Effect of B and Fe substitution on structure of AB_3-type Co-free hydrogen storage alloy

A series of hydrogen storage Co-free AB3-type alloys were directly synthesized with vacuum mid-frequency melting method,within which Ni of La0.7Mg0.3Ni3 alloy was substituted by Fe,B and(FeB) alloy,respectively.Alloys were characterized by XRD,EDS and SEM to investigate the effects of B and Fe substitution for Ni on material structure.The content of LaMg2Ni9 phase within La0.7Mg0.3Ni3 alloy reaches 37.9% and that of La0.7Mg0.3Ni2.9(FeB)0.1 alloys reduces to 23.58%.Among all samples,ground particles with different shapes correspond to different phases.The major substitution occurs in LaMg2Ni9 phase.Electrochemical tests indicate that substituted alloys have different electrochemical performance,which is affected by phase structures of alloy.The discharge capacity of La0.7Mg0.3Ni3 alloy reaches 337.3 mA·h/g,but La0.7Mg0.3Ni2.9(FeB)0.1 alloy gets better high rate discharge(HRD) performance at the discharge rate of 500 mA/g with a high HRD value of 73.19%.

Microstructure and electrochemical properties of LaNi_(4-x)FeMn_x (x=0-0.8) hydrogen storage alloys

In order to reduce the cost of LaNi5 based hydrogen storage alloys, effect of substitution of Mn for Ni on structural and electrochemical properties of LaNi4-xFeMnx (x=0-0.8) hydrogen storage alloys was studied systematically. X-ray diffraction (XRD) and scanning electron microscope (SEM) showed that LaNi5 and La2Ni7 phases were invariably present in all alloy samples, and when x >= 0.4, (Fe, Ni) phase was observed. Electrochemical studies revealed that the discharge capacity reached a maximum value of 306.4 mAh/g when x=0.2 and the cycling stability decreased with the increase of x. With the increase of Mn content, hydrogen diffusion coefficient decreased, whereas high rate discharge-ability (HRD) and exchange current density first increased slowly when x <= 0.2 and then decreased markedly when x=0.8, indicating that electrochemical reaction on the surface of alloy electrodes had strong influence on kinetic property.

Composition optimization and electrochemical characteristics of Co-free Fe-containing AB_5-type hydrogen storage alloys through uniform design

In order to reduce the cost of ABs-type hydrogen storage alloys, effects of substitution of Ce for La （A side） and Fe, Mn, Al for Ni （B side） on structural and electrochemical properties of （LaCe）;（NiFeMnAl）s alloys were studied systematically. To make component uniform and operation easy, uniform design （UD） method was introduced into the study of composition optimization of Co-free Fe-containing ABs-type alloys for the first time. X-ray diffraction （XRD） results showed that the designed alloys were of single CaCus-type structure phase. The replacement of Fe had a severe effect on electrochemical capacity, and the substitution of Fe and A1 had a synergetic action among the unit cell volume, cycling stability and high rate discharge property. Interestingly, it was found that the hydrogen storage alloys with excessively high plateau pressure showed a tilted line in Nyquist plot instead of the semicircle, and the current decayed rapidly to near zero at the beginning of the step in constant potential step （CPS）, indicating that electrochemical impedance spectra （EIS） and CPS cannot accurately measure the electrochemical kinetics process of the hydrogen storage alloys with excessively high plateau pressure.

热处理对AB3型无Co贮氢合金电化学性能的研究

用真空熔炼法制备了多种贮氢合金原样,分别经不同温度、时间热处理和保护气氛下球磨处理。改性前后样品晶体结构用SEM和XRD测试进行结构表征,结果表明合金为LaNi5和LaMg2Ni9晶相的复合相,经过热处理的合金颗粒粒径变小针刺变少、分布也相对更均匀。采用LANDAN进行电化学相关测试(电流密度为150mA/g),表明经过热处理使得晶体结构优化,放电容量有显著增加,且经由Al替代Ni的合金容量达到353.7mAh/g,循环50周容量保持率为76.7%,循环100周容量保持率为62.7%,表现出更好的循环稳定性。实验结果表明,无Co替代贮氢合金经热处理后电化学性能有显著提高,有望降低合金材料成本的同时提高材料的环境友好性。