Temperature-Tailored Synthesis of Ultrasmall Mo ₂ C/N-Doped Carbon Composites: Architecting Heterointerfaces for Enhanced Microwave Absorption

Integrating secondary carbides into a carbon matrix is recognized as an effective approach for developing high-performance electromagnetic wave absorption materials. However, the synthesis of carbides with ultrasmall sizes and their homogeneous dispersion within the matrix have long been significant challenges. In this study, a novel Mo₂C/C composite, where ultrasmall Mo₂C particles (less than 3.0 nm) are decorated on N-doped carbon, is successfully fabricated. Cheap tartaric acid and ammonium molybdate are employed as precursors and then subjected to a pyrolysis process. The pyrolysis temperature, ranging from 600 to 800 °C, is precisely controlled to regulate the reaction between molybdenum and the carbon substrate, thereby controlling the particle size and content of molybdenum carbide and their surface chemical states. This temperature-dependent modulation is crucial because it allows for optimization of the dielectric parameters of the Mo₂C/C composite, thereby enhancing its microwave absorption capability. The resulting Mo₂C/C composite demonstrates outstanding performance, with an optimized effective absorption band (EAB) of 4.15 GHz at a thickness of 2.3 mm and a cumulative bandwidth of 12.80 GHz within the thickness range 1.0-5.0 mm. Mechanistic investigations reveal that the impressive microwave absorption is attributed to multiple loss mechanisms, including interface polarization, dipole polarization, and conduction loss, which are facilitated by numerous heterointerfaces created by ultrasmall Mo₂C particles, the carbon matrix, and N doping. Finite-element simulation further validates its promising prospects for practical applications, paving a new way for constructing excellent Mo₂C/C composites with ultrasmall particle sizes as microwave absorption materials.