微通道内气体流动的格子Boltzmann方法研究

采用格子Boltzmann方法模拟了微通道在滑移区内不同Knudsen数下的微气体Poiseuille流,分析了微气体流动的速度分布以及流量与压降的关系,并给出了相对滑移长度和Poiseuille数随Knudsen数的变化特性。研究结果表明,微气体Poiseuille流的速度轮廓呈抛物线分布,但是边界速度大于0,出现速...     

Porous Ni@Pt core-shell nanotube array electrocatalyst with high activity and stability for methanol oxidation

Bimetallic core-shell nanostructures are emerging as more important materials than monometallic nanostructures, and have much more interesting potential applications in various fields, including catalysis and electronics. In this work, we demonstrate the facile synthesis of core-shell nanotube array catalysts consisting of Pt thin layers as the shells and Ni nanotubes as the cores. The porous Ni@Pt core-shell nanotube arrays were fabricated by ZnO nanorod-array template-assisted electrodeposition, and they represent a new class of nanostructures with a high electrochemically active surface area of 50.08 m(2) (g Pt)(-1), which is close to the value of 59.44 m(2) (g Pt)(-1) for commercial Pt/C catalysts. The porous Ni@Pt core-shell nanotube arrays also show markedly enhanced electrocatalytic activity and stability for methanol oxidation compared with the commercial Pt/C catalysts. The attractive performances exhibited by these prepared porous Ni@Pt core-shell nanotube arrays make them promising candidates as future high-performance catalysts for methanol electrooxidation. The facile method described herein is suitable for large-scale, low-cost production, and significantly lowers the Pt loading, and thus, the cost of the catalysts.     

光电催化分解水的光阳极改性策略

Photoelectrochemical water splitting is to utilize collected photo-generated carrier for direct water cleavage for hydrogen production. It is a system combining photoconversion and energy storage since converted solar energy is stored as high energy-density hydrogen gas. According to intrinsic properties and band bending situation of a photoelectrode, hydrogen tends to be released at photocathode while oxygen at photoanode. In a tandem photoelectrochemical chemical cell, current passing through one electrode must equals that through another and electrode with lower conversion rate will limit efficiency of the whole device. Therefore, it is also of research interest to look into the common strategies for enhancing the conversion rate at photoanode. Although up to 15% of solar-to-hydrogen efficiency can be estimated according to some semiconductor for solar assisted water splitting, practical conversion ability of state-of-the-art photoanode has yet to approach that theoretical limit. Five major steps happen in a full water splitting reaction at a semiconductor surface:light harvesting with electron excitations, separated electron-hole pairs transferring to two opposite ends due to band bending, electron/hole injection through semiconductor-electrolyte interface into water, recombination process and mass transfer of products/reactants. They are closely related to different proposed parameters for solar water splitting evaluation and this review will first help to give a fast glance at those evaluation parameters and then summarize on several major adopted strategies towards high-efficiency oxygen evolution at photoanode surface. Those strategies and thereby optimized evaluation parameter are shown, in order to disclose the importance of modifying different steps for a photoanode with enhanced output.     

稀土元素Sm、Eu、Gd对Nb掺杂的TiO2压敏电阻电性能的影响

研究了稀土元素Sm、Eu、Gd对于Nb掺杂的TiO₂基压敏电阻电学性能的影响. 几种稀土元素的掺杂量均为体系总量的2%(原子比), 其它原料的掺入量固定不变. 实验样品在1380 ℃烧结, 保温4 h. 实验发现, Sm、Eu、Gd等稀土元素可以有效降低TiO₂基压敏电阻的压敏电压, 但对于非线性系数的影响不很明显. 对于Sm、Eu、Gd掺杂, 实验得到的压敏电压值分别为12.7、14.7和16.1 V. 通过对试样的阻抗分析发现, Sm、Eu、Gd掺杂对于压敏电阻的介电性能有显著影响, 单独掺杂Sm或Gd的试样具有很低的介电常数和介电损耗, 并且具有很高的电阻率.     

活度系数法测定A2B型难溶盐的溶度积——以Ag2SO4为例

实验假设水溶液中Ag+和SO42－的浓度非常低时,其活度无论处于同一体系还是在不同体系均相同。依此设计原电池,使该原电池的电池反应为Ag2SO4(s)→2Ag+(aq)+SO42－(aq),采用补偿法测量一定温度下此原电池中AgNO3溶液浓度和K2SO4溶液浓度发生变化时的电池电动势E。依据能斯特方程和Debye-Huckel极限公式,推导出原电池标准电动势E?与电解质的平均活度系数γ±及溶液浓度的关系,用外推法作图得到此电池反应的标准电动势E?。由平衡常数与原电池标准电动势的关系,得到Ag2SO4的溶度积Ksp(Ag2SO4)。     

烃基硅铜酸盐与2-芳基-2-环烯酮1,4-加成反应的立体选择性及2-取代- 3-硅基环烷酮的合成

研究了烷基苯基硅铜酸盐与2-环烯酮的1,4-加成反应的立体选择性, 并合成了一系列新的2-取代-3-硅基环烷酮. 结果表明, 在0 ℃下用饱和NH₄Cl溶液处理, 烷基苯基硅铜酸盐与2-芳基-2-环烯酮的1,4-加成反应的立体选择性不同程度地受芳基和环的大小影响, 得到顺、反两种产物; 并首次发现室温下用甲醇处理反应时, 其立体选择性不受或者很少受环大小、芳基的性质以及与硅原子相连的取代基的影响, 只得到反式产物. 芳基溴甲烷与由烷基苯基硅铜酸盐与2-环烯酮1,4-加成所得的烯醇盐反应时, 只得到反式产物. 合成产物的结构用IR, ¹H NMR, ¹³C NMR, MS和HRMS等进行了表征.     

高钒掺杂量MCM-41合成及表征

采用溶胶-凝胶法,在氨性条件下合成出高钒掺杂量介孔MCM-41。以XRD,氮气吸附/脱附,透射电镜,ICP和拉曼光谱等技术对材料的结构进行了表征。结果表明当钒硅物质的量的比达到0.14时材料仍保持规整介孔结构(尽管当钒/硅物质的量的比超过0.11时开始有V₂O₅晶体出现)。所合成材料室温下在苯的过氧化氢直接羟基化反应中表现出良好的催化性能。     

In Situ Electrochemical Activation of Hydroxyl Polymer Cathode for High-Performance Aqueous Zinc–Organic Batteries

The slow reaction kinetics and structural instability of organic electrode materials limit the further performance improvement of aqueous zinc-organic batteries. Herein, we have synthesized a Z-folded hydroxyl polymer polytetrafluorohydroquinone (PTFHQ) with inert hydroxyl groups that could be partially oxidized to the active carbonyl groups through the in situ activation process and then undertake the storage/release of Zn²⁺. In the activated PTFHQ, the hydroxyl groups and S atoms enlarge the electronegativity region near the electrochemically active carbonyl groups, enhancing their electrochemical activity. Simultaneously, the residual hydroxyl groups could act as hydrophilic groups to enhance the electrolyte wettability while ensuring the stability of the polymer chain in the electrolyte. Also, the Z-folded structure of PTFHQ plays an important role in reversible binding with Zn²⁺ and fast ion diffusion. All these benefits make the activated PTFHQ exhibit a high specific capacity of 215 mAh g⁻¹ at 0.1 A g⁻¹, over 3400 stable cycles with a capacity retention of 92 %, and an outstanding rate capability of 196 mAh g⁻¹ at 20 A g⁻¹.     

F-P腔内自旋轨道耦合玻色-爱因斯坦凝聚体的色散研究

计算分析了处于单模Fabry-Pérot腔内的无相互作用玻色-爱因斯坦凝聚体在引入自旋轨道耦合作用下的色散关系. F-P腔为冷原子系统提供了量子化的光晶格,利用紧束缚近似和平均场近似进行二次量子化,选取合适的腔参数得到单原子缀饰态能级的具体表达式.两束弱的Raman激光和外加磁场作用于玻色-爱因斯坦凝聚体,实现了有效的自旋轨道耦合,提供了一个人工规范势,使玻色-爱因斯坦凝聚体中产生了沿腔轴方向一维的高度可控的狄拉克点.     

锂离子电池正极材料LiFePO4的结构与电化学性能的研究

利用固相法和球化工艺合成了橄榄石型LiFePO4粉体.该粉体由直径为10-15μm的团簇体组成.以合成材料为正极的锂离子电池的循环伏安特性表明,在循环过程中,锂离子插入和脱出具有单一的可逆机制.在不同温度下,材料的交流复阻抗谱表明,随着温度的升高,电池电化学阻抗明显减小.充放电测试结果表明,在17mA/cm2的电流密度下,材料工作电压平稳,电极极化效应较小,容量接近其理论值.在170mA/cm2的电流密度下,电池容量没有明显的减小趋势,而在170mA/cm2电流密度以上时,电池容量迅速降低,且电极极化效应比较显著.经过较大的电流密度测试后,材料在小电流密度下仍然保持着接近理论容量的循环容量.