Ultrasmall Mo₂C Nanoparticle-Decorated Carbon Polyhedrons for Enhanced Microwave Absorption

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.