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The 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.
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Functional two-dimensional high-entropy materials
Abstract Multiple principal element or high-entropy materials have recently been studied in the two-dimensional (2D) materials phase space. These promising classes of materials combine the unique behavior of solid-solution and entropy-stabilized systems with high aspect ratios and atomically thin characteristics of 2D materials. The current experimental space of these materials includes 2D transition metal oxides, carbides/carbonitrides/nitrides (MXenes), dichalcogenides, and hydrotalcites. However, high-entropy 2D materials have the potential to expand into other types, such as 2D metal-organic frameworks, 2D transition metal carbo-chalcogenides, and 2D transition metal borides (MBenes). Here, we discuss the entropy stabilization from bulk to 2D systems, the effects of disordered multi-valent elements on lattice distortion and local electronic structures and elucidate how these local changes influence the catalytic and electrochemical behavior of these 2D high-entropy materials. We also provide a perspective on 2D high-entropy materials research and its challenges and discuss the importance of this emerging field of nanomaterials in designing tunable compositions with unique electronic structures for energy, catalytic, electronic, and structural applications.
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- Award ID(s):
- 2124478
- PAR ID:
- 10436782
- Date Published:
- Journal Name:
- Communications Materials
- Volume:
- 4
- Issue:
- 1
- ISSN:
- 2662-4443
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Discovering multifunctional materials with tunable plasmonic properties, capable of surviving harsh environments is critical for advanced optical and telecommunication applications. We chose high-entropy transition-metal carbides because of their exceptional thermal, chemical stability, and mechanical properties. By integrating computational thermodynamic disorder modeling and time-dependent density functional theory characterization, we discovered a crossover energy in the infrared and visible range, corresponding to a metal-to-dielectric transition, exploitable for plasmonics. It was also found that the optical response of high-entropy carbides can be largely tuned from the near-IR to visible when changing the transition metal components and their concentration. By monitoring the electronic structures, we suggest rules for optimizing optical properties and designing tailored high-entropy ceramics. Experiments performed on the archetype carbide HfTa 4 C 5 yielded plasmonic properties from room temperature to 1500K. Here we propose plasmonic transition-metal high-entropy carbides as a class of multifunctional materials. Their combination of plasmonic activity, high-hardness, and extraordinary thermal stability will result in yet unexplored applications.more » « less
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In compositionally complex materials, there is controversy on the effect of enthalpy versus entropy on the structure and short-range ordering in so-called high-entropy materials. To help address this controversy, we synthesized and probed 40 M4AlC3 layered carbide phases containing 2 to 9 metals and found that short-range ordering from enthalpy is present until the entropy increases enough to achieve complete disordering of the transition metals in their atomic planes. We transformed all these layered carbide phases into two-dimensional (2D) sheets and showed the effects of the order vs. disorder on their surface properties and electronic behavior. This study suggests the key effect that the competition between enthalpy and entropy has on short-range order in multi-compositional materials.more » « less
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null (Ed.)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.more » « less
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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.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1038/s43246-023-00341-y
