Discovery of Deactivation Phenomenon in NiCo2 S4 /NiS2 Electromagnetic Wave Absorbent and Its Reactivation Mechanism.

Over the past century, extensive research has been carried out on various types of microwave absorption (MA) materials, primarily emphasizing mechanism, performance, and even toward smart device. However, the deactivation, a crucial concern for practical applications, has long been long-neglected. In this work, an in-depth exploration of the deactivation mechanism reveals a significant competition between metal and oxygen, leading to the replacement of the S-M (M = Ni and Co) bond by a new S─O bond on the surface of absorber. This substitution initiates a series of collapse effect that introduces additional defective sites and diminishes the potential for charge transport. Subsequently, passive and active anti-deactivation strategies are developed to target the deactivation. The passive strategy involved intentionally creating electron-deficient structures at the initial Ni and Co sites in the crystal through the Fe doping engineering, with the objective of preventing the generation of S─O bonds. Furthermore, the active anti-deactivation strategy allows for the precise control of absorber deactivation and reactivation by employing accelerated thermodynamic and kinetic methods, enabling a reversible transformation of S-M through competitive reactions with S─O bonds. Finally, a fast deactivation and reactivation method is first proposed promising to stimulate further innovations and breakthroughs in practical applications.