Microstructure and some dynamic performances of Ti0.17Zr0.08V0.34RE0.01Cr0.1Ni0.3 (RE = Ce, Dy) hydrogen storage electrode alloys

Microstructure and some dynamic performances of Ti0.17Zr0.08V0.34RE0.01Cr0.1Ni0.3 (RE=Ce, Dy) hydrogen storage electrode alloys have been investigated using XRD, FESEM-EDS, ICP-MS and EIS measurements. The alloy is composed of V-based solid solution phase with a dendritic shape and a continuous C14 Laves phase with a network shape surrounding the dendrite. Pressure-composition isotherm curves indicate that the alloy with Dy addition has a lower equilibrium hydrogen pressure and a wider plateau region. The alloy electrode with Dy addition has higher discharge capacity, while the alloy electrode with Ce addition has better activation and higher cycle stability. The alloy electrode with Ce addition has better electrochemical activity with higher exchange current density (127.5 mA g(-1)), lower charge transfer resistance (1.37 Omega) and lower apparent activation energy (30.5 kJ mol(-1)). The capacity degradation behavior for the alloy electrode is attributed to two main factors: one is the dissolutions of V and Zr element to KOH solution, and another is the larger charge transfer resistance which increases with increasing cycle number.

Effect of cerium on microstructure and electrochemical performance of Ti-V-Cr-Ni electrode alloy

Effect of cerium on the microstructure and electrochemical performance of the Ti0.25V0.35-xCexCr0.1Ni0.3 (x = 0, 0.005) electrode alloy was investigated by X-ray diffraction (XRD), field emission scanning electron microscopy/energy dispersive X-ray spectrometry (FESEM-EDS), and electrochemical impedance spectroscopy (EIS) measurements. On the basis of XRD and FESEM-EDS analysis, the alloy was mainly composed of V-based solid solution with body-centered-cubic structure and TiNi-based secondary phase. Ce did not exist in two phases, instead, it existed as Ce-rich small white particles, with irregular edges, distributed near the grain boundaries of the V-based solid solution phase. Discharge capacity, cycle stability, and high-rate discharge ability of the alloy electrode were effectively improved with the addition of Ce at 293 K. It was very surprising that the charge retention was abnormal with larger discharge capacity after standing at the open circuit for 24 h. EIS indicated that addition of Ce improved the dynamic performance, which caused the charge transfer resistance (R-T) to decrease and exchange current density (I-0) to increase markedly. The exchange current density of the electrochemical reaction on the alloy surface with Ce addition was about 2.07 and 3.10 times larger than that of the alloy without Ce at 303 and 343 K, respectively.

Crystallographic and electrochemical characteristics of La0.7Mg0.3Ni3.5-x (Al0.5Mo0.5)(x) (x=0-0.8) hydrogen storage alloys

The crystal structure, hydrogen storage property and electrochemical characteristics of the La0.7Mg0.3Ni3.5-x(Al0.5Mo0.5), (x=0-0.8) alloys have been investigated systematically. It can be found that with X-ray powder diffraction and Rietveld analysis the alloys are of multiphase alloy and consisted of impurity LaNi phase and two main crystallographic phases, namely the La(La, Mg)(2)Ni-9 phase and the LaNi5 phase, and the lattice parameter and the cell volume of both the La(La, Mg)(2)Ni-9 phase and the LaNi5 phase increases with increasing A] and Mo content in the alloys. The P-C isotherms curves indicate that the hydrogen storage capacity of the alloy first increases and then decreases with increasing x, and the equilibrium pressure decreases with increasing x. The electrochemical measurements show that the maximum discharge capacity first increases from 354.2 (v = 0) to 397.6 mAh g(-1) (x = 0.6) and then decreases to 370.4 mAh g(-1) (x= 0.8). The high-rate dischargeability of the alloy electrode increases lineally from 55.7% (x=0) to 73.8% (x=0.8) at the discharge current density of 1200 mA g(-1). Moreover, the exchange current density of the alloy electrodes also increases monotonously with increasing x.

Kinetic and electrochemical properties of icosahedral quasicrystalline Ti45Zr35Ni17Cu3 powder

Kinetic and electrochemical properties of icosahedral quasicrystalline Ti45Zr35Ni17Cu3 alloy powder as negative electrode material of Ni-MH battery have been investigated at different temperatures. The calculated results show that the apparent activation enthalpy of the charge-transfer reaction is 43.89 kJ mol(-1), and the activation energy of hydrogen diffusion is 21.03 kJ mol(-1). The exchange current density and the diffusion coefficient of hydrogen in the bulky electrode increase with increasing temperature, indicating that increasing temperature is beneficial to charge-transfer reaction and hydrogen diffusion. As a result, the maximum discharge capacity, activation property and high-rate dischargeability are greatly improved with increasing temperature. However, the charge retention and the cycling stability degrade with the increase of the temperature.

Electrochemical properties of Ti0.17Zr0.08V0.35Cr0.10Ni0.30 alloy electrode

The electrochemical properties of the Ti0.17Zr0.08V0.35Cr0.10Ni0.30 alloy electrode were investigated. This alloy has good cycle life at 303 K, 313 K, and even at 323 K, but the discharge capacity decreases gradually at 333 K with increasing cycle number. Both the charge-discharge efficiency and the charge-discharge voltage reduce. The electrochemical impendence spectra indicate that the charge-transfer resistance decreases while the exchange current density increases as temperature increases. The apparent activation energy of the charge-transfer reaction is about 50 kJ mol(-1), which is higher than that on the AB(5) type alloy electrode.

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 La0.67Mg0.33 (Ni0.8Co0.1Mn0.1) (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 LaNi(5)phase with a CaCu5-type hexagonal structure. Furthermore, the phase ratio, lattice parameter and cell volume of the LaMg2Ni9 phase 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.

Interplay between s-d exchange interaction and Rashba effect: Spin-polarized transport

The authors investigate the spin-polarized transport properties of a two-dimensional electron gas in a n-type diluted magnetic narrow gap semiconductor quantum well subjected to perpendicular magnetic and electric fields. Interesting beating patterns in the magnetoresistance are found which can be tuned significantly by varying the electric field. A resonant enhancement of spin-polarized current is found which is induced by the competition between the s-d exchange interaction and the Rashba effect [Y. A. Bychkov and E. I. Rashba, J. Phys. C 17, 6039 (1984)]. (c) 2006 American Institute of Physics.

Influence of catalyst layer structure on the current distribution of PEMFCs

A modified subcell approach was adopted to evaluate the current density distributions of proton exchange membrane fuel cells (PEMFCs) with different electrodes. Conventional hydrophobic electrodes showed better performance under flooding conditions compared to hydrophilic electrodes. The thin-film hydrophilic electrode performed better in the absence of liquid water, but it was more readily flooded. A composite catalyst layer was designed with 2/3 of the area from the inlet prepared hydrophilic and the remaining 1/3 area hydrophobic. The composite catalyst layer with commercial scale dimension showed notable enhanced performance in the concentration polarization region. (C) 2004 The Electrochemical Society.

The transfer of chloride ion across an anion exchange membrane

The transfer of chloride ions into a low resistance anion exchange membrane (AEM) was investigated by cyclic voltammetry (CV) and electrochemical impedance spectra. In all cases, concentration polarization of Cl- ions is exterior to the membrane. It controls the flux and produces the limiting currents: either steady state or transient (peak type) current. In CV experiments, when the size of the holes in the membrane was much smaller than the distance between membrane holes, the Cl- anion transfer showed steady state voltammetric behavior. Each hole in the membrane can be regarded as a microelectrode and the membrane was equivalent to a microelectrode array in this condition. When the hole in the membrane was large or the distance between membrane holes was small, the CV curve of the Cl- anion transfer across the membrane showed a peak shape, which was attributed to linear diffusion. In AC impedance measurement, the impedance spectrum of the membrane system was composed of two semicircles at low DC bias, corresponding to the bulk characteristics of the membrane and the kinetic process of ion transfer, respectively. The bulk membrane resistance increases with increasing DC bias and only one semicircle was observed at higher DC bias. The parameters related to kinetic and membrane properties were discussed.

Gas exchange by bubbles in waves

A simple and feasible model feet the calculation of the gas transfer by bubble clouds is proposed in this article. N-2, O-2, and CO2 transferred by bubble clouds are obtained. At wind speed of 10 m/s, the calculated supersaturation of dissolved oxygen is 1.93-3.89% in agreement with the measurement.

Marangoni-Benard instability with the exchange of evaporation at liquid-vapour interface

A new two-sided model rather than the one-sided model in previous works is put forward. The linear instability analysis is performed on the Marangoni-Benard convection in the two-layer system with an evaporation interface. We define a new evaporation Biot number which is different from that in the one-sided model, and obtain the curves of critical Marangoni number versus wavenumber. The influence of evaporation velocity and Biot number on the system is discussed and a new phenomenon uninterpreted before is now explained from our numerical results.

Study on current-random wave forces acting on a framework

The forces of random wave plus current acting on a simplified offshore platform (jacket) model have been studied numerically and experimentally. The numerical results are in good agreement with experiments. The mean force can be approximated as a function of equivalent velocity parameter and the root-mean-square force as a function of equivalent significant wave height parameter.

Steady Current Induced Seabed Scour around a Vibrating Pipeline

Most of the existing researches either focus on vortex-induced vibrations (VIVs) of a pipeline near a rigid boundary, or on seabed scour around a fixed pipeline. In this study, the coupling effects between pipeline vibration and sand scour are investigated experimentally. Experimental results indicate that there often exist two phases in the process of sand scouring around the pipeline with an initial embedment, i.e. Phase I: scour beneath pipe without VIV, and Phase II: scour with VIV of pipe. During Phase II, the amplitude of pipe vibration gets larger and its frequency gets smaller while the sand beneath the pipe is being scoured, and finally the pipe vibration and sand scour get into an equilibrium state. This indicates that sand scouring has an influence upon not only the amplitude of pipe vibration but also its frequency. Moreover, the equilibrium scour depth decreases with increasing initial gap-to-diameter ratio for both the fixed pipes and vibrating pipes. For a given value of initial gapto- diameter ratio (e0/D), the vibrating pipe may induce a deeper scour hole than the fixed pipe in the examined range of initial gap-to-diameter ratios (−0.25 < e0/D < 0.75).

Experiments on interaction between current-induced vibration and scour of submarine pipelines on sandy bottom

In order to understand the dynamic behavior of submarine pipelines exposed to current and the mechanism of the interaction between current-induced vibration and scour of pipelines on a sandy bottom, an experimental investigation is conducted with a small scale model A test model which can be tested in the flume is set up by taking into account the typical working conditions of the pipelines and by applying the similarity theory. The interactions between the shape of the scour hole and the behavior of the pipeline as well as the flow patterns of the current are detailed, and the interaction mechanism outlined. The effect of vibration of the pipeline on the development of dynamic scour at different stages is found out. The proposed experimental method and test results provide an effective means for design of marine pipelines against scouring.