Computationally Guided Synthesis of MXenes by Dry Selective Extraction.

MXenes are a rapidly growing family of two-dimensional (2D) transition metal carbides and nitrides which 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 mixed surface terminations that impede MXene properties. Herein, we present a computational thermodynamic model with experimental validations 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 MXene and respective precursor compositions are systematically screened using first-principles calculations to find candidates with high phase stability and low etching energy. We further demonstrate a thermodynamic model based on the CALculation of PHAse Diagrams (CALPHAD) approach, using Ti 3 C 2 I 2 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. This article is protected by copyright. All rights reserved.