Coupling radial architecture with interfacial charge redistribution in sea-urchin-like CoNi@C composites for thin and broadband microwave absorption

Co/Ni regulation tunes radial morphology and catalytic graphitization。. • Radial spines favor local-field concentration and multiple scattering. • At 1.76 mm and 15 wt%, RL = −57.86 dB with 6.39 GHz EAB, covering full Ku band. • DFT reveals composition-dependent charge redistribution at CoNi/C interfaces. • Far-field simulations predict an RCS reduction of 34.96 dB m 2 at 14.25 GHz. Reconciling low absorber loading with thin and broadband electromagnetic wave absorption remains challenging for dielectric-magnetic composites. Here, metal-organic-framework-derived sea-urchin-like CoNi@C composites were developed by coupling composition-controlled morphology evolution with in situ catalytic graphitization. Varying the Co/Ni ratio produced composition-dependent radial architectures and electromagnetic responses, with the optimized CoNi@C featuring high-aspect-ratio one-dimensional spines containing CoNi nanoparticles encapsulated by graphitic carbon. The radial spines favor geometry-induced local electric-field concentration, while the abundant CoNi/carbon interfaces promote interfacial polarization. At 15 wt% filler loading in a paraffin matrix, the optimized CoNi@C composite simultaneously achieved a reflection loss of −57.86 dB and an effective absorption bandwidth of 6.39 GHz (11.61-18.00 GHz) at a single matching thickness of 1.76 mm, covering the entire Ku band. Its strong microwave attenuation arises from the coordinated contributions of interfacial and defect polarization, charge transport, and magnetic dissipation, together with favorable impedance matching. Comparative DFT calculations further revealed composition-dependent interfacial electronic structure and charge redistribution, supporting the formation of a built-in electric field and enhanced interfacial polarization in CoNi/C. Far-field simulations demonstrated a radar cross-section reduction of 34.96 dB m 2 at 14.25 GHz. These results provide a multiscale composite-engineering strategy for low-loading, thin and broadband microwave absorbers. Download: Download high-res image (336KB) Download: Download full-size image