Metal Oxide Thin Films Containing Au Nano-Particles Prepared with Gas Diffusion Method

Au particles dispersed thin metal oxide films were prepared from precursor films containing HAuCl₄ with H₂S gas diffusion method. HAuCl₄ was uniformly dissolved in the films as promoted by hydroxypropyl cellulose (HPC). The mechanism of the Au particle formation was studied. It was found that HAuCl₄ was converted directly to Au metal particles upon contacting with H₂S gas. Au particles generated by this method were characterized with small particle size, sharp size distribution and high volume fraction in the films. The surface plasma resonance absorption of Au particles shifted to longer wavelength when TiO₂ component was introduced in the matrix.     

The structure and electrochemical characteristics of La0.67Mg0.33 (Ni0.8Co0.1Mn0.1) x (x=2.5–5.0) multiphase alloys for nickel-metal hydride batteries

This paper presents results concerning structure and electrochemical characteristics of the La_0.67Mg_0.33 (Ni_0.8Co_0.1Mn_0.1) _x (x=2.5–5.0) alloy. It can be found from the result of the Rietveld analyses that the structures of the alloys change obviously with increasing x from 2.5 to 5.0. The main phase of the alloys with x=2.5–3.5 is LaMg₂Ni₉ phase with a PuNi₃-type rhombohedral structure, but the main phase of the alloys with x=4.0–5.0 is LaNi₅phase with a CaCu₅-type hexagonal structure. Furthermore, the phase ratio, lattice parameter and cell volume of the LaMg₂Ni₉phase and the LaNi₅ phase change with increasing x. The electrochemical studies show that the maximum discharge capacity increases from 214.7 mAh/g (x=2.5) to 391.1 mAh/g (x=3.5) and then decreases to 238.5 mAh/g (x=5.0). As the discharge current density is 1,200 mA/g, the high rate dischargeability (HRD) increases from 51.1% (x=2.5) to 83.7% (x=3.5) and then decreases to 71.6% (x=5.0). Moreover, the exchange current density (I ₀) of the alloy electrodes first increases and then decrease with increasing x from 2.5 to 5.0, which is consistent with the variation of the HRD. The cell volume reduces with increasing x in the alloys, which is detrimental to hydrogen diffusion and accordingly decreases the low-temperature dischargeability of the alloy electrodes.     

超临界CO2中甲醇和乙醇无限稀释扩散系数的分子动力学模拟与实验测定

采用分子动力学模拟(MD)方法对甲醇和乙醇在超临界二氧化碳中的无限稀释扩散系数进行了模拟计算, 并应用泰勒分散理论, 采用超临界色谱仪对模拟结果进行了实验验证. 模拟计算值与实验值较吻合, 且变化规律基本一致, 表明采用这种新方法可以准确有效地预测超临界体系的扩散性质, 能够方便地应用于工程设计.     

Surface modification of γ-alumina membranes by silane coupling for CO2 separation

Top layers of γ-Al₂O₃ composite membranes have been modified by the silane coupling technique using phenyltriethoxysilane for improving the separation factor of CO₂ to N₂. The separation efficiency of the modified membranes was strongly dependent upon the hydroxylation tendency of the support materials and the amount of the special functional group (i.e. phenyl radical) which was coupled onto a top layer. The separation factor through the TiO₂ supported γ-Al₂O₃ membrane was found to be fairly enhanced by silane coupling, but in case of the -Al₂O₃ supported membrane was not. The CO₂/N₂ separation factor through the modified γ-Al₂O₃/TiO₂ composite membrane is 1.7 at 90°C and ΔP = 2 × 10⁵ Pa for the binary mixture containing 50 vol% CO₂. The separation factor is proportional to the CO₂ concentration in the gas mixture, and the modified membrane is stable up to 100°C. The main mechanism of the CO₂ transport through the modified γ-Al₂O₃ layer is known to be a surface diffusion.     

氢在钯单晶表面的解离与在体相的扩散

氢分子在金属表面的解离吸附与氢原子在金属体相的扩散是个典型的表面过程.前者在甲烷化及合成氨等基础化工反应中起着关键作用;后者常常导致金属材料的脆化与断裂,但过渡金属及其合金是安全和优良的储氢材料.因此,研究氢分子在金属表面的解离吸附与氢原子在金属体相的扩散,是多相催化与金属物理广泛感兴趣的课题,具有重要的理论和应用价值.本文采用分子动力学方法初步探讨了二者之间的关联.分子催化动力学为从微观层次上研究上述课题提供了一种理论方法.本文采用经过我们改进的半经验LEPS方法,计算了氢分子在Pd(100)和(110)晶面的解离和氢原子在钯表面与体相扩散的相互作用位能面,并根据计算结果探讨了其微观机理.     

On the statistical independence of various column contributions to band broadening. Part 1: Second moment contributions from statistically independent,longitudinal diffusion in both phases

The total length-based second moment contribution from longitudinal sample diffusion in both phases on a column, σD , is derived by adding individual partial differential contributions to a partial differential equation accounting for the longitudinal diffusion processes only. Although each diffusion-dispersed sample part is equilibrated between two phases, the resulting σ,D (= 2D _mt _m + 2D _st _s) can be interpreted as the sum of two independent contributions in accordance with the variance addition rule. (D _m and D _s are the mean diffusion coefficients and t _mand t _s the mean residence times of the sample in the mobile and stationary phases, respectively.) The same σD expression is derived from the random walk model of Giddings by treating the diffusional process in each phase as statistically independent of the other processes. Under these conditions the broadening contribution from longitudinal diffusion in the mobile phase is shown to be independent of the velocity profile.     

Developments on carbon dioxide reduction: Their promise,achievements, and challenges

CO₂ reduction processes continue to be developed for electrosynthesis, energy storage applications, and environmental remediation. A number of promising materials have shown high activity and selectivity to target reduction products. However, the progress has been mainly at a small laboratory scale, and the technical challenges of large scale CO₂ reduction have not been considered adequately. This review covers recent advancements in catalyst materials and cell designs. The leading materials for CO₂ reduction to a number of useful products are presented with their corresponding cell and reactor designs. The latest efforts to progress to industrially relevant scales are discussed, along with the challenges that must be met for carbon dioxide reduction to be a viable route for mass scale production.     

染料敏化太阳能电池中大孔TiO2薄膜电极的制备及应用

采用溶胶-凝胶水热法制备了TiO₂纳晶薄膜电极，晶型为锐钛矿型。为了提高电极的光电性能，利用聚苯乙烯小球做造孔剂，制备了含有大孔隙的TiO₂纳晶薄膜电极，孔径约为200 nm，该电极具有较好的光漫反射性能，更重要的是球形大孔的存在，提高了凝胶电解质在TiO₂薄膜电极中的渗透和I₃^-离子的扩散性能，与不含大孔的TiO₂电极相比，电池的短路光电流提高约2 mA·cm^-2，光电转换效率提高0.6%。     

Grain boundary diffusion coefficients in gold–nickel thin films

Polycrystalline gold–nickel thin films are deposited on silicon (111) wafers by evaporation in a vacuum of 2 × 10^?6 mbar. Concentration profiles of heat‐treated specimens are obtained by Auger electron depth profiling. The heat treatments are carried out in a vacuum furnace of 4 × 10^?6 mbar in the temperature interval 473–773 K. The grain boundary diffusion coefficient is determined, using a modified Wipple model, to be (3 × 10^?4 cm² s^?1) exp (?0.94 eV kT^?1). It is concluded that interdiffusion in the investigated system is characterized by type B kinetics, and that grain boundary diffusion plays a dominant role in the mass transport process of such films. Copyright © 2003 John Wiley & Sons, Ltd.     

Gas diffusion-flow injection determination of total inorganic carbon in water using tungsten oxide electrode

A novel gas diffusion-flow injection method has been developed for the rapid and sensitive determination of total inorganic carbon (TIC) in water. The method is based on the diffusion of CO₂ across gas permeable membrane from a donor stream containing 0.1 M HCl to an acceptor stream of sodium acetate (10⁻⁵ mol l⁻¹ and pH 10). The CO₂ trapped in the acceptor stream passes through an electrochemical flow cell contains a tungsten oxide wire and a silver/silver chloride electrode, where it was sensitively detected. The parameters affecting the sensitivity of the electrode such as buffer concentration, pH, flow rate and injected volume were studied in detail. The electrode response was linear in the concentration range from 5 to 100 μg ml⁻¹ CO₃²⁻ with a correlation coefficient (R²) of 0.998. Precision (R.S.D.) was 1.42% for 20 μg ml⁻¹ standard solution of CO₃²⁻ (n=10). The detection limit was 0.20 μg ml⁻¹ CO₃²⁻. The method was evaluated by the injection of real natural water samples and an average recovery of 100.1% was obtained. The sampling rate was 30 samples h⁻¹. The method is simple, feasible with satisfactory accuracy and precision and thus could be used for monitoring TIC in water.