Graded Spherical CoFe/C Composites Derived from Bimetallic Metal-Organic Frameworks Enable Ultra-Broadband High-Efficiency Electromagnetic Wave Absorption

Carbon-based magnetic composites derived from metal-organic frameworks (MOFs) have emerged as promising candidates for electromagnetic wave absorption. In this study, graded structured spherical cobalt-iron/carbon (CoFe/C) composites were fabricated via a stepwise in-situ pyrolysis strategy using bimetallic CoFe-MOF precursors. The composite pyrolyzed at 700 ℃ exhibits exceptional microwave absorption properties: it achieves a minimum reflection loss (RL) of −80.3   dB at 9.68   GHz with a 3.00   mm thickness, along with an effective absorption bandwidth (EAB, RL < −10   dB) of 4.8   GHz (7.9–12.7   GHz), fully covering the entire X-band. Notably, when the thickness decreases to 2.20   mm, the EAB expands to 6.7   GHz (11.3–18.0   GHz), spanning the complete Ku-band. Mechanistic analysis reveals that the superior performance arises from two critical factors: optimized impedance matching enabled by synergistic dielectric and magnetic loss mechanisms, and intensified electromagnetic wave scattering through the graded spherical architecture. This work provides a scalable synthesis protocol for bimetallic composites while demonstrating a rational design strategy for high-performance broadband microwave absorbers.