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.