Cross-scale structural engineering of MOF-derived Co_xNi_y@C nanorods with controllable electromagnetic response behavior for broadband electromagnetic wave absorption

Metal‒organic framework (MOF) derivatives employed as electromagnetic wave (EMW) absorption materials have gained considerable attention because of their plentiful coordination components and diverse nanomicrostructures. However, achieving broadband EMW absorption solely through nanoscale structural design remains challenging. Herein, a cross-scale structural engineering strategy is proposed to address this limitation. At the nanomicroscale, MOF-derived Co_xNi_y@C nanorods were fabricated via a solvothermal and pyrolysis process. Systematic manipulation of the built-in electric field (BIEF) heterointerface achieved through adjusting the Co/Ni atomic ratio significantly promotes electron-directed migration, alters the spatial charge distribution, and ultimately enhances the polarization relaxation and magnetic resonance effects, resulting in superior EMW absorption performance (the effective absorption bandwidth of Co₂Ni@C is 4.9 GHz at 1.75 mm). The geometric configuration of the electromagnetic metastructures was subsequently optimized via CST software. Through cross-scale structural design, the simulated gradient honeycomb structure metamaterial composed of Co₂Ni@C achieves multiband compatibility, and the EAB reaches 38 GHz (covering 2–40 GHz) with a total thickness of 15 mm. This research elucidates the BIEF loss mechanism of MOF-derived Co_xNi_y@C composites by rationally controlling the Co/Ni atomic ratio and provides novel insights into the structural design of electromagnetic nanomaterials.