Cavity Structure Evolution Based on Asymmetric Diffusion for Efficient Electromagnetic Wave Absorption

Abstract Ion exchange engineering offers dual advantages in designing electromagnetic wave absorbing (EWA) materials: atomic component reconstruction drives mesoscopic structural evolution, synergistically surpassing traditional material properties. However, quantifiable prediction of diffusion barriers, ion migration pathways across interfaces, and multiscale modulation mechanisms remains unclear. Herein, diffusion kinetic differences are leveraged to construct a multigradient platform based on the nano‐Kirkendall effect, enabling directed exchange of Fe 3 ⁺ with Ni 2 ⁺ in Ni‐MOF. Thanks to the electron transfer polarization of the multi‐component heterointerface and the unique dielectric sensitivity of the cavity structure, the composite material exhibits excellent electromagnetic wave absorption performance, achieving an ultra‐wide effective bandwidth of 7.21 GHz at a thickness of 1.83 mm, with a minimum reflection loss of −50.14 dB. Furthermore, simulation calculations are utilized to reveal the mechanism by which the shell thickness of the cavity structure regulates the electromagnetic response of the material, as well as the mechanism of electron transfer polarization at the heterointerface. This study elucidates the intrinsic mechanism of ion exchange engineering in regulating the electromagnetic response of materials, and also provides new insights for the structural design of high‐performance EWA materials.