Effect of Ti substitution on hydrogen storage properties of Zr1−xTixCo (x = 0, 0.1, 0.2, 0.3) alloys

Zr_1−xTi_xCo (x = 0, 0.1, 0.2, 0.3) alloys were prepared by arc-melting method and the effect of Ti substitution on hydrogen storage properties was studied systematically. Hydrogen desorption pressure-composition-temperature (PCT) measurements were carried out using Sievert's type volumetric apparatus for ZrCo (at 473 K, 573 K and 673 K) and Zr_1−xTi_xCo alloys (at 673 K), respectively. Products after dehydrogenation were characterized by X-ray diffraction (XRD). In addition, the kinetics of Zr_1−xTi_xCo hydride was investigated at 473 K and 673 K, respectively, under hydrogen pressure of 5 MPa. Results showed that Ti substitution for Zr did not change the crystal structure of ZrCo phase. With the increase of temperature from 473 K to 673 K, the extent of disproportionation for ZrCo alloy increased. With Ti content increasing at 673 K, the desorption equilibrium pressure of Zr_1−xTi_xCo-H₂ systems elevated and the disproportionation reaction of Zr_1−xTi_xCo alloys was inhibited effectively. Ti substitution decreased the kinetics rate and the effective hydrogen storage capacity of Zr_1−xTi_xCo alloys slightly. Generally speaking, it was found that Zr_0.8Ti_0.2Co alloy had better anti-disproportionation property with less decrease of effective hydrogen storage capacity which was beneficial to tritium application in the International Thermonuclear Experimental Reactor (ITER).     

Untersuchungen an Hydriden im Bereich der Phase Ti2CO1—x Fe x (x=0–0,5)

The hydrogen absorption of the phase Ti₆₄Co_32–x Fe _x (x=0...16) and its influence on the magnetic properties have been investigated. Measurements of the vapour-pressure, wide-line NMR and magnetic susceptibility have been performed. Substitution of Co by Fe does not change the amount of absorbed hydrogen. However the reaction rate of hydriding process, the activation energy of diffusion and the magnetic quantities change upon this substitution.

     

Effect of Cu content on structure,hydrogen storage properties and electrode performance of LaNi4.1-x Co0.6Mn0.3Cu x alloys

The effect of Cu content on structure, hydrogen storage, and electrochemical properties of LaNi_4.1-x Co_0.6Mn_0.3Cu _x alloys has been investigated. For sample, A, B, C, and D are used to represent alloys (x?=?0, 0.15, 0.3, and 0.45), respectively. The results indicate that the four alloys are all single-phase alloy with LaNi₅ phase of CaCu₅ hexagonal structure, the hydrogen storage capacities of the alloy are about 1.49 wt% (A), 1.48 wt% (B), 1.43 wt% (C), and 1.25 wt% (D) at 303 K. With the increase of Cu content (x) from A to D, hydrogen desorption plateau pressure and pressure hysteresis decrease. Alloy electrode A shows better activation property and higher capacity (334.44 mAh/g). The addition of Cu improves the cyclic stability of the alloy electrodes when x?=?0?~?0.45. However, their self-discharge properties and high-rate dischargeability (HRD) decrease with the increase of x. Further, electrochemical kinetics and electrochemical impedance spectroscopy (EIS) analysis show that the reaction of alloy electrode is controlled by charge transfer step, and the adding of Cu benefits the electrode properties in alkaline solution.     

混合稀土对A_2B_7型储氢合金结构和电化学性能的影响

采用感应熔炼方法制备了A2B7型La0.83-0.5x(Pr0.1Nd0.1Sm0.1Gd0.2)xMg0.17Ni3.1Co0.3Al0.1(x=0~1.66)储氢合金,并在He+Ar气氛和1 173 K下进行退火处理。通过X射线衍射(XRD)、扫描电子显微镜(SEM)和电化学方法,研究了混合稀土(Pr,Nd,Sm,Gd)替代La元素对合金物相结构和电化学性能的影响。合金相结构分析表明,混合稀土含量对合金组成和相结构有重要的影响,随混合稀土含量x的增加,合金中主相A2B7型(2H-Ce2Ni7型+3R-Gd2Co7型)相丰度逐渐增多,其中2H-Ce2Ni7型相丰度先增多后减少,3RGd2Co7型相丰度则逐渐增加,主相晶胞参数随x增加而减小。电化学结果表明,随混合稀土含量增加,放氢平台压逐渐升高,合金电极的最大放电容量和循环稳定性均呈先增大后减小的规律,其中x=0.4合金电极具有最高的电化学放电容量(389.8 mAh·g-1)和最佳的循环寿命(S100=91.30%);合金电极的高倍率放电性能(HRD)则随x的增加获得显著提高。适量的混合稀土替代量可显著改善合金电极的综合电化学性能。     

Fe部分替代Cu对低钴AB_5型贮氢合金相结构和电化学性能的影响

为了获得既具有较高电化学容量又具有良好循环稳定性的低钴AB5型贮氢合金,研究了Fe部分替代Cu对低钴AB5型贮氢合金相结构和电化学性能的影响.采用真空感应熔炼方法,制备了一系列含Cu和Fe的低钴AB5型贮氢合金LaNi3.55Mn0.35Co0.20Al0.20Cu0.85-xFex(x=0.10,0.20,0.25,0.40,0.60).粉末X射线衍射(XRD)分析表明,合金含有单一CaCu5型六方结构的LaNi5相,Fe部分替代Cu并没有改变合金的本体相结构,但随着Fe含量的增大,晶格参数a,c和晶胞体积V增大.电化学性能测试表明,随着x增加,合金的放电容量和高倍率放电能力降低,但是循环稳定性得到了显著提高.当x从0.10增加到0.60时,合金的200周循环稳定性(S200)从77.6%提高到89.9%.Fe替代Cu有利于提高合金的循环稳定性,这主要是随着Fe替代量增大,晶胞体积增大,晶格体积膨胀率明显减小,合金的抗粉化能力增强.     

The Pr1-xLaxMgNi4-yCoy alloys: Synthesis,structure and hydrogenation properties

The influence of substitution Pr for La and Ni for Co on hydrogen storage properties of Pr_1-xLa_xMgNi_4-yCo_y (х = 0; 0.5, у = 0–3) alloys were studied. The existences of solid solutions have been found. It is shown that the synthesized alloys absorb hydrogen at room temperature and hydrogen pressure 0.1–10 bar. For some of the studied compounds, the formation of hydrides with cubic and orthorhombic structures was found. Hydrogen capacity for Pr_1-xLa_xMgNi_4-yCo_y alloys increases with Co content increasing and reaches 6.6 H/f.u. for PrMgNi₂Co₂. For electrochemical hydrogenation different trend was observed. With increasing of Co content discharge capacity slightly increases only to y = 0.5, and after y > 0.5, decreases. Highest discharge capacity is equal to 305 mА∙h/g for Pr_0.5La_0.5MgNi_3.5Co_0.5, and 268 mА∙h/g for PrMgNi_3.5Co_0.5 at current densities 50 mА/g and 200 mA/g, respectively. Influence of Co and number of activation cycles on HRD value of PrMgNi_4-yCo_y alloys was investigated. Additionally, obtained results of the electrochemical properties were compared with related compounds.     

Mg0.9Ti0.1Ni1－xCox (x＝0.05, 0.1, 0.15, 0.2)合金的合成及电化学性能研究

采用机械合金化法合成了Mg_0.9Ti_0.1Ni_1－xCo_x (x＝0.05, 0.1, 0.15, 0.2)系列四元合金, 并对该系列合金的结构和电化学性能等方面进行了研究. 球磨100 h的该系列合金, XRD结果表明, X射线衍射峰均呈现宽化趋势, 基本呈非晶态. 充放电结果表明, 该系列合金具有较好的活化性能, 它们的循环稳定性明显好于MgNi合金, 其中Mg_0.9Ti_0.1Ni_0.8Co_0.2最大放电容量最高, 为427.5 mAh•g^－1. 在充放电循环过程中, Mg在合金表面形成了Mg(OH)₂是合金电极衰减的主要原因. 腐蚀曲线的测试结果表明, Co的添加可以提高合金电极在碱液中的抗腐蚀能力, 从而提高了电极的循环稳定性.     

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.     

Preparation and properties of La1−xCaxCoO3 (0,2 ≤ x ≤ 0,6)

The preparatory conditions for the oxide compositions La_1?xCa_xCoO_3?δ have been determined along with their crystallographic, thermochemical, and electrical properties. Single phase solid solutions of the perovskite structure form atx < 0.6. It has been established that the compounds obtained in the open air atmosphere are oxygen deficient, the deficit increasing withx and temperature. The specific resistivity atx = 0.2–0.6 is (1–2)·10^?3 ohm·cm; it increases with the concentration of oxygen vacancies. At 0.3 ≤ x ≤ 0.6 thep-type conductivity is metallic in character with low temperature resistivity coefficients of the order (1–5)·10^?4 K^?1 in the interval 20–700°C.     

稀土元素取代对Ti0.26Zr0.07V0.24Mn0.1Ni0.33贮氢合金结构和电化学性能的影响

研究了5种稀土元素部分取代V对Ti_0.26Zr_0.07V_0..24Mn_0.1Ni_0.33合金的微观结构和电化学性能的影响。结果表明,Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33和Ti_0.26Zr_0.07V_0.24-xMn_0.1Ni_0.33RE_x（x=0.005;RE=La,Ce,Nd,Ho,Y）均由体心立方结构的钒基固溶体相和六方结构的C14Laves相组成。在合金中加入稀土元素,会使合金中两相的晶胞体积同时增大。稀土元素部分取代V均改善了合金电极的活化性能。La和Nd元素取代后,合金电极的最大放电容量明显增加,而Ce的取代提高了合金电极的循环稳定性。Ce,Nd,Ho,Y均改善了合金电极的倍率放电性能。合金电极在高温状态下表现出了良好的放电性能,其中Nd在333K时放电容量可达550.4mAh·g^-1。稀土元素对荷电保持率的影响各异。     

稀土元素取代对Ti_(0.26)Zr_(0.07)V_(0.24)Mn_(0.1)Ni_(0.33)贮氢合金结构和电化学性能的影响

研究了5种稀土元素部分取代V对Ti0.26Zr0.07V0..24Mn0.1Ni0.33合金的微观结构和电化学性能的影响。结果表明,Ti0.26Zr0.07V0.24Mn0.1Ni0.33和Ti0.26Zr0.07V0.24-xMn0.1Ni0.33REx(x=0.005;RE=La,Ce,Nd,Ho,Y)均由体心立方结构的钒基固溶体相和六方结构的C14 Laves相组成。在合金中加入稀土元素,会使合金中两相的晶胞体积同时增大。稀土元素部分取代V均改善了合金电极的活化性能。La和Nd元素取代后,合金电极的最大放电容量明显增加,而Ce的取代提高了合金电极的循环稳定性。Ce,Nd,Ho,Y均改善了合金电极的倍率放电性能。合金电极在高温状态下表现出了良好的放电性能,其中Nd在333 K时放电容量可达550.4 mAh·g-1。稀土元素对荷电保持率的影响各异。     

Surface and bulk cation distribution of the spinel system ZnxMg1−xFe2O4

Zn_xMg_1-xFe₂O₄ mixed oxide spinels (x=0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) were prepared by conventional solid state reaction method. Bulk and surface characterization of these ferrites were carried out by different techniques. The ratios Zn/Fe and Mg/Fe determined by PIXE and AAS were nearly as expected from the synthesis mixture, i.e. following the substitution model. XRD shows only a spinel structure (fcc) with increasing lattice parameter as x increases from 0 to 1. The bulk ratios of tetrahedral to octahedral sites occupied by Fe cations measured by NGR are in good agreement with the theoretical bulk stoichiometry. LEIS results indicate a Mg substitution by Fe cations at the surface. Only octahedral sites are proposed at the surface. The transition from inverse to normal spinel was follow through NGR-spectra occurring at x=0.4.     

ChemInform Abstract: Valence Changes of Manganese and Structural Phase Transitions in Sr1‐xPrxMnO3 (0.1 ≤ x ≤ 0.6).

Fifteen perovskite manganites Sr_1‐xPr_xMnO₃ with x = 0.1—0.6 in steps of 0.025 are prepared by solid state methods and their crystal structures are determined by synchrotron powder XRD.     

A Non-Hydrolytic Sol-Gel Approach for the Preparation of Mg x Al2(1−x)Ti(1+x)O5 Powders

The study of non-hydrolytic reactions for the synthesis of Mg _x Al_2(1?x)Ti_(1+x)O₅ solid solution with x = 0.6 is reported. The reagents chosen were Al(OsBu)₃, Ti(OiPr)₄, TiCl₄ and Mg(NO₃)₂·6H₂O in toluene. The reactions were followed using ¹³C Nuclear Magnetic Resonance (NMR) spectroscopy. Sol-gel synthesized powders were calcined in air at 300, 500, 1000, and 1200°C for 1 h. The powders were analysed by X-Ray Diffraction (XRD) demonstrating the formation of a Mg_0.6Al_0.8Ti_1.6O₅ phase in samples treated at the higher calcination temperature.     

Structural Aspects of Lithium Transfer in Solid Electrolytes Li2x Zn2-3xTi1+xO4 (0.33≤ x≤ 0.67)

Solid solutions Li_{2x Zn2-3x}Ti_1+xO₄, where x =1/3, 1/2, 3/5, 2/3, were studied by powder X-ray diffractometry and differential thermal analysis. Conductivity measurements have been performed in the gas phase at different temperatures and oxygen pressures. Distribution of cations over the sites of the spinel structure has been determined. Conductivity increases substantially with lithium concentration. The high lithium conductivity of Li₃Zn_0.5Ti₄O₁₀ (x=3/5) and Li₄Ti₅O₁₂ (x=2/3) is the result of two sequential phase transitions associated with different lithium distributions in high-temperature phases with defective NaCl type structures. Possible routes of lithium ion transport are discussed and rationalized based on the conductivity and crystal data.     

Crystal Structure of ϵ‐Ag7+xMg26–x – A Binary Alloy Phase of the Mackay Cluster Type

The binary alloy phase ϵ‐Ag_7+xMg_26–x with x ≈ 1 and small amounts of the β′‐AgMg phase crystallize by annealing of Ag–Mg alloys with starting compositions between 24–28 At‐% Ag at 390 to 420 °C. A model structure for the ϵ‐phase consisting of a fcc packing of Mackay clusters was derived from the known structure of the ϵ′‐Ag₁₇Mg₅₄ phase. Crystals of the ϵ‐phase were obtained by direct melting of the elements and annealing. The examination of a single crystal yielded a face‐centered cubic unit cell, space group Fm3 with a = 1761.2(5) pm. The refinement was started with the parameters of the model: wR2(all) = 0.0925 for 1093 symmetrically independent reflections. A refinement of the occupancy parameters indicated a partial replacement of silver for magnesium at two metal atom sites, resulting in the final composition ϵ‐Ag_7+xMg_26–x with x = 0.96(2). There are 264 atoms in the unit cell and the calculated density is 3.568 gcm^–3. The topology of the model was confirmed. Mackay icosahedra are located at the lattice points of a face‐centered cubic lattice. Differences between model and refined structure and their effects on the powder patterns are discussed. The new binary structure type of ϵ‐Ag_7+xMg_26–x can be described in terms of the I3‐cluster concept.     

Physicochemical and catalytic properties of La1-xCax FeO3-0.5x perovskites

The phase analysis of La_1-xCa_xFeO_3-0.5x perovskites prepared by a ceramic process from oxides is studied by X-ray diffraction and differential dissolution methods. Atx < 0.5, the system does not form a continuous series of homogeneous solid solutions and does not consist of the members of a homological series. Atx < 0.5, the system contains two phases and calcium ferrite nanoparticles located on the surface of lanthanum ferrite. Atx > 0.5, the formation of the structures of a brownmillerite-based homological series is found. The catalytic activity of perovskites depends nonmonotonically on thex value and reaches the maximum atx = 0.6.     

Darstellung und Kristallstruktur der Phasen Li26Na58Ba38Ex (E = N,H; x = 0 – 1)

Preparation and Crystal Structures of Li₂₆Na₅₈Ba₃₈E_x Phases (E = N, H; x = 0 – 1) Li₂₆Na₅₈Ba₃₈E_x (E = N, H; x = 0–1) were prepared as a majority phase by the reactions of the metals with Ba(N₃)₂ or BaH₂ at 250 °C for five days. According to single crystal and powder X‐ray diffraction investigation, all compounds are cubic, space group with the unit cell parameter a ranging from 27.335(2) (x = 0) to 27.554(3) (x = 1, E = N, H) Å and Z = 4. This compound series can be described as a filled variant of Li₁₃Na₂₉Ba₁₉, in which nitrogen or hydrogen atoms are found in the centre of Li₂₆ clusters in tetrahedral environment. Li₂₆Na₅₈Ba₃₈E_x represents a new group of metal‐rich compounds extending the growing family of subnitrides.     

Synthesis,structure and spin-crossover transition of The Cluster Compound Nb6I11−xBrx (0 ⩽ x ⩽ 2.7)

The homogeneous phase Nb₆I_11?xBr_x (0 ? x ? 2.7) is synthesized from Nb₃Br₈, Nb₃I₈ and Nb in sealed Nb capsules at 1 130 K. A second-order phase transition is found as for the composition Nb₆I₁₁ itself, changing the space group from P2₁cn (low temperatures) to Pccn, accompanied by a spin-crossover from a doublet to a quartet state. With increasing Br content the lattice constants decrease and the transition temperature shifts from 274 to 170 K while the transition interval is broadened simultaneously. Single crystal investigations for x = 0.5 and 2.3, each at 110 and 298 K, indicate a preferred substitution of one of the bridging I positions (I6) by Br atoms.     

稀土元素对Ti0.26Zr0.07V0.24Mn0.1Ni0.33贮氢合金微观结构和电化学性能的影响

本文研究了稀土元素对Ti0.26Zr0.07V0.24Mn0.1Ni0.33合金的微观结构和电化学性能的影响。结果表明,Ti0.26Zr0.07V0.24-xMn0.10Ni0.33REx(RE=Ce,Nd,Gd;x=0.01)合金均有V基固溶体相和C14型Laves相两相组成。合金中两相的晶格参数随加入稀土元素的不同而发生变化。稀土元素部分取代可改善合金电极的活化性能。然而,对合金电极的其他性能影响因元素种类不同而各异。Ce取代增大了合金电极的最大放电容量,Nd元素可以有效改善合金的高倍率放电性能。工作温度对合金电极的放电容量影响较大,Nd和Gd在333 K最大放电容量可达426和465 mAh.g-1。过高的温度使其循环容量衰减加剧。