No abstract

High‐entropy alloys combine multiple principal elements at a near equal fraction to form vast compositional spaces to achieve outstanding functionalities that are absent in alloys with one or two principal elements. Here, the prediction, synthesis, and multiscale characterization of 2D high‐entropy transition metal dichalcogenide (TMDC) alloys with four/five transition metals is reported. Of these, the electrochemical performance of a five‐component alloy with the highest configurational entropy, (MoWVNbTa)S2, is investigated for CO2 conversion to CO, revealing an excellent current density of 0.51 A cm−2 and a turnover frequency of 58.3 s−1 at ≈ −0.8 V versus reversible hydrogen electrode. First‐principles calculations show that the superior CO2 electroreduction is due to a multi‐site catalysis wherein the atomic‐scale disorder optimizes the rate‐limiting step of CO desorption by facilitating isolated transition metal edge sites with weak CO binding. 2D high‐entropy TMDC alloys provide a materials platform to design superior catalysts for many electrochemical systems.

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

electrochemical reactions. [1][2][3][4][5][6][7][8][9][10][11] In particular, molybdenum disulfide (MoS 2 ) and a few members of transition metal dichalcogenides (TMDCs) in contact with ionic-liquid (IL) electrolyte have recently shown a great promise to overcome fundamental electronic and thermokinetic limitations for CO 2 reduction reaction, as well as the oxygen reduction and evolution reactions (ORR/OER). [7][8][9][10] These studies have been conducted on a limited number of TMDCs, and the majority of other TMDCs with a wide range of electronic and potentially catalytic properties have not been investigated. In this study, we report synthesis and characterization of a wide range of TMDCs including sulfides, selenides, and tellurides of group V and VI transition metals and study their electrochemical performance in aprotic medium with Li salts. We employ a wide suite of characterization techniques, such as scanning transmission electron microscopy (STEM), energy dispersive spectroscopy (EDS), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), dynamic light scattering (DLS), and atomic forceThe optimization of traditional electrocatalysts has reached a point where progress is impeded by fundamental physical factors including inherent scaling relations among thermokinetic characteristics of different elementary reaction steps, non-Nernstian behavior, and electronic structure of the catalyst. This indicates that the currently utilized classes of electrocatalysts may not be adequate for future needs. This study reports on synthesis and characterization of a new class of materials based on 2D transition metal dichalcogenides including sulfides, selenides, and tellurides of group V and VI transition metals that exhibit excellent catalytic performance for both oxygen reduction and evolution reactions in an aprotic medium with Li salts. The reaction rates are much higher for these materials than previously reported catalysts for these reactions. The reasons for the high activity are found to be the metal edges with adiabatic electron transfer capability and a cocatalyst effect involving an ionic-liquid electrolyte. These new materials are expected to have high activity for other core electrocatalytic reactions and open the way for advances in energy storage and catalysis. ElectrocatalystsThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

Single-nanocrystal fluorescence microscopy reveals that the immiscibility between PbBr2 and CH3NH3PbBr3 crystals imposes the limiting energetic barrier for nanocrystal conversion.