Cross-scale structural engineering of MOF-derived Co _<i>x</i> Ni _<i>y</i> @C nanorods with controllable electromagnetic response behavior for broadband electromagnetic wave absorption

Metal-organic frameworks (MOF) derivatives employed as electromagnetic wave (EMW) absorption materials have gained considerable attention because of their plentiful coordination components and diverse nano-micro structures. However, achieving broadband EMW absorption solely through nano‑microscale structural design remains challenging. Herein, a cross-scale structural engineering strategy is proposed to address this limitation. At the nano-microscale, MOF-derived Co_xNi_y@C nanorods were fabricated via a solvothermal and pyrolysis process. Systematic manipulation of the built-in electric field (BIEF) heterointerfaces achieved through adjusting the Co/Ni atomic ratio significantly promotes electron-directed migration, alters spatial charge distribution, and ultimately enhances the polarization relaxation and magnetic resonance effects, resulting in the superior EMW absorption performance (the effective absorption bandwidth of Co₂Ni@C is 4.9 GHz at 1.75 mm). Then, the geometric configuration of the electromagnetic metastructures was optimized using CST software. Through cross-scale structural design, the simulated gradient honeycomb structure metamaterial composed of Co₂Ni@C achieves multi-band compatibility, the EAB reaching 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.