Developing efficient and stable earth-abundant electrocatalysts for acidic oxygen evolution reaction is the bottleneck for water splitting using proton exchange membrane electrolyzers. Here, we show that nanocrystalline CeO2 in a Co3O4/CeO2 nanocomposite can modify the redox properties of Co3O4 and enhances its intrinsic oxygen evolution reaction activity, and combine electrochemical and structural characterizations including kinetic isotope effect, pH- and temperature-dependence, in situ Raman and ex situ X-ray absorption spectroscopy analyses to understand the origin. The local bonding environment of Co3O4 can be modified after the introduction of nanocrystalline CeO2, which allows the CoIII species to be easily oxidized into catalytically active CoIV species, bypassing the potential-determining surface reconstruction process. Co3O4/CeO2 displays a comparable stability to Co3O4 thus breaks the activity/stability tradeoff. This work not only establishes an efficient earth-abundant catalysts for acidic oxygen evolution reaction, but also provides strategies for designing more active catalysts for other reactions.

Bulk polycrystalline high-entropy carbides are a newly developed group of materials that increase the limited compositional space of ultra-high temperature ceramics, which can withstand extreme environments exceeding 2000 °C in oxidizing atmospheres. Since the deformability of grains plays an important role in macromechanical performance, in this work we studied the strength and slip behaviour of grains of a spark-plasma sintered (Hf-Ta-Zr-Nb)C high-entropy carbide in a specific orientation during micropillar compression. For comparison, identical measurements were carried out on the monocarbides HfC and TaC. It was revealed that (Hf-Ta-Zr-Nb)C had a significantly enhanced yield and failure strength compared to the corresponding base monocarbides, while maintaining a similar ductility to the least brittle monocarbide (TaC) during the operation of [Formula: see text] slip systems. Additionally, it was concluded that the crystal orientation and stress conditions determine the operation of slip systems in mono- and high-entropy carbides at room temperature.

High-entropy oxides (HEOs) and medium-entropy oxides (MEOs) are new types of single-phase solid solution materials. MEOs have rarely been reported as positive electrode material for sodium-ion batteries (SIBs). In this study, we first proposed the concept of the application of MEOs in SIBs. P2-type 3-cation oxide Na2/3Ni1/3Mn1/3Fe1/3O2 (NaNMF) and 4-cation oxide Na2/3Ni1/3Mn1/3Fe1/3−xAlxO2 (NaNMFA) were prepared using the solid-state method, rather than the doping technology. In addition, the importance of the concept of entropy stabilization in material performance and battery cycling was demonstrated by testing 3-cation (NaNMF) and 4-cation (NaNMFA) oxides in the same system. Thus, NaNMFA can provide a reversible capacity of about 125.6 mAh·g−1 in the voltage range of 2–4.2 V, and has enhanced cycle stability. The capacity and decay law of the MEO batteries indicate that the configurational entropy (1.28 R (NaNMFA) > 1.10 R (NaNMF)) of the cationic system, is the main factor affecting the structural and cycle stability of the electrode material. This work emphasizes that the rational design of MEOs with novel structures and different electrochemically active elements may be the strategy for exploring high-performance SIB cathode materials in next-generation energy storage devices.

\n 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 M\n 4\n AlC\n 3\n layered carbide phases containing two to nine metals and found that short-range ordering from enthalpy was present until the entropy increased enough to achieve complete disordering of the transition metals in their atomic planes. We transformed all of these layered carbide phases into two-dimensional (2D) sheets and showed the effects of the order versus 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 multicompositional materials.\n

Achieving a synergistic improvement in the strength and ductility of metallic materials has long been a central challenge in materials science. Dislocation mobility limits both properties, making it difficult to strike a balance between them. The advent of multi-principal element alloys (also known as high-entropy alloys) offers a promising solution to this issue. Compared with conventional solid solution strengthened alloys, multi-principal element alloys exhibit greater lattice distortion. Consequently, dislocation movement must overcome higher and more frequent energy fluctuations, which consumes more energy. This increase in flow stress with increasing strain allows certain alloys to achieve enhanced work hardening capacity, leading to simultaneous improvements in both strength and ductility. However, two critical scientific questions in this area warrant further investigation: (1) Are multi-principal element alloys purely ideal random mixed structures, or is standardizing their local or multi-level microstructures necessary to achieve optimal performance? (2) How can we effectively standardize and regulate the microstructures of multi-principal element alloys? This study addresses these questions by proposing the concept of using negative mixing enthalpy (negative-enthalpy) alloying to standardize and regulate the microstructure of multi-principal element alloys. This study systematically explores how negative-enthalpy alloying can synergistically enhance strength and ductility while revealing new mechanisms of strengthening and toughening. Negative-enthalpy alloying affects the microstructure of metallic materials through three main effects: bond energy and slow diffusion, local chemical ordering, and interface and size effects. This approach provides a novel framework for designing and processing the microstructures of high-strength, high-ductility metallic materials at the atomic scale.

金属材料强度与塑性的协同提升始终是材料科学领域的核心挑战。由于材料的强度和塑性受位错可动性制约，2者通常难以协同兼顾，多主元合金(高熵合金)的出现为走出这一困境提供了新思路。相对于常规的固溶强化合金，多主元合金具有更大的晶格畸变，位错运动需要克服更高和更频繁的能量起伏，耗费更大的能量，合金流变应力随应变增加而增加，使得一些合金获得了较大加工硬化能力和强塑性协同提升。然而，该领域至少存在2个关键科学问题需要深入研究：(1) 多主元合金是完全理想的随机混合结构吗？是否需要规范其局域乃至多级微观结构来实现优异性能？(2) 如何规范和调控多主元合金微观结构？本文从规范和调控多主元合金微观结构出发，提出用负混合焓(负焓)合金化方法在原子尺度加工合金微观结构的学术思想，系统阐述利用负焓合金化方法实现合金强度与塑性协同提升，并揭示强韧化新机理。负焓合金化具有金属材料微观结构调控的3重效应：键能与慢扩散效应、局部化学有序效应、界面和尺寸效应，其为高强韧金属材料的微观结构在原子尺度设计加工提供了新维度和新范式。

Increasing the yield strength of metallic materials is observed to almost always substantially reduce their tensile ductility. Here we unravel the origin of this perplexing “strength-ductility trade-off”, and conclude that this dilemma does not necessarily preclude concurrent high strength and high ductility. We discuss several strengthening and work hardening mechanisms that regulate dislocation behavior, including traditional ones that have been pushed to their extreme in recent years, as well as new ones that take advantage of the heightened structural and chemical heterogeneities; all these mechanisms are rendered more powerful by emerging complex concentrated alloys that bring in multiple principal elements. These mechanisms, while offering elevated strength, contribute to sustainable strain hardening under high flow stresses, delaying strain localization to allow prolonged uniform elongation. The current status in the pursuit for concurrent high strength and high ductility is reviewed. The goal we set for high yield strength ~2 GPa (rivaling super steels) together with large uniform elongation ~30% (much like un-strengthened elemental metals) is projected to be soon within reach. These take-home messages shed light on some existing puzzles regarding the strength-ductility synergy, and offer new insight into the innovative design of alloys.

“Heterogeneous structures” or “heterostructures” have emerged as a cutting-edge paradigm in the field of mechanical strengthening and toughening, promising to overcome the long-standing trade-offs among strength, ductility, and toughness in metallic materials. Inspired by the multiscale design principle of natural materials, researchers have proposed a synergistic design of bioinspired “hierarchical lamellar heterostructures”, enabling exceptional and simultaneous enhancements in the strength, ductility, and toughness of metallic materials. This study reviews the theoretical foundations, design principles, and strengthening-toughening mechanisms underpinning several archetypal hierarchical lamellar heterostructures: bionic herringbone type, micro-lamellar heredity pattern, and cocoon-like dislocation network model. This review focuses on how these hierarchical lamellar heterostructures effectively overcome the strength-ductility trade-off limitations imposed by uncontrolled crack propagation, ultrafine grain structures, and high-density dislocations. It also elucidates how this heterostructure strategy and its remarkable efficacy have been successfully extended to multiple metal systems, enabling the design and fabrication of a new generation of key high-speed railway contact wires with internationally leading comprehensive performance. Finally, the review discusses the prospects for developing more advanced hierarchical lamellar heterostructured materials and explores their potential future directions.

“异质结构”或“异构”作为强韧化领域前沿构型范式，为突破金属材料的强度、塑性与韧性等难以兼顾的矛盾提供了全新的解决思路。受天然材料的跨尺度构筑启发，本研究团队提出了仿生“多级层片异构”的协同设计策略，且实现了更突出的强-塑-韧性同步提升。本文主要聚焦本研究团队多年来在多级层片异构金属材料方面的研究进展，提炼了仿生鱼骨型、微层片遗传型、蚕茧位错网型等典型多级层片异质结构的理念、设计原理和强韧化机制，重点回顾了如何有效突破不可控裂纹、超细晶组织以及高密度位错诱导的强塑性掣肘难题，并将该新型异构策略和相应的突出性能改善成功拓展至多金属体系，制备出新一代高铁关键接触线材，综合性能国际领先。最后，展望了更先进的多级层片异构材料的开发及未来潜在发展方向。

Pt-based high-entropy-alloy nanoparticles (HEA-NPs) have excellent physical and chemical properties due to the diversity of composition, complexity of surface structure, high mixing entropy, and properties of nanoscale, and they are used in a wide range of catalytic applications such as catalytic ammoxidation, the electrolysis of water to produce hydrogen, CO/CO reduction, and ethanol/methanol oxidation reaction. However, offering a facile, low-cost, and large-scale method for preparing Pt-based HEA-NPs still faces great challenges. In this study, we employed a spray drying technique combined with thermal decomposition reduction (SD-TDR) method to synthesize a single-phase solid solution from binary nanoparticles to denary Pt-based HEA-NPs containing 10 dissimilar elements loaded on carbon supports in an H atmosphere with a moderate heating rate (3 °C/min), thermal decomposition temperature (300-850 °C), duration time (30 min), and low cooling rate (5-10 °C/min). The Pt autocatalytic behavior was found and investigated, confirming that Pt element could decrease the reduction temperature of other metals via autocatalytic behavior. Therefore, using the feature of Pt autocatalytic behavior, we have achieved Pt-based HEA-NPs at a minimum temperature of 300 °C. We not only prepared a series of Pt-based HEA-NPs with targetable ingredient, size, and phase using the SD-TDR method but also proved the expandability of the SD-TDR technique by synthesizing Pt-based HEA-NPs loaded on different supports. Moreover, we investigated methanol oxidation reaction (MOR) on as-synthesized senary PtCoCuRuFeNi HEA-NPs, which presented superior electrocatalytic performance over commercial Pt/C catalyst.

Twelve different equiatomic five-metal carbides of group IVB, VB, and VIB refractory transition metals are synthesized via high-energy ball milling and spark plasma sintering. Implementation of a newly developed ab initio entropy descriptor aids in selection of candidate compositions for synthesis of high entropy and entropy stabilized carbides. Phase formation and composition uniformity are analyzed via XRD, EDS, STEM-EDS, and EXAFS. Nine of the twelve candidates form true single-phase materials with the rocksalt (B1) structure when sintered at 2473 K and can therefore be investigated as high entropy carbides (HECs). The composition (V0.2Nb0.2Ta0.2Mo0.2W0.2)C is presented as a likely candidate for further investigation as an entropy stabilized carbide. Seven of the carbides are examined for mechanical properties via nanoindentation. The HECs show significantly enhanced hardness when compared to a rule of mixtures average of the constituent binary carbides and to the highest hardness of the binary constituents. The mechanical properties are correlated to the electronic structure of the solid solutions, offering a future route to tunability of the mechanical properties of carbide ceramics via exploration of a new complex composition space. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd.

High-entropy materials have attracted considerable interest due to the combination of useful properties and promising applications. Predicting their formation remains the major hindrance to the discovery of new systems. Here we propose a descriptor-entropy forming ability-for addressing synthesizability from first principles. The formalism, based on the energy distribution spectrum of randomized calculations, captures the accessibility of equally-sampled states near the ground state and quantifies configurational disorder capable of stabilizing high-entropy homogeneous phases. The methodology is applied to disordered refractory 5-metal carbides-promising candidates for high-hardness applications. The descriptor correctly predicts the ease with which compositions can be experimentally synthesized as rock-salt high-entropy homogeneous phases, validating the ansatz, and in some cases, going beyond intuition. Several of these materials exhibit hardness up to 50% higher than rule of mixtures estimations. The entropy descriptor method has the potential to accelerate the search for high-entropy systems by rationally combining first principles with experimental synthesis and characterization.

A series of (TiZrHfVNbTa)C high-entropy ceramics with different vanadium contents have been fabricated by pressureless sintering at 2300 degrees C-2500 degrees C for 1 h, utilizing self-synthesized carbide powders obtained by carbothermal reduction. The addition of vanadium is beneficial to promote densification process and refine grain, as well as facilitate the homogeneous distribution of metal elements. The distribution of pores is also modified, almost entirely existing at grain boundary, and the integral mechanical properties achieve optimization. However, excess adding vanadium does not favor forming a single-phase (TiZrHfVNbTa)C high-entropy ceramic. The optimal (TiZrHfVNbTa)C high-entropy ceramic sintered at 2300 degrees C possesses a high relative density of 97.5 % and homogeneous microstructure with small grain size of 1.2 mu m. The flexural strength and Vickers hardness reach 473 MPa and 24.9 GPa, respectively. This work has established a cost-effective and convenient preparation of novel (TiZrHfVNbTa)C high-entropy carbide ceramics.

Owing to their unique physical and chemical properties, layered two-dimensional (2D) materials have been established as the most significant topic in materials science for the current decade. This includes layers comprising mono-element (graphene, phosphorene), di-element (metal dichalcogenides), and even multi-element. A distinctive class of 2D layered materials is the metal phosphorous trichalcogenides (MPCh, Ch=S, Se), first synthesized in the late 1800s. Having an unusual intercalation behavior, MPCh were intensively studied in the 1970s for their magnetic properties and as secondary electrodes in lithium batteries, but fell from scrutiny until very recently, being 2D nanomaterials. Based on their synthesis and most significant properties, the present surge of reports related to water-splitting catalysis and energy storage are discussed in detail. This Minireview is intended as a baseline for the anticipated new wave of researchers who aim to explore these 2D layered materials for their electrochemical energy applications.© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

High-entropy oxide (HEO) including multiple principal elements possesses great potential for various fields such as basic physics, mechanical properties, energy storage, and catalysis. However, the synthesis method of high-entropy compounds through the traditional heating approach is not conducive to the rapid properties screening, and the current elemental combinations of HEO are also highly limited. Herein, we report a rapid synthesis method for HEO through the Joule-heating of nickel foil with dozens of seconds. High-entropy rocksalt oxides (HERSO) with the new elemental combination, high-entropy spinel oxides (HESO), and high-entropy perovskite oxide (HEPO) have been synthesized through the Joule-heating. The synthesized HERSO with new elemental combinations proves to be a great promotion of OER activity due to the synergy of multiple components and the continuous electronic structure experimentally and theoretically. The demonstrated synthesis approach and the new component combination of HERSO provide a broad platform for the development of high-entropy materials and catalysts.