4 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 NiCo2O4 coating and interfacial polarization.

Dense NiCo2O4 Nanoneedles Grown on Carbon Foam Showing Excellent Electrochemical and Microwave Absorption Properties

“…[26] The bands at 1509 cm À 1 , 1376 cm À 1 , and 3339 cm À 1 indicate the presence of HÀ OÀ H bending vibration mode. [27] The two bands at 747 cm À 1 and 827 cm À 1 can be attributed to metal-oxygen of CoÀ O and NiÀ O stretching vibrations and the formation of spinel NiCo 2 O 4 structure. [28] Significant blue-shift of NiÀ O indicates a strong bond, perhaps a hydrogen bonding, between the CF and NiCo 2 O 4 particles, wherein the carbonyl group of CF and the NiÀ O groups of NiCo 2 O 4 are involved.…”

Improved Microwave Absorption Performance with Sustainable Porous Carbon/Carbon Nanotube Composites

“…Therefore, we can rule out a contribution from magnetic losses. Dielectric loss is related to interfacial polarization, defect-induced polarization, dipole/molecular polarization, electronic polarization, ionic polarization, and atomic polarization 65,66 . Ionic, atomic, and electronic polarization are not present in the 2-18 GHz range.…”

“…By increasing ε", the alternate current (AC) conductive increases further enhancing conductive loss. The ionic and electronic polarization occurs in the ultraviolet or infrared region 65,66 . The dielectric loss behavior can be explained by the Debye theory.…”

NiCo2O4 Nanoneedle-Coated 3D Reticulated Vitreous Porous Carbon Foam for High-Performance All-Solid-State Supercapacitors

“…The resulting nanoneedle "forest" was found to be strongly bonded to the carbon substrate. 28 A strong bond of active material with the substrate is paramount for the long-term electrochemical performance of the electrode. 29 This strategy would effectively provide and utilize the active material's surface area, and more importantly, it is binder-free.…”

“…Previously, we have shown that NiCo 2 O 4 grown on RVC foam significantly improved the EMI shielding and microwave absorption properties of the RVC foam. 28 However, this newly developed material's electrochemical properties and energy storage capability are still unknown.…”