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

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_xT_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 Ni²⁺ and Fe³⁺ on zeolitic imidazolate framework-67, leading to a tunable magnetic response. The hollow FeCoNi@NCMs-C_xT_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_xT_y in marine environments, FeCoNi@NCMs-C_xT_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.