Abstract:

The growing demand for superior electromagnetic wave absorbing (EWA) materials with broad bandwidth, lightweight, as well as corrosion resistance has driven interest in molybdenum carbide-based composites. However, single-phase molybdenum carbides typically exhibit unsatisfactory impedance matching and restricted tunability of dielectric loss. Herein, we report a melamine-assisted topotactic transformation of metal-organic frameworks (MOFs) into needle-like α-MoC/β-Mo₂C composites for high-performance EWA and corrosion resistance. In this strategy, melamine serves as an additional carbon/nitrogen source and structure-directing agent. During pyrolysis, the gases released from melamine decomposition induce an in situ morphological reconstruction of the bimetallic MOF (MoZn-BIFs) precursor, significantly improving specific surface area and pore architecture, which promotes attenuation of electromagnetic waves and multiple reflections. By systematically optimizing the precursor-to-melamine mass ratio and pyrolysis temperature, we obtain the optimized α-MoC/β-Mo₂C composite (denoted MoC/Mo₂C-M₁₁T₇₀₀) at a mass ratio of 1 : 1 and a pyrolysis temperature of 700 ℃. This material exhibits a unique needle-like three-dimensional conductive network with abundant multiphase interfaces, effectively promoting interfacial polarization and dielectric loss. Remarkably, at a filler loading of only 30 wt% and a matching thickness of 2.025 mm, the MoC/Mo₂C-M₁₁T₇₀₀ achieves a minimum reflection loss (RL_min) of -63.61 dB. Its total effective absorption bandwidth over the thickness range of 1– 4 mm (EAB_total) is 12.61 GHz (covering 5.39–18 GHz), demonstrating excellent broadband EWA performance. Furthermore, the material shows good corrosion resistance. This work clarifies the mechanism behind the formation of the dual-phase heterostructure and its influence on electromagnetic parameters, providing a facile and controllable route for developing high-performance, multifunctional molybdenum carbide-based absorbers.

Key words: α-MoC/β-Mo₂C, Topotactic transformation, Electromagnetic wave absorption, Corrosion resistance