Ultrathin Conductive Interlayer with High-Density Antisite Defects for Advanced Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries are promising next-generation rechargeable batteries due to thier high energy density, low cost, and environmental friendliness. However, the extremely low electrical conductivity of sulfur and the dissolution of polysulfides limit their actual electrochemical performances, especially in the case of high sulfur mass loading. Here, a new strategy based on intrinsic point defects of materials is proposed to simultaneously enhance the electrical conductivity of active material and regulate the migration of polysulfides. Taking advantage of ultrathin and lightweight Bi₂Te_2.7Se_0.3 (BTS) interlayers with high-density antisite defects on the separator surface, the Li–S battery with BTS interlayer shows a capacity of 756 mAh g⁻¹ at 2C and a low capacity decay rate of 0.1% over 300 cycles. The BTS interlayer can not only enhance the active material utilization but also improve capacity retention. The defect engineering strategy accompanied with facile method is promising for the development of advanced Li–S batteries for practical application.     

High-Density Frenkel Defects as Origin of N-Type Thermoelectric Performance and Low Thermal Conductivity in Mg3Sb2-Based Materials

Mg₃Sb₂-based intermetallic compounds with exceptionally high thermoelectric performance exhibit unconventional n-type dopability and anomalously low thermal conductivity, attracting much attention to the underlying mechanisms. To date, investigations have been limited to first-principle calculations and thermodynamic analysis of defect formation, and detailed experimental analysis on crystal structure and phonon modes has not been achieved. Here, a synchrotron X-ray diffraction study clarifies that, against a previous view of a simple crystal structure with a small unit cell, Mg₃Sb₂ is inherently a heavily disordered material with Frenkel defects, charge-neutral defect complexes of cation vacancies and interstitials. Ionic charge neutrality preserved in Mg₃Sb₂ is responsible for exotic n-type dopability, which is unachievable for other Zintl phase materials. The thermal conductivity of Mg₃Sb₂ exhibits deviation from the standard T⁻¹ temperature dependency with strongly limited phonon transport due to a strain field. Inelastic X-ray scattering measurement reveals enhanced phonon scattering induced by disorder. The results will draw renewed attention to crystal defects and disorder as means to explore new high-performance thermoelectric materials.     

Robust and High Photoluminescence in WS2 Monolayer through In Situ Defect Engineering

The photoluminescence quantum yield (PLQY) of the chemical vapor deposition (CVD) grown transition-metal dichalcogenides (TMDs) films is often much lower than their mechanically exfoliated counterparts, making the coexistence of large-area and high PLQY in TMDs monolayer a huge challenge. Here, an in situ defect engineering strategy is reported to fundamentally dilutes the impact of intrinsic sulfur vacancy on tungsten disulfide (WS₂) monolayer. By ingeniously incorporating oxygen atoms in the sulfur vacancy sites of WS₂ lattice via the CVD method, oxygen doped WS₂ monolayer exhibits remarkably improved optical properties. The PLQY is uniformly enhanced by nearly two orders and can reach up to 9.3%, which is even higher than mechanically exfoliated counterparts. Besides, strong W-O bonds endow materials with superior environment stability, and the high PLQY could persist with an endurance of up to 3 months under ambient conditions without any protection. More in-depth insights from the first-principle calculations illustrate that the enhancement mechanism is the synthetic action of the suppression of nonradiative recombination and conversion from trion to neutral, and the excellent stability arises from repaired saturated coordination bonds at sulfur vacancy sites. This method opens up more possibilities for both fundamental exciton physics and optoelectronics applications.     

Simultaneously Tuning Band Structure and Oxygen Reduction Pathway toward High-Efficient Photocatalytic Hydrogen Peroxide Production Using Cyano-Rich Graphitic Carbon Nitride

The demands for green production of hydrogen peroxide have triggered extensive studies in the photocatalytic synthesis, but most photocatalysts suffer from rapid charge recombination and poor 2e⁻ oxygen reduction reaction (ORR) selectivity. Here, a novel composite photocatalyst of cyano-rich graphitic carbon nitride g-C₃N₄ is fabricated in a facile manner by sodium chloride-assisted calcination on dicyandiamide. The obtained photocatalysts exhibit superior activity (7.01 mm  h⁻¹ under λ  ≥  420 nm, 16.05 mm  h⁻¹ under simulated sun conditions) for H₂O₂ production and 93% selectivity for 2e⁻ ORR, much higher than that of the state-of-the-art photocatalyst. The porous g-C₃N₄ with Na dopants and cyano groups simultaneously optimize two limiting steps of the photocatalytic 2e⁻ ORR: photoactivity, and selectivity. The cyano groups can adjust the band structure of g-C₃N₄ to achieve high activity. They also serve as oxygen adsorption sites, in which local charge polarization facilitates O₂ adsorption and protonation. With the aid of Na⁺, the O₂ is reduced to produce more superoxide radicals as the intermediate products for H₂O₂ synthesis. This work provides a facile approach to simultaneously tune photocatalytic activity and 2e⁻ ORR selectivity for boosting H₂O₂ production, and then paves the way for the practical application of g-C₃N₄ in environmental remediation and energy supply.     

大型水轮发电机组水导油槽漏油分析及处理工艺

目前已投产的大中型水轮发电机组的各部油槽一般都存在着不同程度的渗漏问题,这样不仅会造成资源的浪费,而且还会污染环境,甚至会严重影响到机组的安全生产。为了保证水电站机组的安全运行,考虑到造成渗漏的原因各不相同,以瀑布沟水电站3号水轮发电机组的水导油槽油位异常事件为例展开了分析研究;通过查阅相关资料和图纸,以及实际考察和运行实践,找出了水导轴承漏油的真正原因。根据漏油原因,有针对性地制定出处理措施和方法,并进行了相应处理,取得了良好的效果。     

土工膜防渗低水头平原水库渗流场及膜体稳定性

针对平原水库土工膜稳定及渗漏等问题,结合珠江三角洲某土工膜防渗平原水库实际工程,建立渗流有限元模型,模拟施工和运行过程中土工膜破损和缺陷情况,分析土工膜缺陷对库底土工膜膜体稳定性和渗漏量的影响。结果表明:平原水库库内未储水时,土工膜缺陷对平原水库渗流场和库底土工膜稳定性的影响甚微;当库内及外江水位均处于高水位时,缺陷处膜下压力水头最大,但土工膜仍可维持稳定;当土工膜缺陷距离排水盲管30m,且缺陷孔径为0.5~3.0cm时,孔径变化对缺陷处渗漏量的影响较小,但缺陷数量和位置对缺陷处总渗漏量影响显著。     

锅炉面式减温器裂纹的分析与对策

对锅炉面式减温器的损坏事故进行了分析研究,表明其损坏主要是由于面式减温器的工作温度经常发生较频繁的波动,使其经常承受热应力的作用,经过一定时间造成材质疲劳而产生裂纹.并提出相应的预防及纠正的措施.     

奥氏体不锈钢炉体应力腐蚀破裂失效分析

316L不锈钢是一种耐蚀性能很好的材料，但是安装质量特别是焊接质量对其应力腐蚀破裂(SCC)性能有很大的影响，针对抚顺石化多次沿焊接热影响区(HAZ)发生断裂事故的一套316L不锈钢设备进行失效分析，认为该设备的断裂属于SCC，焊接接头质量差是造成断裂的根本原因。     

基于Curvelet变换和支持向量机的磁瓦表面缺陷识别方法

针对磁瓦表面缺陷对比度低、自动识别困难的问题,作者提出了一种对磁瓦图像应用快速离散Curvelet变换(FDCT)提取特征,并用支持向量机(SVM)分类器进行分类的磁瓦微小缺陷自动识别方法。该方法首先对磁瓦图像做分块处理,并对各分块图像应用FDCT,计算分解系数的l2范数,获得磁瓦不同方向的纹理频域特征;然后以归一化的分解系数l2范数作为支持向量机分类器的特征向量,对图像做出分类。对不同缺陷占比的图像进行实验测试,结果显示,当缺陷部分占分块图像的比例在1/64以上时正确识别率大于83%。