Zr-based AB2 Alloys Research Articles

Hydrogen absorption behavior of Zr-based getter materials with Pd[sbnd]Ag coating against gaseous impurities

In this work, PdAg coating has been deposited on different Zr-based Lave phase alloys, including ZrV2, Zr0.9Ti0.1V2 and Zr57V36Fe7, by the electroless plating technique. It is attempted to illustrate the role of PdAg coating on hydrogenation performance of Zr-based alloys against gaseous impurities. X-ray diffraction and scanning electron microscope (SEM) observations along with energy disperse spectroscopy (EDS) give evidences that the PdAg coating has been uniformly deposited on the surface of experimental alloys. Activation behavior and hydrogenation kinetics in pure H2 and mixture gases (H2 containing 1 vol.% air) are evaluated by using a Sieverts-type apparatus. The PdAg coating accelerates the hydrogenation kinetics and slightly decreases the hydrogen storage capacity of experimental Zr-based AB2 alloys. The poisoning effect of air gaseous impurities mainly deteriorates the hydrogen absorption capacity of experimental Zr-based alloys with PdAg coating at room temperature. The PdAg coated Zr0.9Ti0.1V2 preserves the fastest hydriding reaction rate at 303 K and 673 K among three experimental alloys. The slope value in the rapid absorbing stage (ka1) in mixture gases at each temperature of PdAg coated Zr-based AB2 alloys is quite higher than that of the corresponding bare alloy which indicates the uniform PdAg coating evidently improves the poison resistance capability of alloys in a wide temperature range. The PdAg coating does not fall off significantly from the surface after 6 times hydrogenation/dehydrogenation cycles.

Diffusion of hydrogen interstitials in Zr basedAB2 and mischmetalbased AB5 alloys

The Zr based AB2 alloys ZrMnFe0.5Ni0.5,ZrMnFe0.5Co0.5 and mischmetal(Mm) based AB5 alloy MmNi3.5Al0.5Fe0.5Co0.5 have been prepared and characterized by means of powder x-ray diffractograms. The hydrogenabsorption kinetics of these alloys have been studied in the temperature and pressure ranges450–650 °C and 10–100 mbar respectively with a maximum H to host alloy formula unit ratio of 0.01,using a pressure reduction technique. The diffusion coefficient of the hydrogen interstitialshas been determined from hydrogen absorption kinetics experiments. The dependence ofthe diffusion coefficient on the alloy content has been discussed. For Mm basedMmNi3.5Al0.5Fe0.5Co0.5 alloy, the diffusion coefficient is about an order of magnitude higher than that of the Zrbased alloys.

Advanced nanocrystalline Zr-based AB2 hydrogen storage electrode materials for NiMH EV batteries

Abstract The metallurgical microstructure, crystal-structure and electrochemical properties of Laves phase Zr–V–Mn–Ni system alloys (modified with Ti, Co, Sn, etc.) were investigated systematically in the present paper. Conventional polycrystalline Zr-based alloys, which consist of cubic C15 Laves phase, hexagonal C14 Laves phase and non-Laves phase (such as Zr7Ni10, Zr9Ni11, Zr(NiMn)Sn0.35), show the highest discharge capacity of 342 mAh g−1 (at 60 mA g−1 charge–discharge current), which decreases by 7.8% after 300 cycles. Amorphous phase alloys in melt-spun alloys exhibit poor electrochemical properties. Advanced nanocrystalline C15-Laves single-phase alloys were prepared by completely crystallizing the melt-spun amorphous Zr1−xTix[(NiVMnCo)1−ySny]2+α alloys. These alloys have a special microstructure composed of high-density interface phase and random-oriented grains varying from several nanometres to several dozens of nanometres. It was found that these materials had high discharge capacity (the maximum capacity is up to 379 mAh g−1) and long cycle life (the capacity only decreases 3% after 300 cycles). The maximum discharge capacities were found in the metallurgical microstructure and crystal-structure in Zr-based AB2 alloys. The maximum discharge capacity increases in regular nanocrystalline/C15-Laves single-phase>polycrystalline/multi-phase (Laves and non-Laves)>comorphous state/C15-Laves single-phase. It was shown that the complete crystallization method from amorphous solids is an effective way to greatly improve the electrochemical performance of Zr-based AB2 hydrogen storage electrode materials, which is not only significant for academic research but also valuable for practical applications in the NiMH battery system for pure electric vehicles (PEV) and hybrid electric vehicles (HEV).

Improvement of the electrochemical properties of Zr-based AB2 alloys by an advanced fluorination technique

Abstract An advanced fluorination technique has been developed for improving the electrochemical performances of Zr-based AB2 alloys. During the procedure, alloys were ball milled in a complex fluoride solution. It was found that the electrode of the treated alloy exhibited excellent electrochemical performance. Its activation property and high-rate discharge capability were found to be satisfactory compared with the conventional AB5-based electrodes. The electrode demonstrated a significant decrease of the reaction resistance measured by an impedance spectrometric method. The F-treated alloy was found to give a larger specific surface area and to form a highly Ni-covered surface.

Corrosion and degradation behavior of Zr-based AB2 alloy electrodes during electrochemical cycling

Zr-based AB 2 Laves phase alloys are promising materials for the negative electrodes in Ni–MH batteries. In this work, their cyclic durability and corrosion behavior in the electrolyte were systematically investigated using instrumental analyses such as ICPS, XRD, SEM, EPMA, XPS as well as PCT and specific surface area measurement.

High Performance Zr-based Metal Hydride Alloys For Nickel Metal Hydride Batteries

ABSTRACTBased upon Ovonic's multi-element, atomic engineering approach, two families of alloys are being used in commercial Nickel Metal Hydride (NiMH) rechargeable batteries, i.e. the mischmetal (Mm) based AB5 and Zr based AB2 alloys. While Mm based alloys are faster to activate, are limited by a discharge capacity of only 320–340 mAh/g. The Zr based alloy, although slightly slower to activate, provides a much higher discharge capacity. In this paper, we first discuss the use of Ovonic's multi-element approach to generate a spectrum of disordered local environments. We then present experimental data to illustrate that through these atomically engineered local environments, we are able to control the hydrogen site occupancy, discharge capacity, kinetics, and surface states. The Zr based alloy with a specific discharge capacity of 465 mAh/g and excellent rate capability has been demonstrated.

Hydriding characteristics in (Ti,Zr)(Ni,Mn,X)2 alloys

AB2 type Laves alloy has a high absorption capacity for hydrogen per unit weight. The plateau flatness and the hysteresis of pressure-composition-temperature (PCT) curves are important factors for high-performance hydrogen storage applications. Systematic research was performed on Zr-based AB2 alloy from the viewpoint of the element. The relationship between the PCT properties and the many fundamental parameters is discussed. The plateau pressure could be controlled by the weight ratio of A site and B site elements. We found a high-performance hydrogen storage alloy for storage applications in the (Ti,Zr)(Ni,Mn,X)2 alloy system.

電子・機能材料 （Ｔｉ，Ｚｒ）（Ｎｉ，Ｍｎ，Ｘ）２合金の水素吸蔵特性

AB2 type Laves alloy has the high absorption capacity of hydrogen per unit weight. The plateau flatness and the hysteresis of pressure-composition-temperature (PCT) curves are important factors for high-performance hydrogen storage applications.Systematic research was performed about Zr-based AB2 alloy. The relationship between the PCT properties and the several fundamental parameters are discussed. The plateau pressure could be controlled by the weight ratio of A site and B site elements. We found hydrogen storage alloy for the storage applications which has a high performance in (Ti, Zr) (Ni, Mn, X)2 alloy system.