Seed‐Assisted In Situ Growth Coupled With Rapid Joule Heating for Defect Engineering of ZIF‐67‐Derived Carbon Nanofibers Toward Broadband Microwave Absorption

Addressing electromagnetic wave pollution requires lightweight absorbers with strong absorption, broad bandwidth, and small thickness. This work introduces a structural regulation strategy combining seed‐assisted in situ growth with rapid Joule heating (RJH) to fabricate C/Co composite nanofibers from ZIF‐67. The “cobalt seeds” enable high‐density, uniform ZIF‐67 loading, preventing nanoparticle agglomeration; the 5 s RJH process induces nonequilibrium carbonization, preserving abundant carbon defects and inhibiting cobalt particle coarsening. The optimized Co‐CNF‐2 exhibits high specific surface area, high defect density, and numerous C/Co heterointerfaces, leading to enhanced interface polarization, dipole polarization, and magnetic loss while maintaining moderate conduction loss. Remarkably, Co‐CNF‐2 achieves a minimum reflection loss of –60.11 dB at 2.47 mm and a maximum effective absorption bandwidth of 6.80 GHz at 2.46 mm, covering the entire Ku band. Mechanistic studies reveal that metallic Co is the primary contributor to magnetic loss, whereas surface‐trace CoO and carbon defects facilitate polarization relaxation and optimize impedance matching. This work provides new insights for the rapid construction of multi‐mechanism metal–organic frameworks (MOFs) derived one‐dimensional absorbers.