Abstract: The conventional selective template etching method to fabricate yolk-shell microwave absorbers is inconvenient and inefficient, so the thermally-driven contraction strategy was used to prepare asymmetric yolk-shell MnSe@C microsphere microwave absorbers via self-template directed transformation. The self-templated oriented transformation enables compositional customization and enhances the template utilization. The confinement effect of the carbon shell is crucial for realizing the thermally-driven contraction strategy and contributes to the strong conduction loss to MnSe@C. On the other hand, the enhanced polarization loss benefits from the abundant heterogeneous interfaces and defects in the asymmetric yolk-shell MnSe@C microspheres. The rich cavities in the yolk-shell structure not only facilitate optimal impedance matching, but also promote the enhancement of multiple reflection loss (RL). As a result, the asymmetric yolk-shell MnSe@C microspheres obtain excellent microwave absorption performance, the minimum RL (RL_min) and the maximum effective absorption bandwidth (EAB) reaching -54.4 dB and 5.1 GHz, respectively, at a thickness of 1.9 mm. The successful obtainment of the asymmetric yolk-shell MnSe@C microspheres paves the way for the convenient synthesis of the yolk-shell transition-metal selenides (TMSs) microwave absorbers.

Key words: Thermally-driven contraction, Yolk-shell, MnSe, Microwave absorption