High‐Coordination Engineering of Asymmetrical Cerium Single‐Atoms for Advanced Electromagnetic Wave Absorption

Abstract Electromagnetic wave (EMW) absorbers are critical for addressing electromagnetic pollution and enabling stealth technologies. While metal single‐atom (M‐SA) materials have shown potential for EMW absorption, their dielectric performance is often constrained by symmetric and low‐coordination configurations. In this study, a thiourea‐mediated pyrolysis strategy is developed to construct cerium single‐atoms with asymmetric and high‐coordination environments (CeN 4 O 4 S 1.5 ). Through a combination of density functional theory calculations and experimental validation, it is found that the Ce‐SAs can induce more metal‐nonmetal dipoles and create novel nonmetal‐nonmetal dipoles compared to the low‐coordination M‐N 4 configurations, which significantly enhance their dielectric loss and EMW absorption capabilities. Additionally, the CeN 4 O 4 S 1.5 ‐based film exhibits a 6.8 GHz effective absorption bandwidth at a mere 2.3 mm thickness, alongside excellent multifunctional properties such as flexibility, thermal insulation, and flame retardancy. This work advances the understanding of the coordination environment's impact on EMW absorption and provides an efficient design strategy for next‐generation EMW absorbers.