High-Entropy 2D Carbide MXenes—TiVNbMoC₃ and TiVCrMoC₃

In the first decade of research detailing 2D MXenes, methods to produce MXenes with one or two transition metals (M) were reported. Inspired by the two fast-growing fields of high-entropy compounds and 2D MXenes, We recently synthesized two multi-principal-element high-entropy M₄C₃T<i>_x</i> MXenes, TiVNbMoC₃T<i>_x</i> and TiVCrMoC<i>₃</i>T<i>_x</i> as well as their precursor TiVNbMoAlC₃ and TiVCrMoAlC₃ high-entropy MAX phases. We used X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDS) to study the phase composition and establish equimolar stoichiometry 1:1:1:1 for the four principal transition metal elements Ti:V:Nb:Mo and Ti:V:Cr:Mo in these MXenes. Scanning transmission electron microscopy (STEM) studies were used to determine structure and the distribution of the M elements in these M₄C₃T<i>_x</i> MXenes. First-principles calculations were used to compute the formation energies and to further explore synthesizability of these high-entropy phases. To further evaluate the effect of entropic stabilization in these systems, we evaluated the phase formation of the high-entropy MAX phases using non-equimolar transition metals, such as Ti:V:Nb:Mo 1.3:1.3:1.3:0.1. In this talk we describe the formation of high-entropy MXenes and their precursors and our recent understanding of these phases. The synthesis of high-entropy MXenes significantly expands the compositional variety of the MXene family to further tune their properties, including electronic, magnetic, electrochemical, catalytic, high temperature stability, and mechanical behavior.