Confined Diffusion Engineering of FeCoNi‐Embedded Hollow Carbon Microcage toward Controllable Electromagnetic Wave Absorption and Anticorrosive Polyvinylidene Fluoride Composite in Marine Environment

Abstract Rational regulation of hollow magnetic‐dielectric composites is becoming a leading strategy for achieving superior electromagnetic (EM) wave absorption. However, the simple fabrication of such composites remains a challenge. Herein, a confined diffusion engineering strategy is exploited to prepare hollow magnetic‐dielectric microcages, specifically FeCoNi@NCMs‐C x T y . Driven by Kirkendall effect, the alloying and migration of magnetic nanoparticles result in the formation of core–shell magnetic nanoparticle@graphitic carbon heterojunctions and graphitic carbon domains. Moreover, the metal content can be controlled by adjusting the etching of Ni 2+ and Fe 3+ on zeolitic imidazolate framework‐67, leading to a tunable magnetic response. The hollow FeCoNi@NCMs‐C x T y exhibits controllable EM wave absorption performance in the C∼Ku band, with the minimum reflection loss (RL min ) decreasing from ‐46.2 dB to ‐46.6 dB and ‐52.8 dB. Accordingly, the effective absorption bandwidth (EAB) expands from 1.63 GHz in the C band to 3.48 GHz in the C ∼ X band and 4.88 GHz in the X ∼ Ku band. To expand the application of FeCoNi@NCMs‐C x T y in marine environments, FeCoNi@NCMs‐C x T y /polyvinylidene fluoride composite is fabricated using a monolayer membrane‐mediated microscale processing method, showing anti‐corrosive properties. This study presents a novel strategy for fabricating high‐performance EM wave absorption composite that hold great potential in C∼Ku bands and for use in marine environments.