Multilayer Si@SiOx@void@C anode materials synthesized via simultaneously carbonization and redox for Li-ion batteries

In the development of high-performance lithium-ion batteries (LIBs), the composition and structure of electrode materials are of critical importance. Silicon has a theoretical specific capacity 10 times that of graphite, nonetheless, its application as an anode material confronts challenge as it undergoes huge volume change and pulverization amidst the alloying and dealloying processes. Herein, a novel method to prepare a multilayer Si-based anode was proposed. Three layers, SiO₂, nickel and triethylene glycol (TEG), were coated successively on Si nanoparticles, which served respectively as the sources of SiO_x, sacrificial templates and carbon. Nickel can not only serve as a hollow template, but also play a catalytic role, which makes carbonization and redox reactions occur synchronously under a mild condition. Amid the carbonization process of TEG at 450 °C, several-nm-thick SiO₂ layer can react with the as-derived carbon to form a silicon suboxides (SiO_x (0 < x < 2)) intermedium layer. After removing the nickel template, a micro-nano scaled Si@SiO_x@void@C with conformal multilayer-structure can be obtained. The BET specific surface area and pore volume of powders were increased dramatically because of the derivation of abundant voids, which can not only buffer the swelling effect of silicon, but also provide richer ionic conductivity. The as-assembled half-cell with Si@SiOx@void@C as the anode material possesses high capacity (～1000 mAh g^?1 at 3 A g^?1), long cycle life (300 cycles with 77% capacity retention) and good rate performance (558 mAh g^?1 at 5 A g^?1).     

Highly electrocatalytic activity Ruddlesden−Popper type electrode materials for solid oxide fuel cells

To promote the viability of commercial solid oxide fuel cell (SOFC), developing novel oxygen electrodes with high electrochemical activity is essential. Herein, a series Ruddlesden-Popper oxides, Sr_3?xLa_xFe₂O_7?δ (SLFx), are successfully synthesized and evaluated as potential cathode materials for SOFC. The oxygen desorption behavior, electrochemical activity and oxygen reduction reaction (ORR) kinetics of the SLFx cathodes are systematically discussed. The Sr_2.9La_0.1Fe₂O_7?δ (SLF10) cathode exhibits highest oxygen vacancy concentration and excellent electrocatalytic performance, as evidenced by a low polarization resistance of 0.14 Ω cm² and high maximum power density of 0.77 W cm^?2 at 700 °C. From electrochemical impedance spectra and distribution of relaxation times analysis, the oxygen adsorption/desorption process is the rate-limiting step toward ORR at the cathode interface. Furthermore, SLF10 shows considerable polarization overpotentials in both SOFC and solid oxide electrolysis cell (SOEC) modes, indicating that SLF10 is a promising bifunctional electrode for electrocatalytic oxygen reaction.     

Porous TiO2/rGO nanocomposites prepared by cold sintering as efficient electrocatalyst for nitrogen reduction reaction under ambient conditions

Haber–Bosch process as the current dominant artificial NH₃ production process in industry, requires relatively high temperature (350–550 °C) and pressure (150–350 atm). Electrocatalytic nitrogen reduction reaction (NRR) as a green and sustainable strategy for ammonia production has raised intensive research interest in recent years but still remains a significant challenge because of the lack of high performance electrocatalysts. In this work, porous TiO₂-reduced graphene oxide (TiO₂/rGO) nanocomposite as self-supporting efficient electrocatalyst for NRR under ambient conditions were prepared by cold sintering associated with sacrificial template method. The porous TiO₂/rGO nanocomposite with grain size of ～40 nm were prepared by cold sintering process at 220 °C and 147 MPa. Given the 220 °C as cold sintering temperature, anatase TiO₂ were preserved as the final phase which exhibit much better NRR electrocatalytic performance than the rutile phase. The oxygen vacancy densities in the nanocomposites were also tuned by heat treatment at 450 °C under different atmosphere, while samples heat treated under H₂/Ar atmosphere gave the best electrocatalytic NRR performance with a FE of 8.88 % and an NH₃ yield of 7.75 μg h^?1 cm^?2 at ambient conditions. Experiments also shows that the addition of rGO significantly improved the electrocatalytic NRR performance especially the conductivity. This work not only designed a framework of ceramic nanocomposites based self-supporting and durable electrocatalysts system but also paves a feasible way towards preparing electrocatalysts that are sensitive to high temperature fabrication process.     

In situ synthesis of Al2O3–SiC powders via molten-salt-assisted aluminum/carbothermal reduction method

Al₂O₃–SiC composite powder (ASCP) was successfully synthesized using a novel molten-salt-assisted aluminum/carbothermal reduction (MS-ACTR) method with silica fume, aluminum powder, and carbon black as raw materials; NaCl–KCl was used as the molten salt medium. The effects of the synthesis temperature and salt-reactant ratio on the phase composition and microstructure were investigated. The results showed that the Al₂O₃–SiC content increased with an increase in molten salt temperature, and the salt–reactant ratio in the range of 1.5:1–2.5:1 had an impact on the fabrication of ASCP. The optimum condition for synthesizing ASCP from NaCl–KCl molten salt consisted of maintaining the temperature at 1573 K for 4 h. The chemical reaction thermodynamics and growth mechanism indicate that the molten salt plays an important role in the formation of SiC whiskers by following the vapor-solid growth mode in the MS-ACTR treatment. This study demonstrates that the addition of molten salt as a reaction medium is a promising approach for synthesizing high-melting-point composite powders at low temperatures.     

Promotional effect for SCR of NO with CO over MnOx-doped Fe3O4 nanoparticles derived from metal-organic frameworks

MnO_x-Fe₃O₄ nanomaterials were fabricated by using the innovative scheme of pyrolyzing manganese-doped iron-based metal organic framework in inert atmosphere and exhibited extraordinary performance of NO reduction by CO (CO-SCR). Multi-technology characterizations were conducted to ascertain the properties of fabricated materials (e.g., TGA, XRD, SEM, FT-IR, XPS, BET, H₂-TPR and O₂-TPD). Moreover, the interaction between reactants and catalysts was ascertained by in situ FT-IR. Experimental results demonstrated that Mn was an ideal promoter for iron oxides, resulting in decrease of crystallite size, improve reducibility property, enhance the mobility and the amount of lattice O^2- species, as well as strength the adsorption ability of active NO and CO to form multiple species (e.g., nitrate and carbonate). The unprecedented enhancement of CO-SCR activity over Mn-Fe nanomaterials follows the Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) reaction pathway.     

减阻聚合物薄膜的研制

表面修形技术,可以减少飞机阻力而不改变飞机结构,应用方便,维护简单,颇有吸引力。国外70年代开始进行该技术的研究,大多数研究者利用Riblets(它是一些具有顺流向开槽的平面,而沟槽面的形状通常为三角形,沟槽深为几个微米)来减小紊流附面层阻力[1].美国3M公司制造的自粘接Riblets     

汽车转向系减振器减摆效果仿真计算分析

采用仿真计算方法,对汽车转向系液压阻尼减振器消减一种国产微型汽车独立悬架转向轮摆振的效果进行了分析。建立了该车转向系的五自由度集总参数摆振分析模型,并确定了模型的各种参数;应用数值方法求解系统摆振运动微分方程组,进行了多种情况的摆振仿真计算分析,得出了关于采用阻尼减振器控制转向轮摆振的几点重要结论。     

矩形管道内高分子减阻液的减阻特性

在设计较高稳定度矩形管道流动系统和可控人工扰动设备基础上,通过有效地率定管道断面尺寸,对高聚物(PAM)减阻液的减阻特性,特别是反应点和极限减阻线进行实验研究,为以“聚合物层流”存在为基础的减阻机理假说,提供矩形管道内的实验证据及实验基础.     

Graph-Based Dimensionality Reduction for Hyperspectral Imagery: A Review

Hyperspectral image(HSI) contains a wealth of spectral information, which makes fine classification of ground objects possible. In the meanwhile, overly redundant information in HSI brings many challenges. Specifically, the lack of training samples and the high computational cost are the inevitable obstacles in the design of classifier. In order to solve these problems, dimensionality reduction is usually adopted. Recently, graph-based dimensionality reduction has become a hot topic. In this paper, the graph-based methods for HSI dimensionality reduction are summarized from the following aspects. 1) The traditional graph-based methods employ Euclidean distance to explore the local information of samples in spectral feature space. 2) The dimensionality-reduction methods based on sparse or collaborative representation regard the sparse or collaborative coefficients as graph weights to effectively reduce reconstruction errors and represent most important information of HSI in the dictionary. 3) Improved methods based on sparse or collaborative graph have made great progress by considering global low-rank information, local intra-class information and spatial information. In order to compare typical techniques, three real HSI datasets were used to carry out relevant experiments, and then the experimental results were analysed and discussed.Finally, the future development of this research field is prospected.