High‐entropy alloys (HEAs) in which interesting physical, chemical, and structural properties are being continuously revealed have recently attracted extensive attention. Body‐centered cubic (bcc) ...HEAs, particularly those based on refractory elements are promising for high‐temperature application but generally fail by early cracking with limited plasticity at room temperature, which limits their malleability and widespread uses. Here, the “metastability‐engineering” strategy is exploited in brittle bcc HEAs via tailoring the stability of the constituent phases, and transformation‐induced ductility and work‐hardening capability are successfully achieved. This not only sheds new insights on the development of HEAs with excellent combination of strength and ductility, but also has great implications on overcoming the long‐standing strength–ductility tradeoff of metallic materials in general.
The “metastability‐engineering” strategy is exploited in brittle body‐centered cubic high‐entropy alloys (HEAs) via tailoring the thermal and mechanical stability of the constituent phases, and consequently, transformation‐induced ductility and work hardening capability are successfully achieved. This not only has important implications for developing high‐performance HEAs, but also sheds light on overcoming the long‐standing strength–ductility tradeoff of metallic materials in general.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Methyl formate (MF) is one of the most important chemical commodities, which has a wide range of applications. Due to environmental friendliness, mild reaction conditions, and easy operations, ...electrosynthesis of MF has garnered increasing attention in recent years. In this work, we reported an electrosynthesis route toward MF in a halide‐containing methanol solution. The thorough mechanistic investigations point out that electrosynthesis of MF is accomplished by instant reaction between aldehyde from anodic methanol oxidation, and methoxy bromide (CH3OBr) that is in‐situ generated by reaction of Br2 from anodic oxidation of Br− with methoxide (CH3O−) from cathodic reduction of methanol. This method features high atomic economy only producing valuable MF and hydrogen gas, and shows distinct advantages compared to the reported MF electrosynthesis methods. Even at 200 mA/cm2, the faradaic efficiency (FE) of MF remains consistently around 60 % at the anode while a 100 % FE hydrogen gas is produced at the cathode.
Efficient electrosynthesis of methyl formate is achieved through the facile reaction between formaldehyde produced from anodic methanol oxidation, and methoxy bromide which is in‐situ generated by reaction of Br2 from anodic oxidation of Br− and methoxide from cathodic methanol reduction. This method features high atomic economy only producing valuable methyl formate and hydrogen gas.
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Poly(lactic acid) (PLA) is regarded as one of the most promising bio-based and biodegradable polymers, due to its excellent biodegradability, biocompatibility, renewability, high strength, and easy ...processibility. However, disadvantages such as brittleness and relatively high cost have restricted its applications significantly. Polymer blending provides an economic and efficient way to modify the properties of PLA. Most shortcomings of PLA are theoretically surmountable by blending with abundant polymers with various properties. But, unfortunately, PLA is thermodynamically immiscible with most existing polymers. High-performance PLA-based blends are usually unanticipated by direct blending. In order to obtain PLA-based blends with excellent overall properties, compatibilization is required during polymer blending. Various strategies have been employed or developed to compatibilize PLA blends with different polymers, as reported in recent studies. This article aims to review the development in compatibilization strategies employed in PLA-based blends.
Recent compatibilization strategies in poly(lactic acid)-based blends have been reviewed in this paper.
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3D porous framework composed of exfoliated ultrathin nanosheets is a hot topic in the field of energy storage and conversion. A facile method to prepare 3D mesoporous C3N4 with ...few-layered nanosheets interconnected in large quantity via H2SO4 intercalation and subsequent thermal treatment was described herein. The obtained thermally-exfoliated C3N4 (TE-C3N4) was thoroughly characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), UV–Vis diffuse reflectance spectroscopy (DRS) and Brunauer–Emmett–Teller (BET) measurements. The detailed analysis indicated that TE-C3N4 possessed enlarged inter-layer space, enhanced UV-light adsorption and high specific surface area with 3D interconnected structure composed of ultrathin 2D nanosheets. Compared to bulk C3N4, TE-C3N4 showed an enhanced photocatalytic activity for photodegradation of Rhodamine B under UV-light irradiation and exhibited no significant loss of photocatalytic activity after 11 recycled runs. The pseudo-first reaction rate constant for TE-C3N4 was about four times higher than that for pure bulk-C3N4. The better photocatalytic performance could be attributed to more active catalytic sites, prolonged photo-excited carrier lifetime and shorted pathway of the carriers to the reaction sites.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Refractory high‐entropy alloys (RHEAs) show promising applications at high temperatures. However, achieving high strengths at elevated temperatures above 1173K is still challenging due to heat ...softening. Using intrinsic material characteristics as the alloy‐design principles, a single‐phase body‐centered‐cubic (BCC) CrMoNbV RHEA with high‐temperature strengths (beyond 1000 MPa at 1273 K) is designed, superior to other reported RHEAs as well as conventional superalloys. The origin of the high‐temperature strength is revealed by in situ neutron scattering, transmission‐electron microscopy, and first‐principles calculations. The CrMoNbV's elevated‐temperature strength retention up to 1273 K arises from its large atomic‐size and elastic‐modulus mismatches, the insensitive temperature dependence of elastic constants, and the dominance of non‐screw character dislocations caused by the strong solute pinning, which makes the solid‐solution strengthening pronounced. The alloy‐design principles and the insights in this study pave the way to design RHEAs with outstanding high‐temperature strength.
Structural materials with exceptional high‐temperature strengths are highly desirable for high‐temperature applications. In this work, three alloy‐design principles of the large atomic‐size and elastic‐modulus mismatches, the insensitive temperature‐dependence of elastic properties, and the dominance of non‐screw dislocations are used to design a CrMoNbV refractory high‐entropy alloy, which exhibits outperforming high‐temperature strengths.
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Oxygen, one of the most abundant elements on Earth, often forms an undesired interstitial impurity or ceramic phase (such as an oxide particle) in metallic materials. Even when it adds strength, ...oxygen doping renders metals brittle
. Here we show that oxygen can take the form of ordered oxygen complexes, a state in between oxide particles and frequently occurring random interstitials. Unlike traditional interstitial strengthening
, such ordered interstitial complexes lead to unprecedented enhancement in both strength and ductility in compositionally complex solid solutions, the so-called high-entropy alloys (HEAs)
. The tensile strength is enhanced (by 48.5 ± 1.8 per cent) and ductility is substantially improved (by 95.2 ± 8.1 per cent) when doping a model TiZrHfNb HEA with 2.0 atomic per cent oxygen, thus breaking the long-standing strength-ductility trade-off
. The oxygen complexes are ordered nanoscale regions within the HEA characterized by (O, Zr, Ti)-rich atomic complexes whose formation is promoted by the existence of chemical short-range ordering among some of the substitutional matrix elements in the HEAs. Carbon has been reported to improve strength and ductility simultaneously in face-centred cubic HEAs
, by lowering the stacking fault energy and increasing the lattice friction stress. By contrast, the ordered interstitial complexes described here change the dislocation shear mode from planar slip to wavy slip, and promote double cross-slip and thus dislocation multiplication through the formation of Frank-Read sources (a mechanism explaining the generation of multiple dislocations) during deformation. This ordered interstitial complex-mediated strain-hardening mechanism should be particularly useful in Ti-, Zr- and Hf-containing alloys, in which interstitial elements are highly undesirable owing to their embrittlement effects, and in alloys where tuning the stacking fault energy and exploiting athermal transformations
do not lead to property enhancement. These results provide insight into the role of interstitial solid solutions and associated ordering strengthening mechanisms in metallic materials.
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Lattice oxygen can play an intriguing role in electrochemical processes, not only maintaining structural stability, but also influencing electron and ion transport properties in high-capacity oxide ...cathode materials for Li-ion batteries. Here, we report the design of a gas-solid interface reaction to achieve delicate control of oxygen activity through uniformly creating oxygen vacancies without affecting structural integrity of Li-rich layered oxides. Theoretical calculations and experimental characterizations demonstrate that oxygen vacancies provide a favourable ionic diffusion environment in the bulk and significantly suppress gas release from the surface. The target material is achievable in delivering a discharge capacity as high as 301 mAh g(-1) with initial Coulombic efficiency of 93.2%. After 100 cycles, a reversible capacity of 300 mAh g(-1) still remains without any obvious decay in voltage. This study sheds light on the comprehensive design and control of oxygen activity in transition-metal-oxide systems for next-generation Li-ion batteries.
Engineering hetero-frameworks by using organic frameworks is expected to be a novel and effective strategy to facilitate the charge separation efficiency of photocatalysts. Herein, we construct a ...metal–organic framework (MOF)@covalent organic framework (COF) core–shell hetero-framework via in situ growth of a hydrazone-linked COF (TFPT–DETH) on the surface of octahedral NH 2 -UiO-66. The resultant hetero-frameworks exhibit high specific surface area with the co-existence of micropores and mesopores, extended light absorption, as well as efficient exciton dissolution and transfer. The optimal sample with an appropriate shell thickness of about 20 nm achieves an excellent hydrogen evolution rate of up to 7178 μmol g −1 h −1 , which is approximately 3 and 7 times that of pristine TFPT–DETH and its physically mixed counterpart, respectively. The concept of a hetero-framework structure may stimulate the rational design of heterostructured photocatalysts and enlarge the family of organic photocatalysts in solar energy conversion and utilization.
The oxygen redox reaction in lithium-rich layered oxide battery cathode materials generates extra capacity at high cell voltages (i.e., >4.5 V). However, the irreversible oxygen release causes ...transition metal (TM) dissolution, migration and cell voltage decay. To circumvent these issues, we introduce a strategy for tuning the Coulombic interactions in a model Li-rich positive electrode active material, i.e., Li
Mn
Ni
O
. In particular, we tune the Coulombic repulsive interactions to obtain an adaptable crystal structure that enables the reversible distortion of TMO
octahedron and mitigates TM dissolution and migration. Moreover, this strategy hinders the irreversible release of oxygen and other parasitic reactions (e.g., electrolyte decomposition) commonly occurring at high voltages. When tested in non-aqueous coin cell configuration, the modified Li-rich cathode material, combined with a Li metal anode, enables a stable cell discharge capacity of about 240 mAh g
for 120 cycles at 50 mA g
and a slower voltage decay compared to the unmodified Li
Mn
Ni
O
.
Substitution of a native ion in the crystals with a foreign ion that differs in valence (aliovalent doping) has been widely attempted to upgrade solid-state ionic conductors for various charge ...carriers including O²⁻, H⁺, Li⁺, Na⁺, etc. The doping helps promote the high-conductive framework and dredge the tunnel for fast ion transport. The garnet-type Li₇La₃Zr₂O₁₂ (LLZO) is a fast Li⁺ solid conductor, which received much attention as an electrolyte candidate for all-solid-state lithium ion batteries, showing great potential to offer high energy density and minimize battery safety concerns to meet extensive applications in large energy storage systems such as those for electric vehicles and aerospace. In the Li-stuffed garnet framework of LLZO, the 3D pathway formed by the incompletely occupied tetrahedral sites bridged by a single octahedron enables the superior Li⁺ conductivity. For optimal performance, many aliovalent-doping efforts have been made throughout metal elements (Al³⁺, Ta⁵⁺) and metalloid elements (Ga³⁺, Te⁶⁺) in the periodic table with various valences to stabilize the high-conductive phase and increase the Li vacancy concentration.
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