Enhancing the Low/Middle-Frequency Electromagnetic Wave Absorption of Metal Sulfides through F⁻ Regulation Engineering

Fluorine ion (F⁻) regulation engineering rarely has been presented as a promising strategy for obtaining high-performance electromagnetic wave (EMW) absorbing materials, and the related EMW attenuation mechanism has never been elucidated. Herein, a new F⁻ regulation strategy is demonstrated for the first time, giving rise to broad low-/middle-frequency EMW attenuation by synergistically manipulating multiple factors, such as the morphology, composition, interface, defects, and conductivity. It is found that both the F⁻ concentration and its introduction method (i.e., in situ or post-treatment) are significant. Because of the in situ introduced heterointerfaces, the enriched defects, appropriate composition, and electronic conductivity, improvements in impedance matching and F⁻-regulated dielectric loss are simultaneously achieved. Accordingly, the optimized NiCo₂S₄/Co_1−xS/Co(OH)F composite delivered an effective absorption band of 6.03 GHz (4.57–10.60 GHz), which is five times higher than the pure counterpart, making it the only sulfide-based absorber with a broad absorption feature toward the low frequency (from 4 GHz) with a small thickness (<3 mm) to date. In short, this work not only expounds on the unique roles of F⁻ in chemical synthesis, microstructure design, and EMW absorption but also offers a viable strategy for solving the low-/middle-frequency EM interference issues through F⁻ regulation engineering.