Flexible N-doped carbon fibers decorated with Cu/Cu2O particles for excellent electromagnetic wave absorption

Electrostatic self-assembly sandwich-like 2D/2D NiFe-LDH/MXene heterostructure for strong microwave absorption

MXene has great application potential in electromagnetic (EM) wave absorbers because of its high attenuation ability; however, self-stacking and excessively high conductivity are major obstacles to its widespread use. To address these issues, a NiFe layered double hydroxide (LDH)/ MXene composite with two-dimensional (2D)/2D sandwich-like heterostructure was constructed through electrostatic self-assembly. The NiFe-LDH not only acts as an intercalator to prevent self-stacking of the MXene nanosheets, but also serves as a low-dielectric choke valve to optimize impedance matching. At a thickness of 2 mm and filler loading of 20 wt%, the minimum reflection loss (RL_min) value could reach -58.2 dB, and the absorption mechanism was analyzed based on multiple reflection, dipole/interfacial polarization, impedance matching, and synergy between dielectric and magnetic losses. Furthermore, the simulation of the radar cross section (RCS) further confirmed the efficient absorption properties and application prospects of the present material. Our work demonstrates that designing sandwich structures based on 2D MXene is an effective way to improve the performance of EM wave absorbers.

Regulating conduction and polarization losses by adjusting bonded N in N-doped Cu/CuO/C composites

Conduction and polarization losses are the main forms of dielectric loss, and regulating these mechanisms is key to obtaining favorable electromagnetic wave absorption performance. In this study, the conversion of graphite N and pyridine N in Cu-based metal-organic framework (MOF)-derived composites was adopted to modulate conduction and polarization losses by tuning the pyrolysis temperature and Cu salt concentration. The results show that increasing the pyrolysis temperature facilitates the conversion of pyridine N to graphite N, which is beneficial for conduction loss. Moreover, increasing the Cu concentration promotes the transformation of pyridine N to graphite N as well as, and then promotes the reverse conversion of graphite N to pyridine N, which is conducive to defect-induced polarization. The unique layered Cu/CuO/C composite obtained at 700 °C with a moderate Cu content exhibited the optimal performance with an effective absorption bandwidth of 5.5 GHz (11.6 ∼ 17.1 GHz) at an ultra-thin thickness of 1.56 mm. This is owed to its favorable impedance matching, significant conduction loss, and polarization loss (defect-induced polarization and interfacial polarization). This study provides a novel strategy for regulating conduction and polarization losses.