Synthesis of CuCo2S4@Expanded Graphite with crystal/amorphous heterointerface and defects for electromagnetic wave absorption

Abstract

The remarkable advantages of heterointerface and defect engineering and their unique electromagnetic characteristics inject infinite vitality into the design of advanced carbon-matrix electromagnetic wave absorbers. However, understanding the interface and dipole effects based on microscopic and macroscopic perspectives, rather than semi-empirical rules, can facilitate the design of heterointerfaces and defects to adjust the impedance matching and electromagnetic wave absorption of the material, which is currently lacking. Herein, CuCo₂S₄@Expanded Graphite heterostructure with multiple heterointerfaces and cation defects are reported, and the morphology, interfaces and defects of component are regulated by varying the concentration of metal ions. The results show that the 3D flower-honeycomb morphology, the crystal-crystal/amorphous heterointerfaces and the abundant cation defects can effectively adjust the conductive and polarization losses, achieve the impedance matching balance of carbon materials, and improve the absorption of electromagnetic wave. For the sample CEG-6, the effective absorption of Ku band with RL_min of -72.28 dB and effective absorption bandwidth of 4.14 GHz is realized at 1.4 mm, while the filler loading is only 7.0 wt. %. This article reports on the establishment of potential relationship between crystal-crystal/amorphous heterointerfaces, cation defects, and the impedance matching of carbon materials.

Fig. 1. Schematic diagram of preparation and microstructure of CuCo₂S₄@EG heterostructures.

Construction of heterostructures through in-situ growth of defect-rich CuCo₂S₄ on expanded graphite.

Fig. 2. Morphological and compositional characterization of CuCo₂S₄@EG heterostructures.

a Microscopic morphology of CuCo₂S₄@EG. b–d Microscopic morphology and corresponding element distribution of CEG-2, CEG-4 and CEG-6. e Phase composition and content of CEG-2, CEG-4 and CEG-6. f Crystal structure of CuCo₂S₄ and EG. g XPS spectra of CEG-2, CEG-4 and CEG-6, and h S 2p spectra of CEG-2, CEG-4 and CEG-6, the yellow number indicates the S-S ratio.

Fig. 3. Microstructure and atomic coordination information of the CuCo₂S₄@EG.

a, b AC-TEM micrograph of CEG-6. c HAADF-STEM micrograph of CuCo₂S₄. d Distribution diagram of CuCo₂S₄. e HAADF-STEM micrograph of EG. f EPR spectrum of CEG-2, CEG-4 and CEG-6. g Normalized XANES spectra at the Cu K-edge of the Cu foil, CEG-6 and CuO, h FT-EXAFS spectra of the Cu foil, CEG-6 and CuO. i WT of the Cu foil, CEG-6 and CuO. j EXAFS fitting curve for Cu CEG-6 in the k-space. k EXAFS fitting curve for Cu CEG-6 in the R-space. l Vacancy concentration of CEG-2, CEG-4 and CEG-6 samples.

Fig. 4. Electromagnetic wave absorption properties of CuCo₂S₄@EG.

a, b Real part and imaginary part of complex permeability of EG, CEG-2, CEG-4 and CEG-6. c, d Real part and imaginary part of complex permittivity of EG, CEG-2, CEG-4 and CEG-6. e Dielectric loss tangent ($\tan {\delta }_{\epsilon }$) of EG, CEG-2, CEG-4 and CEG-6. f ${\epsilon }_p^{’’}$ of CEG-2, CEG-4 and CEG-6. g, g₁ The charge density difference of heterointerface of CuCo₂S₄@EG. h, h₁ The charge density difference of defect CuCo₂S₄. i, i₁ The charge density difference of nonperfect EG. Blue-green color represents charge depletion, while yellow color represents charge accumulation.

Fig. 5. Electromagnetic wave absorption properties of CuCo₂S₄@EG.

a₁–a₃ RL maps and |Z_in/Z₀| values of EG. b₁–b₃ RL maps and |Z_in/Z₀| values of CEG-2. c₁–c₃ RL maps and |Z_in/Z₀| values of CEG-4. d₁–d₃ RL maps and |Z_in/Z₀| values of CEG-6. RL maps and |Z_in/Z₀| values with different thicknesses (1.0-5.0 mm) during the frequency range of 1-18 GHz. e–h The far-field response based on the plane wave theory of PEC, CEG-2, CEG-4 and CEG-6 (1.4 mm).

Fig. 6. Heat dissipation performance and schematic of electromagnetic wave absorption of CuCo₂S₄@EG.

a Heat dissipation performance of EG, CEG-2, CEG-4 and CEG-6. b Heating and cooling curves of CEG-6 at 2.45 GHz microwave frequency. c Heating and cooling digital images of CEG-6 under the thermal infrared imager. d Schematic of electromagnetic wave absorption of CuCo₂S₄@EG.