Abstract: To address long-standing challenges associated with MXene-based materials, such as impedance mismatch and limited loss mechanisms, in multi-frequency electromagnetic wave (EMW) absorption applications, this work proposes a hybrid strategy integrating Lewis molten salt-assisted etching with gradient oxidation kinetics. This strategy enables the precise in situ oxidation of MXene surfaces, yielding MXene/TiO₂ heterostructures characterized by abundant heterogeneous interfaces and tunable dielectric response properties. Notably, the MXene/TiO₂-200 heterostructures obtained through oxidation at a low temperature of 200 °C demonstrate exceptional multi-frequency EMW absorption performance, achieving a reflection loss (R_L) of up to -52.2 dB at a frequency of 8.0 GHz with a thickness of only 2.0 mm. Meanwhile, an effective absorption bandwidth (EAB) of 2.6 GHz is achieved at a matching thickness of 1.7 mm. In-depth analysis of electromagnetic parameters, combined with electromagnetic simulation calculations, reveals that the heterogeneous structure exhibits significant interface polarization and conduction loss characteristics, thereby substantially enhancing the dielectric loss capability. Radar cross section (RCS) simulation results further validate the material's immense potential for radar stealth applications, demonstrating a RCS reduction of 11.8 dB m². This work establishes a straightforward design paradigm for the development of high-performance MXene-based materials for EMW absorption.

Key words: Lewis molten salt, Gradient oxidation, Multi-frequency, Heterostructures, Electromagnetic wave absorption