Degradation Chemistry and Kinetic Stabilization of Magnetic CrI₃

The discovery of the intrinsic magnetic order in single-layer chromium trihalides (CrX₃, X = I, Br, and Cl) has drawn intensive interest due to their potential application in spintronic devices. However, the notorious environmental instability of this class of materials under ambient conditions renders their device fabrication and practical application extremely challenging. Here, we performed a systematic investigation of the degradation chemistry of chromium iodide (CrI₃), the most studied among CrX₃families, via a joint spectroscopic and microscopic analysis of the structural and composition evolution of bulk and exfoliated nanoflakes in different environments. Unlike other air-sensitive 2D materials, CrI₃undergoes a pseudo-first-order hydrolysis in the presence of pure water toward the formation of amorphous Cr(OH)₃and hydrogen iodide (HI) with a rate constant of k_I= 0.63 day^-1without light. In contrast, a faster pseudo-first-order surface oxidation of CrI₃occurs in a pure O₂environment, generating CrO₃and I₂with a large rate constant of k_Cr= 4.2 day^-1. Both hydrolysis and surface oxidation of CrI₃can be accelerated via light irradiation, resulting in its ultrafast degradation in air. The new chemical insights obtained allow for the design of an effective stabilization strategy for CrI₃with preserved optical and magnetic properties. The use of organic acid solvents (e.g.,