MOF‐on‐MOF‐Derived CeO ₂ /Fe@C Composites for Tunable Low‐Frequency Electromagnetic Wave Absorption

ABSTRACT The rational design of electromagnetic wave (EMW) absorbing materials within the low‐frequency range of 2–8 GHz has significant importance. However, achieving controlled low‐frequency migration of electromagnetic materials absorption windows remains challenging. In this study, a MOF‐on‐MOF precursor (UiO‐66@MIL‐88B) is constructed via an in situ growth strategy and converted into CeO ₂ /Fe@C (CFC) composites by temperature‐programmed pyrolysis, enabling the shift of the absorption window toward lower frequencies. The optimized CFC‐2 exhibits excellent low‐frequency EMW absorption performance: the minimum reflection loss (RL _min ) is −62.20 dB at 7.84 GHz, and the effective absorption bandwidth (EAB) is 5.36 GHz at an ultrathin thickness of 1.70 mm. Notably, increasing the pyrolysis temperature enhances CeO ₂ crystallinity and shifts the optimal absorption to lower frequencies, where CFC‐3 achieves −42.54 dB at 4.00 GHz. In contrast, Fe@C and CeO ₂ @C show markedly inferior low‐frequency performance. Systematic investigation reveals that the CFC composites with abundant interfaces (Fe/CeO ₂ , CeO ₂ /C, and Fe/C), defect‐rich carbon, and oxygen vacancies. Multi‐scale interfacial polarization, coupled with magnetic loss from Fe nanoparticles, balances dielectric/magnetic losses, improves impedance matching, and enhances attenuation. This work provides a novel strategy for low‐frequency EMW absorbers by integrating MOF‐on‐MOF‐derived architectures with temperature‐programmed regulation.