Quasi‐Binary Transition Metal Dichalcogenide Alloys: Thermodynamic Stability Prediction, Scalable Synthesis, and Application

Abstract

Transition metal dichalcogenide (TMDCs) alloys could provide a wide range of physical and chemical properties, ranging from charge density waves to superconductivity and electrochemical activities. While many exciting behaviors of unary TMDCs have been predicted, the vast compositional space of TMDC alloys has remained largely unexplored due to our lack in understanding of their stability when accommodating different cations or chalcogens in a single-phase. Here, we report a theory-guided synthesis approach to achieve unexplored quasi-binary TMDC alloys through computationally predicted stability maps. We have generated equilibrium temperature-composition phase diagrams using first-principles calculations to identify the stability for 25 quasi-binary TMDC alloys, including those involving non-isovalent cations and verify them experimentally by synthesizing a subset of 12 predicted alloys using a scalable chemical vapor transport method. We demonstrate that the synthesized alloys can be exfoliated into 2D structures, and some of them exhibit: (i) outstanding thermal stability tested up to 1230 K, (ii) exceptionally high electrochemical activity for CO 2 reduction reaction in a kinetically limited regime with near zero overpotential for CO formation, (iii) excellent energy efficiency in a high rate Li-air battery, and (iv) high break-down current density for interconnect applications. This framework can be extended to accelerate the discovery of other TMDC alloys for various applications.As a class of 2D materials, transition metal dichalcogenides (TMDCs) display diverse physical properties, including topological insulator properties, [1,2] superconductivity, [3][4][5][6] valley polarization, [7][8][9][10] and enhanced electrocatalytic activity for various chemical reactions. [11][12][13][14][15][16][17][18] This diversity arises due to the ability of TMDCs to accommodate different transition-metal elements, such as Mo, W, V, Nb, Ta, Re and others, with the three chalcogens (S, Se, and Te) in stable layered structures -that can be exfoliated to a desired number of 2D layers to control quantum confinement. Their properties can be further tuned

2D High‐Entropy Transition Metal Dichalcogenides for Carbon Dioxide Electrocatalysis

“…We refer to the minimum growth temperature above which the alloy is miscible as its miscibility temperature T misc , which can be calculated using first-principles methods, as has been shown for binary alloys in a recent work. [8] HEAs take advantage of the increase in configurational entropy due to the large number of components to stabilize a single-phase solid solution, even though pairwise alloys of the components might be immiscible. But because the number of required calculations to determine T misc scales exponentially with the number of alloy components, this method is intractable for HEAs.…”

“…Unary free energies are also shown for MoS 2 , VS 2 , and Ag. miscibility gaps; [8] thus, the increase in configurational entropy upon including many principal components is important for stabilizing a TMDC alloy with V and group VI transition metals.…”

Phase‐Dependent Band Gap Engineering in Alloys of Metal‐Semiconductor Transition Metal Dichalcogenides

“…The phase diagram is generated by looping over a grid of temperature values and determining the binodal and spinodal boundaries with the common tangent construction and curvature of the free energy, respectively (Section S1, Supporting Information). [14] Figure 1a shows the enthalpy and the free energy at the synthesis temperature (1350 K) of the 1T and 2H phases of Mo 1-x Nb x Se 2 . The 2H phase is predicted to be more stable at every molar concentration over the 1T phase, but it is immiscible at T = 0 K due to a positive mixing enthalpy.…”

2D Layered Material Alloys: Synthesis and Application in Electronic and Optoelectronic Devices

“…For example, recently, Hemmat et al have excavated 25 kinds of 2DLM alloys through the equilibrium temperature-composition phase diagrams acquired by first-principles calculations, and they have synthesized 12 of them by employing a single CVT approach. [306]…”