稀土金属间化合物的催化性能——CO及不饱和气相烃在LaNi5上的加氢

本文应用脉冲色谱微型反应器研究了CO,C₂H₄,C₂H₂和C₆H₆在稀土金属间化合物LaNi₅上的催化加氢作用,并且在同一装置上与纯Ni进行了对比。实验结果表明:(1)LaNi₅的催化活性与被加氢物质的性质有关。与纯Ni相比,LaNi₅对被加氢物质所显示的催化效率按下面次序变小:CO>C₂H₄>C₂H₂>C₆H₆,但对苯而言,LaNi₅的活性却比纯Ni低。(2)在H₂中经升温处理过的LaNi₅比未经升温处理的LaNi₅具有更大的催化活性。(3)CO甲烷化反应在LaNi₅及纯Ni上均遵从一级反应速度规律,其活化能分别为15.5Kcal/mole和31Kcal/mole。     

LaNi4M(Ni,Cu,Fe)-H2体系的量热研究

本文用量热法测定了氢在LaNi₅,LaNi₄Cu,LaNi₄Fe中溶解的相对偏摩尔焓△H_Hα→β和偏摩尔自由能△G_Hα→β,并计算了偏摩尔熵△S_Hα→β。用X光衍射分析计算了LaNi₅,LaNi₄Cu,LaNi₄Fe的晶胞体积V,发现了△H_Hα→β和△G_Hα→β)与V存在线性关系。     

镧镍体系(LaNi5-xMx)吸氢化合物的研究(Ⅰ)——LaNi5的化学合成及吸氢性能

过渡金属氢化物因与氢能源的利用紧密有关,近年来在国际上引起极大注意。本文提出了吸氢化合物LaNi₅的一种新的合成方法--共沉淀还原法,并详细研究了反应过程。     

氧空位控制BiVO4晶面异质结的磁性和光电催化性能

在铁磁光催化剂中,大多数光生电荷具有相同的自旋状态,因此可以有效抑制光生电子和空穴的复合.利用BiVO₄{010}和{110}晶面中氧空位的形成能不同,通过晶面取向和氧空位的协同作用来调控BiVO₄的铁磁性能.在N2气氛中退火后,BiVO₄晶面异质结中氧空位的比例随着{010}/{110}晶面比例的增加而降低,因为{010}晶面上氧空位的形成能低于{110}晶面.{010}/{110}晶面比例较低的BiVO₄晶面异质结的铁磁性能优于{010}/{110}晶面比例较高的BiVO₄,因为前者颗粒尺寸更小、更立体,其比表面积和界面区域更大,所以其表面未饱和自旋对总磁矩的贡献更大.{010}/{110}比例较高的BiVO₄晶面异质结具有更大的光电流密度和光电催化产氢效率,源于BiVO₄{010}晶面比{110}晶面具有更高的电荷迁移率、更好的吸附特性和更低的能垒.并且氧空位的引入也提高了BiVO₄的制氢效率.     

熔铁催化剂还原过程的原位XRD研究及活性相的形成机理

选择Fe1-xO基和Fe3O4基氨合成熔铁催化剂ZA-5和A110, 采用XRD原位反应器模拟真实的还原条件进行原位XRD实验. 通过对还原过程的物相跟踪分析和对前驱体、活性相的XRD微结构动态演化分析表明, ZA-5和A110的还原温度区间分别为300~362 ℃和343~450 ℃, 前者比后者具有更快的还原速度及更低的还原温度; ZA-5和A110在(211)和(110)方向的晶粒度比值(D₍₂₁₁₎/D₍₁₁₀₎)分别为0.7014和0.8631, ZA-5催化剂具有更好的高活性(211)晶面, 其活性相微观应力明显比A110大, 且随着温度升高逐渐减小; 采用Rietveld全谱拟合结构分析和Popa模拟技术对活性相晶形进行模拟, 得到A110活性相晶形为凹陷立方体, ZA-5为立方体和球形的混合晶形, ZA-5的高活性晶面(111)和(211)晶面比A110生长更好; ZA-5催化剂活性相晶形从低温的类八面体向高温球形演化, 在355 ℃时有比较完善的八面体晶形, 此温度下(111)晶面生长得最好; ZA-5催化剂活性相与前驱体的八面体晶形结构匹配性好, 比A110更容易还原.     

LiCl-KCl-LaCl3熔盐体系中La(III)的电化学行为

在773 K条件下,研究了La（III）在LiCl-KCl熔盐中W和Ni电极上的电化学行为。La（III）还原反应是一步三电子转移的准可逆反应;通过在Ni电极上直接电沉积La的方法可以获得La-Ni金属间化合物;恒电位电解可以获得含三种金属间化合物（LaNi₅、La₇Ni₁₆和La₂Ni₃）的La-Ni合金层,并且通过X射线衍射仪（XRD）和扫描电镜-能谱分析仪（SEM-EDS）确定物相并表征结构。采用开路计时电位法估算了LaNi₅金属间化合物的标准生成吉布斯自由能。揭示了恒电位电解方法是制备La-Ni镀层合金以及提取熔盐中La的有效方法。     

镧镍铜钴储氢合金的制备与性质

以LaNi₅为代表的镧系储氢合金有优良的吸放氢性能,抗中毒能力强,因而受到广泛重视^[1]. 目前已开发出许多二元及多元镧系合金,并研究了部分合金的表面性质^[1～4],但结果并不一致. 本文制备了四元合金LaNi₄Cu_0.5Co_0.5,通过X 射线光电子能谱(XPS)、扫描电镜(SEM)和吸氢测试等方法研究该合金的性质。     

CePO4低指数晶面结构性质的密度泛函理论研究

采用密度泛函理论系统研究了CePO₄三个低指数晶面的几何结构、原子弛豫和表面能。通过观察表面结构以及比较表面能大小得出最优晶面。结果表明：表面原子均存在不同程度的弛豫,表面原子弛豫程度导致表面能的差异。表面能的大小顺序为(010)<(100)<(001),(010)晶面是CePO₄晶体稳定表面。稳定表面几何结构表明,终止末端暴露原子为O原子。使用Wulff结构计算的平衡形态表明(001)晶面、(010)晶面和(100)晶面面积分别占总晶体形状面积的14%,45%和41%。低能表面在Wulff结构中起主导作用,表面能越低的晶面面积占比越大。稳定的CePO₄晶面存在不饱和键,有利于气体分子的吸附。这项工作对CePO₄在其他方面的密度泛函理论(DFT)研究具有指导性意义,并将为CePO₄基催化剂上的吸附和解离提供稳定表面。     

具有主导晶面的BiOIO3/BiOCl异质结制备与光催化性能

分别以乙二醇/去离子水为溶剂,通过溶剂热/水热法分别制备了具有不同主导晶面的BiOIO₃/{110}BiOCl和BiOIO₃/{001}BiOCl异质结。采用X射线衍射、扫描电子显微镜、能量色散谱和紫外可见漫反射光谱对制备的BiOIO₃/BiOCl光催化剂进行了表征。在可见光照射下,通过对罗丹明B和苯酚水溶液的光催化降解,考察了BiOIO₃/BiOCl异质结的光催化活性。结果显示25%BiOIO₃/{110}BiOCl异质结具有最高的光催化效率。BiOIO₃/{110}BiOCl较好的光催化性能是由于其在可见光区较强的光吸收,以及异质结结构和BiOCl所具有的(110)主导晶面有利于光生载流子的分离。超氧自由基(·O₂^-)和空穴(h⁺)是光催化过程中的主要活性物质。此外,根据实验结果探讨了光催化性能增强的机理。     

{110}晶面取向Ag3PO4多面体的水热制备及可见光催化活性

采用简易水热法在聚乙二醇-6000 (PEG-6000)辅助下合成了Ag₃PO₄多面体.系统考察了水热反应温度、时间及PEG-6000用量对产物形貌和结构的影响.通过X射线衍射(XRD),扫描电子显微镜(SEM),紫外-可见漫反射光谱(UV-Vis DRS)和荧光(PL)光谱等测试手段对光催化剂进行了表征.结果表明,适宜的水热温度及PEG-6000用量是制备具有{110}活性晶面取向Ag₃PO₄多面体的必要条件,该多面体通过纳米颗粒的Ostwald熟化效应生长而成.可见光催化降解罗丹明B (RhB)的实验表明,该Ag₃PO₄多面体活性明显优于其它水热条件下所制备的非{110}取向晶面样品和离子交换法所得纳米颗粒,其降解反应速率常数(k)为离子交换法所得Ag₃PO₄纳米颗粒的8.3倍.总有机碳含量(TOC)及循环实验证明,该Ag₃PO₄多面体可以有效地矿化RhB并保持较好的循环稳定性.活性自由基捕获实验表明,空穴(h⁺)和羟基自由基(·OH)是光催化氧化的主要活性物种.结合活性物种的氧化还原电位以及Ag₃PO₄的能带结构分析,提出了催化反应界面光生电子-空穴(e^--h⁺)对的分离及转移机制.     

LaNi4Co晶体及电子结构的理论分析

根据密度泛函理论,采用总体能量计算方法,以扩展平面波函数为基集,并结合超软赝势技术,对LaNi5的不同Ni位分别被Co取代后的晶体几何结构进行了优化,从理论上给出了其结构参数及性质。计算结果表明,该方法能较好地符合LaNi4Co晶体结构的实验值,为该类合金的结构预测提供了理论依据。计算了LaNi4Co的总体能量、电子态密度以及Mulliken布居电荷。根据计算结果,分析了LaNi4Co的电子结构,及Co取代前后合金中电子结构的变化,比较了Co分别位于Ni的2c和3g位时的稳定性。分别从晶体结构、能量和电子结构的角度分析了Co取代时影响合金稳定性的因素。给出了LaNi4Co的生成热的理论计算值。     

铝和硅元素掺杂对LaNi5电子结构影响的研究

采用第一原理离散变分法（DVM）研究了常用元素Al和Si掺杂对稀土系贮氢合金LaNi5电子结构的影响，在计算结果的基础上进一步探讨了微观结构对合金宏观性能的影响。分析结果表明：进入八面体间隙的H原子主要与LaNi5合金中非氢化物形成元素M和Ni发生较强的相互作用．而H原子与合金中的氢化物形成元素La的相互作用很弱。同时Al和Si两种掺杂元素对LaNi5合金性能的影响基本相似。     

Density Functional Theory Calculations Revealing Metal‐like Band Structures and Work Function Variation for Ultrathin Gallium Arsenide (111) Surface Layers

Density functional theory (DFT) calculations have been performed on tunable numbers of gallium arsenide (100), (110), and (111) planes for their electron density of states (DOS) plots and the corresponding band diagrams. The GaAs (100) and (110) planes show the same semiconducting band structure with tunable plane layers and a band gap of 1.35 eV around the Fermi level. In contrast, metal‐like band structures are obtained with a continuous band structure around the Fermi level for 1, 2, 4, 5, 7, and 8 layers of GaAs (111) planes. For 3, 6, and 9 GaAs (111) planes, the same semiconducting band structure as seen in the (100) and (110) planes returns. The results suggest the GaAs {111} face should be more electrically conductive than its {100} and {110} faces, due to the merged conduction band and valence band. GaAs (100) and (110) planes give a fixed work function, but the (111) planes have variable work function values that are smaller than that obtained for the (100) and (110) planes. Furthermore, bond length, bond geometry, and frontier orbital electron number and energy distribution show notable differences between the metal‐like and semiconducting plane cases, so the emergence of plane‐dependent electronic properties have quantum mechanical origin at the orbital level. GaAs should possess similar facet‐dependent electronic properties to those of Si and Ge.     

LaNi5合金的吸氢动力学

研究了LaNi_5-H体系的吸氢反应动力学。在吸放氢可逆反应同时考虑的情况下, 求得了速度方程的解析解。在α相区20—50 ℃的温度范围内, 吸氢速度常数k_α为0.08—0.41 s~(-1); 脱氢速度常数k_d为4.8—25 MPa·s~(-1)。吸氢反应的表观活化能E_α为35 kJ(mol H_2)~(-1)。在α+β相区的吸氢较α相区慢得多。起始阶段吸氢速度对氢压为一级, 反应受氢化物表面上氢分子解离控制。随着吸氢反应深度的增大, 吸氢速度变为固相中的界面反应控制。速度常数受温度的影响很小。α+β相区的压力平台前半段和后半段有着不同的吸氢速度。     

Analysis of surface anchored lattice plane orientation in blue phase liquid crystal and its in-plane electric field-dependent capacitance response

Uniformly oriented macroscopic monodomain of cholesteric blue phase liquid crystal has been realised by the influence of surface anchoring. Orientation of the lattice planes in surface-treated (ST) and non-surface-treated (NST) cell were analysed and compared by Kossel diagram technique. NST cell has revealed the green and blue domains corresponding to reflection from oriented (110) and (112) planes of the body-centred cubic lattice. However, in the ST cell only the lattice plane (110) oriented uniformly and tailored the macroscopic monodomain. Electric field driven reorientation of the (110) lattice plane was noticed in NST cell whereas for ST cell such reorientation was absent. Two distinct electric field-induced capacitive responses have been observed in the two different cells. In NST cell anomalous electrostriction was observed, whereas for ST cell normal electrostriction was observed. Interestingly, the capacitance has decreased with an increasing electric field for anomalous electrostriction in NST cell, whereas for normal electrostriction in ST cell it was increased with increasing the field. Such a capacitive change behaviour is explained by dielectric anisotropic change followed by the electric field induced elongation and contraction of the cubic unit cell along and perpendicular to the electric field.     

Epitaxial growth and electrochemical properties of Li4Ti5O12 thin-film lithium battery anodes

Epitaxial Li(4)Ti(5)O(12) thin-films were successfully synthesized on SrTiO(3) single-crystal substrates with (111), (110), and (100) lattice plane orientations using pulsed laser deposition (PLD). Thin-film X-ray diffraction (XRD) revealed that the Li(4)Ti(5)O(12) films had the same orientation as the SrTiO(3) substrates: Li(4)Ti(5)O(12) (111) on SrTiO(3) (111), Li(4)Ti(5)O(12) (110) on SrTiO(3) (110), and Li(4)Ti(5)O(12) (100) on SrTiO(3) (100). These epitaxial films contained island structures, and the morphology of the (111), (110), and (100) films, observed by field emission scanning electron microscopy (FE-SEM), exhibited angular, needle-like, and circular shapes, respectively. The electrochemical properties of 20 nm thick Li(4)Ti(5)O(12) (111) and (110) films were investigated by cyclic voltammetry. Reversible intercalation proceeded through both lattice planes due to the three-dimensional diffusion pathway of lithium in the spinel framework. Reduction peaks in the first cathodic scan appeared at different positions from those in subsequent scans, suggesting a surface reconstruction at the Li(4)Ti(5)O(12) surface due to interfacial reactions.     

Automated search for new thermoelectric materials: the case of LiZnSb

An automated band structure calculation based on the inorganic crystal structure database and the augmented plane wave method for electronic structure calculations is presented. Using a rigid band approach and semiclassic Boltzmann theory the band structures are analyzed and a large number of compounds are screened for potential interesting thermoelectric properties. We thereby propose LiZnSb as a potential new thermoelectric material. The k-space structure of the lowest conduction band of LiZnSb is analyzed in detail, and excellent thermoelectric properties are expected for this material. Furthermore the lattice dynamics are calculated, and anisotropic lattice thermal conduction is predicted.     

First-principle electronic, elastic, and optical study of cubic gallium nitride

The ab initio pseudopotential (PP) method within the generalized gradient approximation (GGA) has been used to investigate the electronic, elastic constants, and optical properties of zinc-blende GaN. An underestimated band gap along with higher DOS and squeezed energy bands around the fermi level is obtained. The d-band effect is briefly discussed for electronic band structure calculations. With the help of elastic constants, acoustic wave speeds are calculated in [100], [110], and [111] planes. The dielectric constant, refractive index, and its pressure coefficient are well illustrated. The effect of hydrostatic pressure is explicated for all these properties. The results of the present study are evaluated with the existing experimental and first-principle calculations.     

Electrochemistry of platinum single crystal surfaces: Part II. Structural effect on formic acid oxidation and poison formation on Pt (111), (100) and (110)

The geometrical arrangement of sites favourable for formic acid oxidation and the poison formation reaction is determined using low index platinum single crystal planes. For this determination, the least number of sites required for the reactions to occur, which was obtained in the study of electrocatalysis by adatoms, was used, that is three adjacent sites are required for formic acid oxidation and four adjacent sites are required for poison formation.The triplet of sites on a unit lattice of Pt (111) and that on a unit lattice of Pt (100) plane are equally very favourable for the main oxidation reaction, but that on a unit lattice of Pt (110) is not so favourable as those on the former two planes. The oxidation rate is more than one order of magnitude lower on the latter than on the former triplets.The poison formation reaction proceeds at a very high rate on the (100) and the (110) planes. The geometrical arrangement of four sites on a square unit lattice of the (100) plane and on a rectangular unit lattice of the (110) plane are favourable for the poison formation reaction, but that on a hexagonal unit lattice of the (111) plane is not so favourable as the former two.     

A comparative study of hydroxide adsorption on the (111), (110), and (100) faces of silver with cyclic voltammetry, ex situ electron diffraction, and in situ second harmonic generation

Hydroxide adsorption on the (111), (110), and (100) faces of silver electrodes from mixed NaOH/NaF solution is studied using cyclic voltammetry and in situ second harmonic generation (SHG). Cyclic voltammograms for the three low index silver planes in alkaline electrolytes are for the first time compared. They show two pairs of anodic and cathodic peaks in the potential interval below the equilibrium Ag/Ag(2)O potential. These are attributed to the specific adsorption of hydroxide ions followed by submonolayer oxide formation. The differences in the cyclic voltammograms for the (111), (110), and (100) planes are attributed to different (i) work functions, (ii) surface atomic densities, and (iii) corrugation potentials for these surfaces. Ex situ low energy electron diffraction (LEED) and reflection high energy electron diffraction (RHEED) show that disordered adlayers are formed on Ag(111) and Ag(100), in contrast to Ag(110), where ordered structures are produced in the region of the first pair of current peaks. In the region of the second pair of peaks, LEED indicates disordered oxide phases on each crystal plane and RHEED shows the presence of small islands of c(2 x 2) structure at some potentials on (110) and (100). SHG measurements were performed (i) in the potential scan mode at constant rotational angle and (ii) at constant potential as a function of the rotational angle. The isotropic (for the (111), (110), and (100) planes) and anisotropic (for the (110) and (111) planes) contributions to the SHG intensity were calculated by fitting the experimental data and are discussed in terms of their dependence on the charge density at the interface, on hydroxide adsorption, and on submonolayer oxide formation.