Large-Scale Nanofiber Manufacturing| Design and synthesis of non-homogeneousCoSz/carbon composite nanofibers forenhanced microwave absorption

Associate Professor Huo Yashan & Professor He Zhihui (Yan'an University) 《Carbon》: Design and Synthesis of Non-Homogeneous CoS2/Carbon Composite Nanofibers for Enhanced Microwave Absorption

With increasing reliance on electronic devices, electromagnetic radiation has surged, affecting device performance, human health, and information security. Additionally, advancing radar detection demands better electromagnetic stealth for next-gen military equipment. Thus, effective electromagnetic wave absorption/shielding has become critical in materials science and electromagnetic compatibility.

Recently, Associate Professor Huo Yashan and Professor He Zhihui (Yan'an University) published research in Carbon titled *"Design and synthesis of non-homogeneous CoS2/carbon composite nanofibers for enhanced microwave absorption."* The team embedded CoS2 nanoparticles into porous carbon fibers via electrospinning and pyrolysis, creating heterogeneous CoS2/carbon nanofibers with exceptional microwave absorption: minimum reflection loss of −59.84 dB at 11.1 GHz and 4.9 GHz effective bandwidth.

In addition, the research team conducted theoretical calculations to analyze the electronic structure and dielectric properties of the material, revealing the polarization and conduction loss mechanisms responsible for microwave attenuation. Radar cross-section (RCS) simulations further demonstrated that CoS2/carbon composite nanofibers can significantly reduce strong electromagnetic scattering from metal backplanes, showcasing their potential for evading radar wave detection. By investigating impedance matching and electromagnetic attenuation mechanisms, valuable insights were provided for developing advanced microwave absorbers.

Figure 1: Preparation and micro-morphology of CoS2/C composite nanofibers.

Figure 1(a) illustrates the synthesis process of CoS2/C composite nanofibers. PAN-based fibers obtained through electrospinning were first carbonized to form graphitic Co/C nanocomposite fibers, followed by sulfidation to convert Co into CoS2, yielding CoS2/C composite nanofibers. Figures 1(b-e) show SEM images of PAN-based nanofibers with different cobalt salt concentrations, while Figures 1(f-i) provide magnified views. The nanofibers exhibit smooth surfaces and uniform diameters of approximately 350 nm, with minimal influence on fiber size from cobalt salt addition. Post-carbonization and sulfidation images (Figures 1(j-q)) reveal nanoparticles with diameters of 70-90 nm embedded on the nanofiber surfaces, while the nanofiber diameter decreases to 300 nm. During carbonization, PAN nanofibers transform into carbon, and Co3+ ions are reduced to metallic Co. Due to surface energy effects, smaller cobalt nanoparticles aggregate to form larger ones. After sulfidation, the fiber morphology is preserved (Figures 1(j-m)), forming a 3D network structure that enhances conductivity and attenuation through amplified scattering effects.

Figure 2: 3D reflection loss and 2D mapping of CoS2/C composite nanofibers.

The microwave absorption performance was evaluated by plotting reflection loss (RL) curves (Figures 2(a-d)). CoS2/C-3 demonstrates excellent minimum reflection loss of -59.84 dB at 11.1 GHz with a matching thickness of 2.5 mm. Notably, the effective absorption bandwidth of CoS2/C-3 nearly covers the entire X-band, highlighting its promising application potential. The synergistic effects of multiple scattering, conduction loss, defect polarization, interface polarization, and dipole polarization endow CoS2/C-3 composite nanofibers with strong absorption, broad bandwidth, low loading, and relatively thin matching thickness, making them promising candidates for high-performance microwave absorption materials.

Figure 3: (a) Theoretical model of CoS2/C-3; (b) Charge density difference map; (c) Theoretical simulated dielectric constants of CoS2/C-3 and CoS2; (d) Reflection spectrum; (e) Loss function.

First-principles calculations analyzed the dielectric properties of CoS2/C, revealing stable energy states and confirming its magnetic characteristics. The study shows that electron transfer from CoS2 to carbon fibers enhances the composite's conductivity and optimizes microwave absorption performance. The CoS2/C composite exhibits strong dielectric polarization effects, increasing dielectric loss and thereby improving microwave absorption capability. Compared to pure CoS2, CoS2/C shows significantly higher real and imaginary parts of dielectric constant, indicating stronger polarization capability and loss characteristics. CoS2/C demonstrates broader absorption range and lower reflection coefficient, further enhancing microwave loss performance.

Figure 4: RCS simulation results of prepared CoS2/C composite nanofibers.

Additionally, radar cross-section (RCS) simulations of CoS2/C composite nanofibers using electromagnetic and multiphysics simulation software show that lower RCS values indicate better microwave absorption performance. Compared to other absorbing materials, CoS2/C-3 maintains the lowest RCS values (below -10 dBm²) within the -90° to 90° range and shows the most significant RCS reduction (23.1 dBm²), demonstrating its excellent electromagnetic wave absorption capability. This study confirms the potential feasibility of the 3D network structure of CoS2/C composite nanofibers for high-frequency stealth applications in both civilian and military fields.