Phase structure and electrochemical properties of La_(1.7+x)Mg_(1.3-x)(NiCoMn)_(9.3)(x=0-0.4) hydrogen storage alloys

The phase structure and electrochemical properties of La1.7＋xMg1.3-x（NiCoMn）9.3（x=0-0.4） alloys were investigated. The XRD analysis reveals that the alloys consist of LaNi5 phase and other phases, such as LaMg2Ni9 phase （PuNi3 structure） and La4MgNi19 phases （Ce5Co19＋Pr5Co19 structure, namely A5B19 type）. With the increase of the x value, the LaMg2Ni9 phase fades away and La4MgNi19 phases appear, while the abundance of LaNi5 phase firstly increases and then decreases. At the same time, the cell volume of LaNi5 phase and LaMg2Ni9 phase decreases. The electrochemical measurement shows that alloy electrodes could be activated in 4-5 cycles, and with the increase of the x value, the maximum discharge capacity gradually increases from 330.9 mA-h/g （x=0） to 366.8 mA-h/g （x=0.4）, but the high-rate dischargeability （HRD） and cyclic stability （S） decrease somewhat （x=0.4, HRD600=82.32%, S100=73.8%）. It is found that the HRD is mainly controlled by the electrocatalytic activity on the alloy electrode surface, and the decline of cyclic stability is due to the appearance of A5B19 type phase with larger hydrogen storage capacity, which leads to larger volume expansion and more intercrystalline stress and then easier pulverization during charging/discharging.

Effect of praseodymium substitution for lanthanum on structure and properties of La_(0.65-x)Pr_xNd_(0.12)Mg_(0.23)Ni_(3.4)Al_(0.1)(x=0.00–0.20) hydrogen storage alloys

In order to investigate the effect of substituting La with Pr on structural and hydrogen storage properties of La-Mg-Ni system （AB3.5-type） hydrogen storage alloys, a series of La0.65-xPrxNd0.12Mg0.23Ni3.4Al0.1（x=0, 0.10, 0.15, 0.2） hydrogen storage alloys were prepared. X-ray diffraction （XRD）, scanning electron microscopy （SEM） and energy dispersive spectrometer （EDS） analyses revealed that two alloys （x=0.0 and 0.10） were composed of （La,Mg）2（Ni,Al）7 phase, La（Ni,A1）5 phase and （La,Mg）Ni2 phase, while other alloys （x=0.15 and 0.20） consisted of （La,Mg）2（Ni,A1）7 phase, La（Ni,A1）5 phase, （La,Mg）Ni2 phase and （La,Mg）（Ni,A1）3 phase. All alloys showed, however, only one pressure plateau in P-C isotherms. The Pr/La ratio in alloy composition influenced hydrogen storage capacity and kinetics properties. Electrochemical studies showed that the discharge capacity decreased from 360 mAh/g （x=-0.00） to 335 mAh/g （x=-0.20） as x increased. But the high-rate dischargeability （HRD） of alloy electrodes increased from 26% （x=0.00） to 56% （x=-0.20） at a discharge current density of Id=1800 mA/g. Anode polarization measurements were done to further understand the electrochemical kinetics properties after Pr substitution.

Geometric Effects of La_(1+x)Mg_(2-x)Ni_9 (x=0.0~1.0) Ternary Alloys on Their Hydrogen Storage Capacities

Structural analysis was made using X-ray diffraction (XRD) Rietveld refinement on a series of La1+xMg2-xNi9 (x=0.0-1.0) ternary alloys. Results showed that each of La1+xMg2-xNi9 alloys was a PuNi3-type structure stacked by LaNi5 and (La, Mg) Ni2 blocks. Electrochemical tests revealed that discharge abilities of these La-Mg-Ni ternary alloys mainly depended on their atomic distances between (La, Mg) and Ni, which could be modified by varying the atomic ratios of La/Mg.

Compositional tuning of A_(2)B_(7)-type La_(0.7-x)Y_(x)Mg_(0.3)Ni_(3.5)alloys for gaseous hydrogen storage

Rare earth-based superlattice alloys have great potential for gaseous hydrogen storage,as well as successful application as nickel-metal hydride batteries anodes.In this work,Y substitution was carried out to adjust the gaseous hydrogen storage properties of A_(2)B_(7)-type La_(0.7)Mg_(0.3)Ni_(3.5)alloys.The results indicate a multiphase structure in the alloys comprised of the main rhombohedral Gd_(2)Co_(7)and PuNi_(3)phases,with a small amount of CaCu_(5)phase.Moreover,the Y substitution results in higher abundance of the Gd_(2)Co_(7)phase.The alloy La_(0.42)Y_(0.28)Mg_(0.3)Ni_(3.5)exhibits a hydrogen storage cap acity of 1.55 wt%at 298 K and a desorption plateau pressure of 0.244 MPa.In addition,this alloy demonstrates a stable cycle life by a capacity retention of 94.2%after 50 cycles,with the main capacity degradation occurring during the initial 20 cycles.This work accentuates the potential of the La-Y-Mg-Ni-based superlattice alloys for applications in solid-state hydrogen storage.

Microstructures and hydrogen storage properties of as-cast and copper-mould-cast LaMg_4Ni alloys

Phase compositions, morphologies and hydrogen storage properties of the as-cast and copper-mould-cast LaMgaNi alloys were studied. The dehydriding onset temperature of the as-cast alloy hydride was about 500 K, which was at least 50 K higher than that of the copper-mould-cast one, and the copper-mould-cast alloy hydride had a faster dehydriding rate compared with as-cast one. Additionally, the copper-mould-cast alloy could uptake 2.85 wt.% hydrogen, which was 95.0% of saturated hydrogen storage capac- ity at room temperature. While only 1.80 wt.% hydrogen （60% of saturated capacity） was absorbed for the as-cast alloy under the same conditions. The reversible hydrogen storage capacities and plateau hydrogen pressures of the two alloys were close. X-ray dif- fractions and scanning electron microscopy results indicated that similar thermodynamic property of the two alloys should be ascribed to the same hydrogen storage phase, Mg and MgzNi. The better hydrogen sorption kinetics of copper-mould-cast alloy should be as- cribed to the more uniform phase distribution compared with that of the as-cast one.

Electrochemical properties of cobalt-free La_(0.80)Mg_(0.20)Ni_(2.85)Al_(0.11)M_(0.53) (M=Ni,Si,Cr,Cu,Fe) alloys

In order to investigate the effect of different B-site additions on phase structure and electrochemical properties of cobalt-free La-Mg-Ni based alloys, La0.80Mg0.20Ni2.85Al0.11M0.53 （M=Ni, Si, Cr, Cu, Fe） hydrogen storage alloys were prepared and studied systematically. X-ray powder diffraction showed that the alloys consisted mainly of LaNi3 phase and LaNi5 phase except that Cr addition caused a minor Cr phase. Electrochemical testing indicated that alloys with additional Ni, Cr, Cu or Fe were activated within only 1-2 cycles, while that with Si addition needed 4 cycles. Adding Si, Cu and Fe increased cycling stability of La-Mg-Ni based alloys. However, maximum discharge capacity decreased from 362 mAh/g to 215 mAh/g in the order of Ni〉Fe〉Cu〉Cr〉Si. In addition, electrochemical kinetics of alloy electrodes was also researched by measuring high rate discharge ability （HRD）, hydrogen diffusion coefficient （D） and limiting current density （IL）.

LaMg_(11)Zr+Ni合金电极电化学性能研究

以LaMg11Zr为母体合金,由机械合金化方法制备LaMg11Zr+200%N i合金,用X射线衍射(XRD)测定球磨时间对非晶相化的影响,20 h合金即可达到完全非晶态化,合金电极化学性能和循环寿命最好.

回归分析在Mg_2Ni系合金储氢性能研究中的应用

以Al、Ti含量和制备方法为试验因素,采用回归分析方法,建立出具有较高预测精度的Mg2Ni系储氢合金最大吸氢量和最大放电容量的回归方程,并进行了Mg2Ni系合金储氢性能的优化研究。结果表明,具有最佳储氢性能的Mg2Ni系储氢合金的试验参数为Al含量0.1%、Ti含量0.1%;制备方法为两步法,制备出的Mg1.8Al0.1Ti0.1Ni合金的最大吸氢量高达3.47%,最大放电容量高达102.5 mA·h/g,且经15次循环后的放电容量仍保持在69.1 mA·h/g。

复相La-Mg-Ni系贮氢合金的退火研究进展

退火处理对复相La-Mg-Ni系贮氢合金的组织和电化学行为影响较大,介绍了近年来La-Mg-Ni系贮氢合金退火后,合金中Mg含量、微观结构、压力-组成-温度(PCT)特性曲线以及电化学行为的研究状况。分析了复相La-Mg-Ni系贮氢合金的发展应用仍需解决的问题,旨在为提高贮氢合金的电化学性能提供思路和依据。