Ultrasmall Mo₂C Nanoparticle-Decorated Carbon Polyhedrons for Enhanced Microwave Absorption

Abstract

Carbides/carbon composites are becoming a new kind of microwave absorption (MA) materials with great potential in chemical stability and light weight, as well as enhanced performance. Herein, we design a series of Mo2C/C composites through a simple pyrolysis of Mo-substituted ZIF-8 (Mo/ZIF-8). It is found that the transformation of zeolitic imidazolate frameworks into carbon polyhedrons is accompanied by the in situ formation of ultrasmall Mo2C nanoparticles (Mo2C NPs) less than 5.0 nm. The molar ratio of 2-methylimidazole to molybdic acid (MIM/Mo) presents a significant effect on the relative content of Mo2C NPs but not on their average size. The uniform distribution of Mo2C NPs in carbon polyhedrons overcomes the poor chemical homogeneity in conventional carbides/carbon composites. More importantly, Mo2C NPs modulate the dielectric loss of these composites effectively. On one hand, they moderately weaken the contribution from conductivity loss and dipole orientation polarization; on the other hand, they create considerable interfacial polarization. As a result, these Mo2C/C composites display much better impedance matching than individual carbon polyhedrons. When the MIM/Mo ratio reaches 6.0, the optimized composite, S-Mo2C/C-6.0, displays good MA performance in the frequency range of 2.0–18.0 GHz, including powerful reflection loss and broad qualified bandwidth. Its performance is actually superior to those conventional carbides/carbon composites in previous studies, demonstrating that Mo2C/C composite from this novel strategy may be a promising candidate for high-performance MA materials in the future.