Lei Yongquan

The electrochemical charge-discharge properties of ZrCrNi hydrogen storage alloys

Abstract Zr(Cr x Ni 1− x ) 2 (0.15 ⩽ x ⩽ 0.65) alloys were prepared by arc melting in an argon atmosphere. Through X-ray diffraction, the main crystal structure of the alloys was found to change from Laves phase cubic C15 to hexagonal C14 as the Cr to Ni ratio increased, and lattice parameters and hydrogen absorption capacities were mainly determined by the Cr content. The alloy Zr(Cr 0.35 Ni 0.65 ) 2 , which was mainly of C15 Laves phase structure, was found to have maximum electrochemical discharge capacity of 305 mA h g −1 at 298 K. The activation behaviors of Zr Cr Ni-based hydride electrodes were also studied. Fine alloy powders, especially those pulverized by cycling in hydrogen gas and where the electrodes were pre-treated with HF-H 2 O 2 solution, were highly activated. As both Zr and Cr have a high resistance against alkaline solution, it is reasonable for Zr Cr Ni alloy electrodes to have durable cycle lives. The chemical valence states and composition of electrode surfaces were also analyzed with X-ray photoelectron spectroscopy before and after charge-discharge cycling. An obvious variation in the Zr 3d 5/2 peak position before and after cycling was detected. The discrepancy is ascribed to the chemical environment differences of Zr atom in primordial and activated surface layers.

Activation mechanism of hydrogen-storage electrode alloy Ml(NiCoMnTi)5 produced by gas atomization

Abstract Electrochemical activation behaviour of hydrogen-storage alloy Ml(NiCoMnTi) 5 produced by conventional induction melting (CIM) and by Ar gas atomization (AGA) has been studied. It has been found that the surface oxide layer plays a minor part, while the change of energy inside alloy before and after hydriding is the major factor affecting the behaviour of activation. The larger the change of energy inside the alloy or the strain energy caused by H-atoms entering tetrahedral and octahedral sites during hydriding, the more difficult is the activation. The effect of surface oxide film on the activation could to be considered as the oxide film causing the energy of Hatoms entering the alloy to be increased, since H-atoms must consume some energy to break the surface oxide film initially, before entering the alloy.

The effects of etching with HCl on the hydrogen sorption properties of Mg2Ni

Abstract The effects of etching with HCl on the hydrogen sorption properties of Mg 2 Ni have been investigated. On being etched with HCl, Mg 2 Ni can be activated and hydrided easily at room temperature and its low temperature desorption kinetics are improved. However, its hydriding is incomplete at room temperature and its room temperature hydrogen absorption capacity degrades rapidly on cycling. X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy analyses show that the etching treatment removes the magnesium oxide overlayer and preferentially dissolves away magnesium; this results in a new surface layer composed mainly of porous, metallic nickel microspheres. We believe that the nickel microspheres act as the active catalyst for hydrogen absorption and desorption at lower temperatures. The incomplete hydriding and the cycling degradation of the hydrogen absorption capacity at room temperature are caused, we suggest, by the cracking and disintegration of the alloy powder on each cycle, with the newly generated surfaces deactivating very quickly.

Influence of Temperature on Electrochemical Performances of Rare Earth Based Hydrogen Storage Material

In view of the higher temperature of largesize Ni/MH battery in electric vehicle, the effect of temperature on electrochemical performances of hydrogen storage alloy Ml(NiCoMnTi)5 was investigated systematically. The results show that the electrochemical performances of alloy vary drastically with temperature changing. As temperature rises, the hydrogen equilibrium pressure increases, the width of hydrogen desorption plateau decreases and the gradient increases, leading to a decline of capacity. When temperature rises from 20 °C to 80 °C, the discharge capacity of the alloy decreases from 309.11 mA· h· g−1 to 227.64 mA · h · g−1, but the high rate dischargeability is improved markedly. Higher temperatures also bring about a significant decrease in the cycling stability and selfdischarge property. X-ray diffraction analysis indicates that the alloy has a single phase with CaCu5-type LaNi5 structure.

Influence of doped elements on electrochemical high temperature performance of La-riched hydrogen storage material

The effects of small amounts of added elements such as aluminum, titanium and zirconium to MlNi3.8(CoMn)1.2 on its electrochemical performances and performances at high temperatures were investigated. It is found that the addition of aluminum brings about a significant, increase in the discharge capacity at high temperatures, and the capacity decay, during repeated charge-discharge cycles and the self-discharge are both suppressed, while the rate capability decreases. The alloy containing zirconium exhibits a longer cycle life and a better rate capability, but a much lower discharge capacity. The addition of titanium improves the rate capability, but the capacity decreases greatly. An X-ray diffraction analysis indicates that a second phase exists in the alloy with additive Zr or Ti, which improves the discharge-rate characteristics, and the superior stability of the alloy with additive Al may be due to the expansion of lattice parameters and cell volume.