Progress in Natural Science: Materials International最新文献

Designing economical oxygen evolution reaction (OER) electrocatalysts with high activity and long-term stability is essential to promote the scale-up applications of proton exchange membrane water electrolyzer (PEMWE) for hydrogen production. Ruthenium (Ru) -based materials with high intrinsic activity are hailed as the most promising catalysts, but still infeasible for practical application considering their long unresolved poor stability (only dozens of lifespan). Thus, tremendous efforts have been devoted to uncovering the degradation mechanisms and developing stabilization strategies for the Ru-based catalysts. In this review, starting from summarizing the fundamental understanding of deactivation mechanisms, a picture of the stability issue of Ru-based catalysts is proposed, which is followed by a detailed discussion on the recently developed strategies and progress made on enhancing durability. Finally, insights on the prospects for the future development of stable and practical Ru-based OER catalysts are provided.

The primary dendrite spacing (PDS) and segregation of directionally solidified single crystal (SC) superalloy under the longitudinal magnetic field (LMF) were investigated based on the analysis of the whole cross-sectional microstructure at different solidification distances. The results show that the PDS under the LMF remains basically unchanged at different solidification distances, and it is greater than that under no LMF. With the increase of magnetic field intensity, the PDS increases and the macrosegregation decreases. The increasing PDS and reducing segregation under the LMF can be attributed to the increase of solute boundary layer, which expands the non-equilibrium freezing temperature range and brings the effective partition coefficient closer to 1. The increase of the solute enrichment layer thickness could be caused by the downward secondary circulation generated by the thermoelectric magnetic convection (TEMC) near the interface, which drives the migration of solutes towards the interdendritic region. This work not only clarifies the mechanism of LMF controlling PDS and reducing segregation by TEMC, but also provides theoretical guidance for producing high-quality SC superalloys using magnetic fields.

The standards within the global steel industry are constantly advancing, necessitating increasingly rigorous quality control protocols during the continuous casting process. Central to the challenges faced in this domain are persistent defects such as central segregation, V-shaped segregation, and center porosity, which significantly impede the production of high-caliber steel products. The discipline of electromagnetic metallurgy has emerged as a critical solution in reducing these defects, thereby enhancing the efficiency and stability of continuous casting operations. Its demonstrated effectiveness has led to its widespread implementation across global and domestic steel production industries. This paper aims to deliver a comprehensive examination of electromagnetic metallurgy's impact on the final stages of solidification in continuous casting, along with its contributions to the heating and purification processes within the tundish. Additionally, it will explore the potential advancements and applications of this technology in the evolving sphere of continuous casting.

The practical application of micro-alloying Zn–Mg alloys is limited due to their poor mechanical properties and evident strain softening behavior. Therefore, this paper proposed the utilization of ECAP plus rolling processing as an innovative approach to potentially address these limitations. Herein, effects of ECAP and rolling processing on the microstructures, mechanical properties and strain softening behavior were investigated. It was found that the grain refinement achieved through 1-pass ECAP and 8-pass ECAP processing differed significantly, and subsequent rolling processing can further regulate grain size and dislocation distribution. The 1-pass ECAP plus cold rolling (1p-CR), 1-pass ECAP plus hot-cold rolling (1p-HC), and 8-pass ECAP plus hot-cold rolling (8p-HC) processed alloys exhibited heterostructure characterized by fine grains encircling coarse grains. Additionally, regions with high density dislocations were uniformly distributed alongside regions with low density dislocations. This unique microstructure promoted the accumulation and interaction of dislocation during deformation, resulting in the inhibition of strain softening behavior while maintaining high strength and high elongation. Therefore, the 1p-CR, 1p-HC, and 8p-HC alloys demonstrated excellent formability and mechanical stability while meeting the required mechanical properties for implant materials, which highlight their significant potential for practical applications.

The welding process of aluminum (Al) alloy car body has problems such as poor weld quality, low welding coefficient, and large welding deformation. This paper mainly focuses on material accuracy design, lap structure design, simulation, and process manufacturing to break through the precision control problems caused by welding deformation of battery electric vehicle Al alloy car body. First, the 209 key functional dimensional chains of Al body-in-white are analyzed and decomposed to component and profile tolerance dimensions step by step. Moreover, the differences of vertical butt, bevel butt, and plug structures are studied and joint matching is implemented in a targeted manner. Subsequently, through welding deformation simulation analysis and welding sequence optimization, the body-in-white welding process and tooling fixtures are guided and designed to ensure that the dimensional accuracy of the Al body is controlled to ±2 ​mm in all aspects. Finally, the design of the whole vehicle arrangement of mechanical, human-machine, and major components is carried out, and an all-Al framed battery electric vehicle lightweight platform with different sizes and ranges is innovatively created. The difficulties such as the contradiction between power battery size and arrangement space, unreasonable arrangement position, and load distribution are solved.

Valley degeneracy can be broken owing to the strong spin-orbit coupling in two-dimensional transition metal dichalcogenides (2D-TMDCs). Valley-dependent interaction of carriers in TMDCs with different circular polarizations of light offers valley degree-of-freedom besides charge and spin to carry information. Thus, bandgap engineering of 2D-TMDCs plays a critical role in developing practical valleytronic devices. Hereby, we demonstrate a great enhancement in quantum yield as well as polarization of monolayer MoS₂ achieved by gradually alloying W atoms in MoS₂. By appropriately setting a time offset between the evaporation of MoO₃ and WO₃ precursors during chemical vapor deposition, a compositionally graded heterostructure of MoS₂-WS₂ monolayer can be readily grown at large scale. Raman and transmission electron microscopy measurements demonstrate that the interface possesses a steep gradient in composition, spanning from MoS₂ to WS₂ over a length ∼2 ​μm. Compared to pure monolayer MoS₂, the photoluminescence intensity at the compositionally graded interface of Mo_1-xW_xS₂ was observed to increase by a factor of 16 owing to the effective separation of photogenerated carriers by the built-in electric field. Particularly, a remarkably high polarization of 70% at 16 ​K is demonstrated for the compositionally graded interface of Mo_1-xW_xS₂, which is ∼1.4 times larger than that in MoS₂ and is attributed to the combined effect of the alloyed structure and graded bandgap. Such an engineering scheme with a graded bandgap offers new approach for the development of high-efficiency valleytronics devices.

As a promising alternative electrocatalyst to platinum for the oxygen reduction reaction (ORR), an Fe-N/C electrocatalyst with more active sites was designed by using N-doped porous crumpled graphene as carbon precursor. More defects provided by the edges and cavities of the porous crumpled graphene facilitated the anchoring and inhibited the growth of Fe clusters, and hence introduced more active sites. Furthermore, crumpled structure combined with the pores provided abundant mass transfer channels, and the fast kinetics were ensured. Consequently, the porous crumpled graphene-based catalyst showed better ORR activity and good electrochemical stability. The half-wave potential (E_1/2) of porous crumpled graphene-based catalyst was 0.69 ​V vs. RHE, and the current retention rate was above 97% after 20000s. In addition, the influence of different morphologies, degrees of defect, and compositions on the distribution of active sites and ORR performance of Fe-N/C were systematically studied, and the formation mechanism of Fe-N/C was proposed. This study provided valuable insights into designing more effective non-precious metal based electrocatalysts.

Since high-performance catalysts play a vital role in energy conversion efficiency during photocatalytic hydrogen evolution (PHE), they are indispensable for clean energy production and environmental sustainability. Though a lot of semiconductor materials have been developed as catalysts for PHE by water splitting, many of them (e.g., oxides, sulfides, and phosphides) suffer from low stability and unsuitable energy band structures. In contrast, the energy band structure of cubic silicon carbide (3C–SiC) ideally spans the water redox potential, and its suitable band gap (2.36 ​eV) can effectively utilize most of the available sunlight. Therefore, 3C–SiC exhibits unique advantages in PHE. In this review, to aid researchers in preparing an appropriate photocatalytic material for hydrogen evolution, a thorough examination of the preparation methods of 3C–SiC is offered. The modification methods of 3C–SiC and their recent advances in enhancing its efficiency of PHE are summarized. They include morphology control, heterostructure construction, doping, and loaded co-catalysts. A deep discussion of the relationship among the photocatalytic effect, its energy band structure, and modification methods of 3C–SiC is presented. Finally, the benefits and drawbacks of various modifications for PHE are emphasized, as is the outlook for future research.

With electric vehicles, energy storage systems, and portable electronic devices becoming increasingly popular, the demand for lithium-ion batteries has surged considerably. In the lithium-ion battery industry, n-methyl-2-pyrrolidone (NMP) is widely used as the solvent for cathode slurry, and polyvinylidene fluoride (PVDF) is used as the cathode binder. However, because of the harmful effect of NMP on the environment and human health, the use of NMP and PVDF for lithium-ion batteries will be highly regulated in the future. Therefore, developing eco-friendly alternatives is crucial for formulating systems using new solvents and binders. Despite numerous efforts, these alternatives have not been widely adopted across the lithium-ion battery industry. It is due to their limited ability to compete on price or performance to replace the traditional NMP/PVDF slurry formulations. This review investigates developments in the search for new solvents and binders that can be used in cathode slurry compositions. The new systems can potentially decrease energy consumption and manufacturing costs associated with NMP recovery, energy-intensive drying processes, and material expenses. We discuss key factors and technical challenges from earlier studies and compare them with the current, optimized formulations based on NMP and PVDF.

As malignant diseases are responsible for high mortality rates invariably, there is presently a pressing need to develop innovative medical diagnostic techniques due to the limitations of current approaches, including non-invasiveness, inability to monitor real-time, and the associated high cost of the equipment. Specifically, breath analysis has received a great deal of attention over the past two decades. Volatile organic compounds (VOCs) in exhaled breath could reflect the metabolic and physiological processes of the human body. Thus the electronic nose (E-nose) which comprises an array of gas sensors, signal acquisition, a pre-processing unit, and a pattern recognition algorithm that mimics the human sense of smell, can diagnose illnesses by analyzing exhaled breath fingerprints accurately, showing their irreplaceable features of non-invasive, real-time monitoring, quick diagnosis, and low cost. By combining the advantages of metal oxide semiconductor (MOS) gas sensors (fast-responding, affordable, and highly sensitive), the preponderance of MOS E-nose is further enhanced. This article focuses on metal oxide semiconductor gas sensors for detecting volatile organic compounds. The sensing principle and modification methods of binary and ternary metal oxide sensing materials are reviewed. It also encompasses a review of the metal oxide semiconductor electronic nose for detecting cancer and respiratory diseases.