Heterogeneous Bimetallic Mo-NiPx/NiSy as a Highly Efficient Electrocatalyst for Robust Overall Water Splitting

Highly efficient electrocatalysts composed of earth-abundant elements are desired for water-splitting to produce clean and renewable chemical fuel. Herein, a heteroatomic-doped multi-phase Mo-doped nickel phosphide/nickel sulfide (Mo-NiP_x/NiS_y) nanowire electrocatalyst is designed by a successive phosphorization and sulfuration method for boosting overall water splitting (both oxygen and hydrogen evolution reactions (HER)) in alkaline solution. As expected, the Mo-NiP_x/NiS_y electrode possesses low overpotentials both at low and high current densities in HER, while the Mo-NiP_x/NiS_y heterostructure exhibits high active performance with ultra-low overpotentials of 137, 182, and 250 mV at the current density of 10, 100, and 400 mA cm⁻² in 1 m KOH solution, respectively, in oxygen evolution reaction. In particular, the as-prepared Mo-NiP_x/NiS_y electrodes exhibit remarkable full water splitting performance at both low and high current densities of 10, 100, and 400 mA cm⁻² with 1.42, 1.70, and 2.36 V, respectively, which is comparable to commercial electrolysis.     

Sandwiched structure of hot-deformed Nd-Fe-B permanent magnets processed by Nd-Cu eutectic alloys diffusion

A series of sandwiched structures with different near-surface mass fractions x(x=3 wt%,4 wt%,5 wt%)was employed to develop high-coercivity hot-deformed Nd-Fe-B magnets by the addition of 2 wt%Nd-Cu eutectic alloys via adjusting the middle thickness and near-surface thickness.The designed magnet with a pronounced composite structure shows a 23% increase in coercivity with a 6% loss of remanence by adjusting the sandwiched structure at 4 wt% Nd-Cu eutectic alloys in the near-surface regions.The results indicate that the near-surface Nd-Cu-rich "shell" structure can effectively suppress the magnetization reversal of overall magnets,enhancing the coercivity.With the help of loading stress,Nd-Cu liquid enriched at the near-surface regions of the sample is infiltrated into the Nd-Cu-lean middle region,resulting in a concentration gradient.Microstructure characterizations further demonstrate that the infiltrated Nd-Cu eutectic plays a critical role in inhibiting grain growth and intergranular magnetic interaction.The optimized microstructure features suppress the reversed magnetization process,which makes a positive contribution to coercivity.     

Pressure-induced transparency of MgO,Al2O3, AlN,and cBN ceramics at room temperature

The in situ axial X-ray diffraction patterns of four ceramic powder samples (MgO, Al₂O₃, AlN, and cBN) that were compressed in a diamond anvil cell under uniaxial non-hydrostatic conditions were recorded. The microscopic deviatoric stress as a function of the pressure was determined from the X-ray diffraction peak broadening analysis: the curves increased approximately linearly with the pressure at the initial compression stage and then levelled off under further compression. Pressure-induced transparency was observed in all of the samples under compression, and the pressure at the turning point on the curves of the microscopic deviatoric stress versus pressure corresponded to the pressure at which the samples became transparent. Analysis of the microstructural features of the pressure-induced transparent samples indicated that the compression caused the grains to fracture, and the broken grains bonded with each other. We demonstrated that the ceramics’ pressure-induced transparency was a process during which the grains were squeezed and broken, the pores were close between the grains, and the broken grains were re-bonded under compression.     

Oxidation and ablation behaviour of multiphase ultra-high-temperature ceramic Ta0·5Zr0·5B2–Si–SiC protective coating for graphite

To provide reliable oxidation protection for carbon materials under harsh high-temperature aerobic environments, a dense monolayer-multiphase ultra-high-temperature ceramic Ta_0·5Zr_0·5B₂–Si–SiC (TZSS) coating was fabricated by a combination of dipping and in-situ reaction. The oxidation resistance of the TZSS coating was investigated at 1923 K in air. The results indicated that the TZSS coating could offer at least 70 h of oxidation protection for the matrix material. The synergistic oxygen-blocking effect of the thick oxide layer formed during the oxidation test and the inner coating, played a key role in the oxidation protection process. These were responsible for the excellent oxidation resistance ability of the TZSS coating. Additionally, the ablation performance of the TZSS coating was also investigated under increased heat flux from 2.4 MW/m² to 4.2 MW/m². The ablation behaviours changed from the oxidation and evaporation of coating materials to mechanical scouring, corresponding to increased mass and linear ablation rates. Interestingly, after ablation for 40 s under a heat flux of 4.2 MW/m², a new microstructure composed of “lath-like” Ta₄Zr₁₁O₃₂ solid solution grains was found in the ablation center. This oxide layer possessed few micropores, which could provide reliable protection for the matrix material under ultra-high-temperature oxygen-containing airflow erosion, thus preventing further damage to the composite.     

复合材料控制臂的多区域铺层结构优化

使用碳纤维复合材料设计某乘用车悬架控制臂,对4个区域的铺层结构进行优化设计.首先以各角度铺层厚度为设计变量对控制臂模态频率、质量和各工况应变能进行优化;然后以前三阶模态频率为目标,弯曲刚度参数作为设计变量优化铺层顺序.针对设计变量间存在的工艺约束条件使样本空间不规则且优化变量较多的问题,利用聚类分析进行试验设计确定训练近似模型需要的样本点,并用高斯过程回归方法建立近似模型以减少计算时间,验证模型R2在0.9以上.两步优化后,对比复合材料初始铺层各性能指标均有不同程度改善,复合材料质量减少11.4％;对比原钢制控制臂,各性能均满足要求,质量降低37.1％.     

Review of hydrogen crossover through the polymer electrolyte membrane

Proton exchange membrane fuel cell (PEMFC) is considered to be a promising, clean, and efficient energy conversion device. At present, the main challenges faced by the application of PEMFC in the automotive are cost and durability. Hydrogen from anode to the cathode through polymer electrolyte membrane (i.e. crossover hydrogen) affects the durability of fuel cells. In this paper, the existing literature on hydrogen crossover is reviewed and summarized from consequences, causes, mitigation measures, and detection methods. The influences of hydrogen crossover on the components and performance are discussed. The causes are analyzed from structural permeation and membrane degradation. The methods of alleviating the degradation of the membrane are summarized. The electrochemical and non-electrochemical monitoring methods are described, and the segmented current method is explained separately. The existing problems and research prospects are put forward, which lays a foundation for further research on hydrogen crossover and improvement fuel cell durability.     

Comprehending the role of the S-phase on the corrosion behavior of austenitic stainless steel exposed to H2S/CO2-saturated liquid and vapor environments

The corrosion behavior of austenitic stainless steel after low-temperature liquid oxy-nitriding (LON) was investigated by exposing in H₂S/CO₂-saturated liquid and vapor environments up to 720 h at 60 °C. The corrosion rates before and after LON were compared by the weightlessness method, and the microstructure as well as the corrosion scales were characterized using surface analysis methods. The results indicated that the composite S-phase layer with the outer Fe₃O₄ layer and the inner nitrogen-rich sublayer could improve the corrosion performance in H₂S/CO₂-saturated environment. The base material (BM) suffered local corrosion first, which then transformed into uniform corrosion. As a comparison, The LON sample, covered with a thin corrosion product layer, indicated slight local corrosion. The excellent corrosion resistance of the S-phase should be attributed to the blocking effect of the continuous Fe₃O₄ film as well as the suppression of the atomic mobility by the nitrogen-containing supersaturated solid solution.     

基于磁声电技术的肺部组织成像仿真研究

新冠肺炎可引起肺水肿和肺实变,对肺部造成严重的损害.CT检测存在辐射,超声成像对轻症患者难以发挥作用.磁声电成像是一种典型的电磁和超声相互耦合的电特性成像技术,具有高空间分辨率和高对比度的优点,可检测肺部病变早期变化.该文介绍磁声电技术的原理,利用有限元分析软件建立肺水肿或肺实变前期模型和完全肺水肿或肺实变模型,仿真分析所建模型的磁声电信号并实现了B扫成像.仿真结果表明,肺部组织内的气体对超声波有反射作用,随着肺部组织内气体含量逐渐减少,肺部组织左边界上由反射超声波形成的脉冲信号幅值减小,肺部组织右边界上由绕射过含气组织的超声波增加产生的脉冲信号幅值增大.当肺部完全水肿或肺实变后,肺部组织内不再含有气体,由反射超声波引起的脉冲信号消失,可显示内部肿块的脉冲信号.该文通过仿真论述了磁声电成像技术在新冠肺炎临床应用中的潜力.