Entropy Engineering Research Articles

In-situ reconstruction of non-noble multi-metal core-shell oxyfluorides for water oxidation

The electrochemical anodic behavior of transition metal compounds plays an undeniably non-negligible role across many electrooxidation reactions. In this work, a chronopotentiometric technique was employed to activate the multicomponent non-noble metal oxyfluorides in-situ for oxygen evolution reaction (OER). It is interesting to unravel that the increasing applied current density helps to reconstruct the catalyst into nanoporous core–shell structure and introduce metal oxyhydroxide on the surface, which guarantees more channels for efficient ion/mass transportation and thus contributes to exposing more active sites for catalytic reaction. The activated five-membered oxyfluoride shows the best catalytic activity with overpotential of 348 ± 2 mV to achieve the current density of 10 mA/cm2 and a Tafel slope of 110.3 ± 0.1 mV/dec, in contrast with the pristine one (532 ± 2 mV & 240.2 ± 0.1 mV/dec). It still maintains high stability after long time OER measurement, making it a promising succedaneum for noble metal catalysts. The high-entropy effect, amorphous state and high active sites density jointly contribute to its enhanced OER performance. This work provides new ideas for realizing the potential of inactive elements via entropy engineering and using electrochemical self-reconstruction to modify semiconductors for advanced water oxidation.

Entropy engineering promotes thermoelectric performance in p-type chalcogenides

We demonstrate that the thermoelectric properties of p-type chalcogenides can be effectively improved by band convergence and hierarchical structure based on a high-entropy-stabilized matrix. The band convergence is due to the decreased light and heavy band energy offsets by alloying Cd for an enhanced Seebeck coefficient and electric transport property. Moreover, the hierarchical structure manipulated by entropy engineering introduces all-scale scattering sources for heat-carrying phonons resulting in a very low lattice thermal conductivity. Consequently, a peak zT of 2.0 at 900 K for p-type chalcogenides and a high experimental conversion efficiency of 12% at ΔT = 506 K for the fabricated segmented modules are achieved. This work provides an entropy strategy to form all-scale hierarchical structures employing high-entropy-stabilized matrix. This work will promote real applications of low-cost thermoelectric materials.

Medium Entropy-Enabled High Performance Cubic GeTe Thermoelectrics.

The configurational entropy is an emerging descriptor in the functional materials genome. In thermoelectric materials, the configurational entropy helps tune the delicate trade‐off between carrier mobility and lattice thermal conductivity, as well as the structural phase transition, if any. Taking GeTe as an example, low‐entropy GeTe generally have high carrier mobility and distinguished zT > 2, but the rhombohedral‐cubic phase transition restricts the applications. In contrast, despite cubic structure and ultralow lattice thermal conductivity, the degraded carrier mobility leads to a low zT in high‐entropy GeTe. Herein, medium‐entropy alloying is implemented to suppress the phase transition and achieve the cubic GeTe with ultralow lattice thermal conductivity yet decent carrier mobility. In addition, co‐alloying of (Mn, Pb, Sb, Cd) facilitates multivalence bands convergence and band flattening, thereby yielding good Seebeck coefficients and compensating for decreased carrier mobility. For the first time, a state‐of‐the‐art zT of 2.1 at 873 K and average zT ave of 1.3 between 300 and 873 K are attained in cubic phased Ge0.63Mn0.15Pb0.1Sb0.06Cd0.06Te. Moreover, a record‐high Vickers hardness of 270 is attained. These results not only promote GeTe materials for practical applications, but also present a breakthrough in the burgeoning field of entropy engineering.

Ultralow thermal conductivity and improved ZT of CuInTe2 by high-entropy structure design

Entropy engineering has been widely applied to thermoelectrics as an effective strategy to reduce thermal conductivity. On the other hand，the increase of configuration entropy certainly decreases the electrical conductivity simultaneously, leading to the worsening of the thermoelectric performance. In this paper, we report a study on the high entropy structure design for chalcogenide CuInTe2. Based on the analysis of electronic band structure, we show how to optimize the constituents of high-entropy compound to relieve the influence on electrical conductivity. Compared with (CuAg)0.5(ZnGeGaIn)0.25Te2, which has the highest configuration entropy among our samples, the optimized constituents of Cu0.8Ag0.2(ZnGe)0.1(GaIn)0.4Te2 shows the one order higher carrier mobility and little bit higher thermal conductivity. Finally, the highest ZT of 1.02 at 820 K is obtained in Cu0.8Ag0.2(ZnGe)0.1(GaIn)0.4Te2, accompanying with a very low thermal conductivity of 0.5 Wm−1K−1. This work provides a successful example of the high-entropy structure design for thermoelectrics, and it indicates that to reconcile the different requirements of thermal conductivity and electrical conductivity is crucial.

Distorted thermal properties

Thermoelectrics Thermoelectric devices can convert waste heat into electricity, providing one path for improving energy efficiency. Jiang et al. leveraged entropy engineering to synthesize a single-phase high-entropy alloy with attractive thermoelectric properties. By increasing the number of elements in the alloy, the resulting disorder helps to stabilize against breakdown into multiple phases. The disordered and distorted crystal lattice suppresses thermal transport while maintaining the electrical properties, which boosts the heat-conversion efficiency of the material. Science , this issue p. [830][1] [1]: /lookup/doi/10.1126/science.abe1292

High-entropy-stabilized chalcogenides with high thermoelectric performance.

Thermoelectric technology generates electricity from waste heat, but one bottleneck for wider use is the performance of thermoelectric materials. Manipulating the configurational entropy of a material by introducing different atomic species can tune phase composition and extend the performance optimization space. We enhanced the figure of merit (zT) value to 1.8 at 900 kelvin in an n-type PbSe-based high-entropy material formed by entropy-driven structural stabilization. The largely distorted lattices in this high-entropy system caused unusual shear strains, which provided strong phonon scattering to largely lower lattice thermal conductivity. The thermoelectric conversion efficiency was 12.3% at temperature difference ΔT = 507 kelvin, for the fabricated segmented module based on this n-type high-entropy material. Our demonstration provides a paradigm to improve thermoelectric performance for high-entropy thermoelectric materials through entropy engineering.

Achieved limit thermal conductivity and enhancements of mechanical properties in fluorite RE3NbO7 via entropy engineering

Effective governance of thermal conductivity and other properties is of significant interest for science, including the fields of thermal barrier coatings, thermoelectric materials, and limit alloys. In this study, we investigated the impact of entropy engineering on properties of fluorite RE3NbO7, and limit thermal conductivity and strengthened mechanical properties are achieved. The solution strengthening mechanism leads to an 80% increase in toughness when the intrinsic stiffness and Young's modulus of the fabricated samples are identified via nanoindentation. Thermal conductivity is as low as 1.03–1.17 W m−1 K−1 at 25–900 °C, drastically reducing the gap between experimental results and theoretical limit values of fluorite RE3NbO7. The limit thermal conductivity as well as enhanced thermal expansion coefficients (11.2 × 10−6 K−1) and mechanical properties imply that the working performance of RE3NbO7 is evidently promoted by entropy engineering.

In-situ electrochemical tuning of (CoNiMnZnFe)3O3.2 high-entropy oxide for efficient oxygen evolution reactions

Abstract Nowadays, it is a challenging issue to develop efficient, stable and cost-effective electrocatalysts for oxygen evolution reaction (OER). Herein, a novel (CoNiMnZnFe)3O3.2 high-entropy oxide (M3O3.2 HEO) has been synthesized by the entropy engineering approach to exhibit a low overpotential of 336 mV at 10 mA cm−2 and a Tafel slope of 47.5 mV dec−1 in OER process. After the 20 h chronoamperometry test in 1 M KOH alkaline solution, the HEO electrode retains 86.9% of its catalytic activity. The high activity and catalytic stability in OER process can be attributed to the synergetic effect of entropy stabilization and core-shell structure, which is characterized by abundant nanosheets appear on the edge of M3O3.2 HEO core, formed with the aid of in-situ electrochemical activation.

Boosting Thermoelectric Properties of AgBi3(SeyS1-y)5 Solid Solution via Entropy Engineering.

AgBi3S5 is an environmentally friendly n-type thermoelectric material composed of earth-abundant and nontoxic elements. It has a complex monoclinic structure with distorted NaCl-type fragments, which provide its intrinsically low thermal conductivity. However, poor electrical properties limit its overall performance. Configurational entropy engineering is an effective method to enhance thermoelectric properties. With the increase of configurational entropy, phonon point defect scattering is amplified, yielding lower lattice thermal conductivity, while the structure symmetry can also be improved, which leads to the enhanced electrical transport property. In this study, we combine carrier modulation and entropy engineering, utilizing melting-annealing and spark plasma sintering, to synthesize a series of AgBi3(SeyS1-y)5.08 bulks. Se substitution effectively increases the configurational entropy and thus dramatically decreases the thermal conductivity. Moreover, anion deficiency modulation effectively optimizes the carrier concentration and the electrical transport properties. Due to a power factor of 2.7 μW/(cm·K2) and a low thermal conductivity of 0.45 W/(m·K) at 723 K, the AgBi3(Se0.9S0.1)5.08 sample possesses the highest ZT of 0.42 at 723 K, nearly double the value of AgBi3S5.08 or pristine AgBi3S5. Our work demonstrates that apart from carrier optimization, entropy engineering opens a new avenue for enhancing the thermoelectric properties of a given material.

Unveiling the Intrinsic Low Thermal Conductivity of BiAgSeS through Entropy Engineering in SHS Kinetic Process

Unveiling the Intrinsic Low Thermal Conductivity of BiAgSeS through Entropy Engineering in SHS Kinetic Process

Entropy Engineered Cubic n‐Type AgBiSe2 Alloy with High Thermoelectric Performance in Fully Extended Operating Temperature Range

AbstractDeveloping high performance n‐type thermoelectric (TE) materials is fundamentally important for developing high efficiency TE devices. AgBiSe2, which reveals superior n‐type TE performance in a cubic phase, crystallizes in a hexagonal phase at room temperature, and typically, undergoes phase transitions to a cubic phase at a temperature above 580 K. Here, for the first time, through entropy optimization with lead‐selenides (≥9.9 mol%), the high‐temperature cubic phase of AgBiSe2 is stabilized from 300 to 800 K. Furthermore, the AgBiSe2‐PbSe pseudo‐binary diagram is established. The resultant alloys with optimized entropy possess unique local distorted cubic lattices, which contribute low lattice thermal conductivity approaching 0.3 W m−1 K−1 in extended operating temperature range. Consequently, a peak figure of merit zT value of ≈0.8 at 800 K and a record‐high average zT value of 0.42 for n‐type I‐V‐VI2 compounds are attained in pure phase cubic n‐type (AgBiSe2)1−x(PbSe)x solid solutions. These results pave the way for developing new TE materials via entropy engineering.

High Entropy Engineering: New Strategy for the Critical Property Optimizations of Rare Earth Silicates

High Entropy Engineering: New Strategy for the Critical Property Optimizations of Rare Earth Silicates

Application of Entropy Engineering in Thermoelectrics

Application of Entropy Engineering in Thermoelectrics

Robust Bilayer Charge Pumping for Spin- and Density-Resolved Quantum Gas Microscopy.

Quantum gas microscopy has emerged as a powerful new way to probe quantum many-body systems at the microscopic level. However, layered or efficient spin-resolved readout methods have remained scarce as they impose strong demands on the specific atomic species and constrain the simulated lattice geometry and size. Here we present a novel high-fidelity bilayer readout, which can be used for full spin- and density-resolved quantum gas microscopy of two-dimensional systems with arbitrary geometry. Our technique makes use of an initial Stern-Gerlach splitting into adjacent layers of a highly stable vertical superlattice and subsequent charge pumping to separate the layers by 21 μm. This separation enables independent high-resolution images of each layer. We benchmark our method by spin- and density-resolving two-dimensional Fermi-Hubbard systems. Our technique furthermore enables the access to advanced entropy engineering schemes, spectroscopic methods, or the realization of tunable bilayer systems.

Stabilizing Oxygen Vacancy in Entropy-Engineered CoFe2O4-Type Catalysts for Co-prosperity of Efficiency and Stability in an Oxygen Evolution Reaction.

We used entropy engineering to design a series of CoFe2O4-type spinels. Through microstructural characterization, electrochemical measurements, and X-ray photoelectron spectroscopy, we demonstrated that the entropy-stabilized oxide (Co0.2Mn0.2Ni0.2Fe0.2Zn0.2)Fe2O4 has a single-phase spinel structure and exhibits both efficient and stable catalytic oxygen evolution. This is attributable to disordered occupation of multivalent cations, which induces severe lattice distortion and increases configurational entropy, thereby facilitating formation of structurally stable, high-density oxygen vacancies on the exposed surface of the spinel. Thus, more catalytic sites on the surface are activated and retained over the course of long-duration testing for oxygen evolution. Entropy engineering expands researchers' access to catalysts that link entropy-stabilized structures to useful properties.

High entropy phenomena induced low thermal conductivity in BiSbTe1.5Se1.5 thermoelectric alloy through mechanical alloying and spark plasma sintering

The facile synthesis approach combining the mechanical alloying (5 h) and spark plasma sintering (SPS) (11 min) of BiSbTe1.5Se1.5 high entropy alloy (HEA) is reported. High entropy engineering and nanostructuring phenomena synergistically lower the lattice thermal conductivity (<0.2 W/mK) and thermal diffusivity (<0.5 mm2/s) thus results in ultralow thermal conductivity (0.667 W/mK) at 523 K. The synthesized nanostructured HEA offers good power factor (5.51 × 10−4 W/mK2) and figure of merit (ZT) of 0.43 at 523 K.

Thermodynamic Routes to Ultralow Thermal Conductivity and High Thermoelectric Performance.

Thermoelectric (TE) research is not only a course of materials by discovery but also a seedbed of novel concepts and methodologies. Herein, the focus is on recent advances in three emerging paradigms: entropy engineering, phase-boundary mapping, and liquid-like TE materials in the context of thermodynamic routes. Specifically, entropy engineering is underpinned by the core effects of high-entropy alloys; the extended solubility limit, the tendency to form a high-symmetry crystal structure, severe lattice distortions, and sluggish diffusion processes afford large phase space for performance optimization, high electronic-band degeneracy, rich multiscale microstructures, and low lattice thermal conductivity toward higher-performance TE materials. Entropy engineering is successfully implemented in half-Huesler and IV-VI compounds. In Zintl phases and skutterudites, the efficacy of phase-boundary mapping is demonstrated through unraveling the profound relations among chemical compositions, mutual solubilities of constituent elements, phase instability, microstructures, and resulting TE properties at the operation temperatures. Attention is also given to liquid-like TE materials that exhibit lattice thermal conductivity at lower than the amorphous limit due to intensive mobile ion disorder and reduced vibrational entropy. To conclude, an outlook on the development of next-generation TE materials in line with these thermodynamic routes is given.

Multicomponent high-entropy zirconates with comprehensive properties for advanced thermal barrier coating

Thermal barrier coating materials, commonly ceramics, are deposited on superalloy surfaces to improve their service temperature. However, the intrinsic brittleness and low thermal expansion of ceramics pose a great challenge to developing new materials to replace yttria-stabilized zirconia. Herein, entropy engineering is employed to fabricate multicomponent rare earth zirconates with a large coefficient of thermal expansion, excellent mechanical properties and ultralow thermal conductivity, without sacrificing other properties. This work provides a new insight into developing novel ceramics with a combination of mechanical and thermophysical properties, which would be significant in material development for thermal barrier coatings, thermoelectric fields, etc.

Multicomponent Entropy-Stabilized Zirconates with Comprehensive Properties for Advanced Thermal Barrier Coating

Thermal barrier coating materials, commonly ceramics, are deposited on superalloy surfaces to improve their service temperature. However, the intrinsic brittleness and low thermal expansion coefficient of ceramic materials pose a great challenge to developing new materials to replace yttria-stabilized zirconia. Herein, entropy engineering is employed to fabricate multicomponent rare earth zirconates with a large thermal expansion coefficient, excellent mechanical properties and ultralow thermal conductivity, without sacrificing other properties. This work provides a new insight into developing novel ceramics with a combination of mechanical and thermophysical properties, which would be significant in material development for thermal barrier coatings, thermoelectric fields, etc.

Development of advanced materials via entropy engineering

The recent and growing interests in the metals community regarding the concept of entropy stabilization of single-phase alloys has resulted in a surge of development of other high-entropy materials via entropy engineering. This paper first briefly introduces the basic concept of entropy engineering and then summarizes its application to materials design. Moreover, perspectives regarding the entropy engineering and possible research directions are also surmised.