Effect of TiMn1.5 alloying on the structure,hydrogen storage properties and electrochemical properties of LaNi3.8Co1.1Mn0.1 hydrogen storage alloys

A series of experiments were performed to investigate the effect of TiMn_1.5 alloying on the structure, hydrogen storage properties and electrochemical properties of LaNi_3.8Co_1.1Mn_0.1 hydrogen storage alloys at 303 K. For simple, A, B, and C are used to represent alloys (x = 0 wt %, x = 4 wt % and x = 8 wt %) respectively. The results of XRD and SEM show that LaNi_3.8Co_1.1Mn_0.1?xTiMn_1.5 hydrogen storage alloys have LaNi₅ phase and (NiCo)₃Ti phase. Based on the results of PCT curves, the hydrogen storage capacities of LaNi_3.8Co_1.1Mn_0.1?xTiMn_1.5 hydrogen storage alloys are about 1.28 wt % (A), 1.16 wt % (B) and 1.01 wt % (C) at 303 K. And the released pressure platform and the pressure hysteresis decrease with the increase of TiMn_1.5 content. Meanwhile the activation curves show that LaNi_3.8Co_1.1Mn_0.1?xTiMn_1.5 hydrogen storage alloy electrodes can be activated in three times and the maximum discharge capacity is 343.74 mA h/g at 303 K. In addition, with the increase of TiMn_1.5 content, the cyclic stability of the hydrogen storage alloy electrodes decreases obviously and the capacity retention decreases from 76.70% to 70.00% when TiMn_1.5 content increases from A to C. It also can be seen that LaNi_3.8Co_1.1Mn_0.1?xTiMn_1.5 hydrogen storage alloy electrode C and B have the best self-discharge ability and the best high-rate discharge ability from self-discharge curves and high-rate discharge curves.     

Structure and electrochemical hydrogen storage behaviors of alloy Co2B

The alloys Co₂B were prepared by two ways of high temperature solid phase process and arc melting, the structure of the alloys was characterized by XRD and SEM. It showed that it was structure of tetragonal Co₂B.The electrochemical experimental results demonstrated that the Co₂B prepared by two means both showed excellent cycling stability. The initial discharge capacity of Co₂B prepared by the high temperature solid phase process was 480.3 mA h g⁻¹, there was no distinct declination after 70 charge–discharge cycles and the capacity kept about 195 mA h g⁻¹. Co₂B prepared by the high temperature solid phase process showed very good electrochemical reversibility in CV curves. The hydrogen storage mechanism was also discussed, it confirmed that the high initial capacity of Co₂B prepared by the high temperature solid phase process was due to the oxidation of Co and B₂O₃, and it was irreversible.     

Formation of tetragonal hydrogen tungsten bronze by reactive mechanical alloying

Hydrogen tungsten bronzes have been synthesized by reactive mechanical alloying monoclinic tungsten (VI) oxide under hydrogen atmosphere. Two milling devices with different energy ranges were used. Regardless of the distinct reaction times, a similar phase evolution was observed with both apparatus. The characterization of the materials was performed by XRD, SEM, DSC and total hydrogen content determination. The final product obtained was a mixture of tetragonal H_0.33WO₃ and H_0.23WO₃ bronzes.     

Preparation and characterization of novel structure Co–B hydrogen storage alloy

The Co–B alloy was prepared by the chemical reduction method and the annealing method. The structural and morphological characterizations were performed using TEM and XRD. The Electrochemical Measurements were performed using LAND battery test instrument. After annealing treatment,the initial Co–B alloy decomposes to crystalline Co and B with a kind of coating sphere structure. The excellent electrochemical hydrogen storage properties are also obtained.     

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.     

Nanostructuration of CoSi by mechanical milling and mechanical alloying

CoSi is an inexpensive thermoelectric material for medium temperature (200–500 °C). Its power factor is as large as the state of the art materials; however, its thermal conductivity is too large. Then, improving its thermoelectric performances implies increasing the scattering of phonons, which can be performed by nanostructuring the material. In this paper we investigate the effect of nanostructuration on the structure, microstructure, lattice dynamics and stability of CoSi. We obtained powders of about 13 nm by mechanical milling bulk CoSi for only four hours or by mechanical alloying pure elements for twelve hours. Nanostructuration induces a 0.1% expansion of the lattice parameter. Raman spectroscopy, associated to ab initio calculations, highlights the effectiveness of nanostructuration on phonon scattering, showing a reduction of the phonon relaxation time by as much as 80%. Powders are stable up to 450 °C; then grains coarsen and a partial degradation of the material occurs, probably due to silicon sublimation. Our results indicate that nanostructuration should be considered when interested to reduce CoSi thermal conductivity.     

Preparation and electrochemical hydrogen storage of boron nitride nanotubes

Boron nitride (BN) nanotubes were synthesized through chemical vapor deposition over a wafer made by a LaNi5/B mixture and nickel powder at 1473 K. Scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were performed to characterize the microstructure and composition of BN nanotubes. It was found that the obtained BN nanotubes were straight with a diameter of 30-50 nm and a length of up to several microns. We first verify that the BN nanotubes can storage hydrogen by means of an electrochemical method, though its capacity is low at present. The hydrogen desorption of nonelectrochemical recombination in cyclic voltammograms, which is considered as the slow reaction at BN nanotubes, suggests the possible existence of strong chemisorption of hydrogen, and it may lead to the lower discharge capacity of BN nanotubes. It is tentatively concluded that the improvement of the electrocatalytic activity by surface modification with metal or alloy would enhance the electrochemical hydrogen storage capacity of BN nanotubes.     

电化学方法研究贮氢电极合金的P—C—T曲线

根据电化学和热力学的基础理论,考虑了氢气的逸度、碱液中水的活度以及碱液中水蒸汽的分压等影响因素,精确计算了金属氢化物电极反应的能斯特方程。结合三电极测试体系,建立了一套贮氢电极合金的P-C-T曲线电化学测定方法,并给出实验操作及相关参数确定的细节。该方法适用于涉及到大量实验工作的贮氢电极合金的成分优化及工艺研究。     

Structural and electrochemical properties of high-capacity Ml-Mg-Ni-based hydrogen storage alloys

The Ml-Mg-Ni-based (Ml = La-rich mixed lanthanide) hydrogen storage alloy Ml_0.88Mg_0.12Ni_3.0-Mn_0.10Co_0.55Al_0.10 was prepared by inductive melting. The micro-structure was analyzed by XRD and SEM. The alloy consists mainly of CaCu₅-type phase, Ce₂Ni₇-type phase and Pr₅Co₁₉-type phase. The electrochemical measurements show that the maximum discharge capacity is 386 mAh/g, 16.3% higher than that of the commercial AB₅-type alloy (332 mAh/g). At discharge current density of 1 100 mA/g, high rate dischargeability is 62%, while that of the AB5-type alloy is only 45%. The discharge capacity decreases to 315 mAh/g after 300 charge/ discharge cycles, 81.5% of the maximum discharge capacity. __________ Translated from Journal of Xi’an Jiao Tong University, 2008, 42(3) (in Chinese)     

Structural analysis of La-Mg-Ni-based new hydrogen storage alloy

The structural analysis of new hydrogen storage alloys, La₅Mg₂Ni₂₃ and La₃MgNi₁₄, was performed using HRTEM. As a result, these ternary system alloys were found to be mainly composed of stacked RNi₅ (CaCu₅ type) and R₂Ni₄ (Laves type) structure subunits in a superstructure arrangement. La₅Mg₂Ni₂₃ alloy is composed of the primitive cell of three LaNi₅ units and the primitive cell of two La₂Mg₂Ni₄ units. La₃MgNi₁₄ alloy is composed of four LaNi₅ and two La₂Mg₂Ni₄ unit cells.     

Structural and electrochemical properties of TiFe alloys synthesized by ball milling for hydrogen storage

The binary TiFe alloy was synthesized by mechanical alloying (MA) under argon atmosphere at room temperature. The effect of ball to powder weight ratio on the microstructures was characterized by X-ray diffraction (XRD). The effect of milling time on the electrochemical and activation properties was investigated by scanning electron microscope (SEM), galvanostatic charging and discharging, constant potential discharge, and potentiodynamic polarization techniques. Relationships between electrochemical properties, such as polarization, variation of electrochemical discharge capacity, \( \frac{D_{\mathrm{H}}}{a^2} \) ratio exchange current density, and Nernst potential and alloy compositions were evaluated. XRD results showed that with increasing ball to powder weight ratio, the amorphization process is accelerating and powders milled with a ratio of 1:8 have the highest conversion rate to TiFe. SEM observations reveal that particles show cleavage fracture morphology and size distribution is generally normalized. TiFe milled during 40 h was easily activated within 5 cycles and showed the best discharge capacity equal to 147 mAh g^?1. A good cycling was observed after 20 cycles at ambient temperature for the alloy milled for 30 h. A correlation between alloy composition, \( \frac{D_{\mathrm{H}}}{a^2} \) report, exchange current density, and Nernst potential on one hand and the variation of the electrochemical discharge capacity during cycling for different milling times on the other hand was observed.     

Study on the effect of mechanical alloying on properties of Zn-Sb alloy

The effect of mechanical alloying on Zn-Sb alloy system is investigated with X-ray diffraction (XRD), laser grain size analysis and differential scanning calorimetry (DSC) respectively. The results of laser particle size analysis shows that the particle size decreases with increasing of the grinding time between 0 and 24 h. XRD and DSC results indicate that longer the grinding time of Zn-Sb is, the more content of Zn₄Sb₃ become in the product in this process.     

Solution-phase synthesis and electrochemical hydrogen storage of ultra-long single-crystal selenium submicrotubes

Ultra-long single-crystalline trigonal selenium submicrotubes were synthesized using a facile one-step solution-phase approach with the assistance of nonionic surfactant Polyoxyethylene(20)sorbitan monolaurate (Tween-20), which turned out to be significant for the formation of ultra-long Se submicrotubes. XRD, Raman, SEM, and TEM were adopted to characterize the morphology, structure and phase composition of the as-prepared Se products. It was found that the length of the obtained Se submicrotubes was over 100 microm. By variation of the experimental parameters, the t-Se spheres, nanowires, and broken microtubes can be prepared. The possible growth mechanism of the ultra-long selenium submicrotubes was explained. In addition, we have also demonstrated that the synthesized ultra-long t-Se submicrotubes using the Tween-20-assisted approach can electrochemically charge and discharge with the high capacity of 265 mAh/g (corresponding to 0.97 wt % hydrogen in SWNTs) under normal atmosphere at room temperature. Cyclic voltammetry was adopted to investigate the adsorption-oxidation behavior of ultra-long selenium submicrotubes. It was observed that the morphology of the synthesized selenium products had a remarkable influence on their capacity of electrochemical hydrogen storage. These differences in hydrogen storage capacity are likely due to the size and density of tubes as well as the microcosmic morphology of different Se samples. The as-obtained ultra-long Se submicrotubes are expected to find wide applications in hydrogen storage, high-energy batteries, and optoelectronic, biologic, and catalytic fields as well as in the studies of structure-property relationships. This simple Tween-assisted approach might be extended to the preparations of one-dimensional nanostructures of tellurium and other anisotropic materials.     

Crystal structure and some dynamic performances of Ti0.25V0.34Dy0.01Cr0.1Ni0.3 hydrogen storage electrode

Crystal structure and some dynamic performances of Ti_0.25V_0.34Dy_0.01Cr_0.1Ni_0.3 hydrogen storage electrode alloy have been investigated by XRD,FESEM-EDS,TEM and EIS measurements.The result shows that the alloy is mainly composed of V-based solid solution phase with body-centered-cubic structure and mono-crystal Ni₃Ti phase with hexagonal structure（Space grope:P63/ nunc）,and it was first observed as TiNi-based secondary phase.The higher charge transfer resistance,higher apparent activation energy and lower hydrogen diffusion coefficient are reasons for the poor electrochemical activity of the dehydriding kinetics of Ti-V -Cr-Ni hydride alloy.     

The electrochemical performance of AB3-type hydrogen storage alloy as anode material for the nickel metal hydride accumulators

For the purpose of lowering the cost of metal hydride electrode, the La of LaY₂Ni₉ electrode was replaced by Ce. The electrochemical performances of the CeY₂Ni₉ negative electrode, at a room and different temperatures, were compared with the parent alloy LaY₂Ni₉. At room temperature during a long cycling, the evolution of the electrochemical capacity—the diffusivity indicator (\( \frac{D_{\mathrm{H}}}{a^2} \))—the exchange current density, and the equilibrium potential were determined. At different temperatures, the electrochemical characterization of this alloy allowed the estimation of the enthalpy, the entropy, and the activation energy of the hydride formation. The evolution of the high-rate dischargeability was also evaluated at different temperatures. Compared with the parent LaY₂Ni₉ alloy, CeY₂Ni₉ exhibits an easy activation and good reaction reversibility. This alloy also conserves a good lifetime during a long-term cycling. A lower activation energy determined for this alloy corresponds to an easy absorption of hydrogen into this new alloy.     

Phase structure and morphology of zinc-iron alloy electrodeposits

Zinc-iron alloy electrodeposits are providing higher corrosion resistance to steel components and also having better mechanical properties when compared to zinc deposits. This is due to the unique phase structure of the alloy formed. This study elucidates the phase structure of the electrodeposited alloy, based on the deposition kinetics and morphological characteristics. Deposition of iron was hindered by charge-transfer process, at low current densities. But zinc deposition was prevailed through diffusion control, only at high current densities. The probability of substitution of iron in hcp lattice along c-axis is more, than a-axis. This is because the linear density along c-axis is lower than a-axis. Intermetallic compounds of variable compositions were identified. Compounds such as FeZn₁₆, FeZn₁₃, Fe₅Zn₇₈ have dominantly “η” phase structure and FeZn₆, Fe₅Zn₂₂, Fe₂Zn₇, Fe₅Zn₂₉, Fe₃Zn₁₃ have “Γ” phase structure.     

Influence of preparation method on structure, morphology, and electrochemical performance of spherical Li[Ni0.5Mn0.3Co0.2]O2

Spherical Li[Ni_0.5Mn_0.3Co_0.2]O₂ was prepared by both the continuous hydroxide co-precipitation method and continuous carbonate co-precipitation method under different calcined temperatures. The physical properties and electrochemical behaviors of Li[Ni_0.5Mn_0.3Co_0.2]O₂ prepared by two methods were characterized by X-ray diffraction, scanning electron microscope, and electrochemical measurements. It has been found that different preparation methods will result in the differences in the morphology (shape, particle size, and tap density), structure stability, and the electrochemical characteristics (shape of initial charge/discharge curve, cycle stability, and rate capability) of the final product Li[Ni_0.5Mn_0.3Co_0.2]O₂. The physical and electrochemical properties of the spherical Li[Ni_0.5Mn_0.3Co_0.2]O₂ prepared by continuous hydroxide co-precipitation is apparently superior to the one prepared by continuous carbonate co-precipitation method. The optimal sample prepared by continuous hydroxide co-precipitation at 820 °C exhibits a hexagonally ordered layer structure, high special discharge capacity, good capacity retention, and excellent rate capability. It delivers high initial discharge capacity of 175.2 mAh g^?1 at 0.2 C rate between 3.0 and 4.3 V, and the capacity retention of 98.8 % can be maintained after 50 cycles. While the voltage range is broadened up to 2.5 and 4.6 V vs. Li⁺/Li, the special discharge capacities at 0.2 C, 0.5 C, 1 C, 2 C, 5 C, and 10 C rates are as high as 214.3, 205.0, 198.3, 183.3, 160.1 and 135.2 mAh g^?1, respectively.     

Preparation of Fe/B powders by mechanical alloying

Steels with a high boron content are valuable as a neutron shield in waste containers and as control absorbers in nuclear reactors. The purpose of this study was to obtain by mechanical alloying an iron powder with 50% boron (by weight) and then powder-metallurgy materials. The elementary powders were mixed in a high-energy mill for 36 h in an inert atmosphere. Samples were withdrawn at intervals, and the powder was characterized by differential thermal analysis, X-ray diffraction and electron microscopy. The Fe/B powders withdrawn at different intervals of milling were diluted with further additions of iron up to a final content of 10% boron. The mixtures were uniaxially compacted at 500 MPa; their green density was verified, and they were sintered in argon at 1150°C. Their physical properties (density and dimensional change) and bending strength were evaluated and microstructural studies and fracture tests were performed.