Computationally Guided Synthesis of MXenes by Dry Selective Extraction

• Published in: Advanced materials (Weinheim) Vol. 35; no. 45; pp. e2305200 - n/a
• Main Authors: Rems, Ervin, Anayee, Mark, Fajardo, Eiara, Lord, Robert L., Bugallo, David, Gogotsi, Yury, Hu, Yong‐Jie
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.11.2023
• Subjects: CALPHAD; Chemical etching; Composition; dry selective extraction; Energy storage; Etchants; First principles; first‐principles calculations; Fluorine; Gibbs free energy; halogen etching; Iodine; Materials science; Metal carbides; MXenes; Phase diagrams; Phase stability; Precursors; Synthesis; Thermodynamic models; Thermodynamics; Transition metals; Vapor pressure
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202305200

MXenes are a rapidly growing family of 2D transition metal carbides and nitrides that are promising for various applications, including energy storage and conversion, electronics, and healthcare. Hydrofluoric‐acid‐based etchants are typically used for large‐scale and high‐throughput synthesis of MXenes, which also leads to a mixture of surface terminations that impede MXene properties. Herein, a computational thermodynamic model with experimental validation is presented to explore the feasibility of fluorine‐free synthesis of MXenes with uniform surface terminations by dry selective extraction (DSE) from precursor MAX phases using iodine vapors. A range of MXenes and respective precursor compositions are systematically screened using first‐principles calculations to find candidates with high phase stability and low etching energy. A thermodynamic model based on the “CALculation of PHAse Diagrams” (CALPHAD) approach is further demonstrated, using Ti3C2I2 as an example, to assess the Gibbs free energy of the DSE reaction and the state of the byproducts as a function of temperature and pressure. Based on the assessment, the optimal synthesis temperature and vapor pressure are predicted and further verified by experiments. This work opens an avenue for scalable, fluorine‐free dry synthesis of MXenes with compositions and surface chemistries that are not accessible using wet chemical etching. The feasibility of a dry, fluorine‐free MXene synthesis route is investigated through quantum mechanics calculations and thermodynamic modeling. Computational insights are experimentally validated to demonstrate synthesis of MXenes through dry selective extraction (DSE) of MAX phase precursors using iodine vapor under suitable temperatures and pressures. The DSE approach opens avenues for the sustainable and scalable synthesis of new MXenes.