采用Ce﹑Pr和Nd少量混合稀土部分替代La,采用感应熔炼及高温退火工艺制备(La_(0.7)Ce_(0.1)Pr_xNd_(0.2-x))_(0.67)Mg_(0.33)Ni_(3.0) (x=0, 0.1, 0.2)系列贮氢合金.结果表明,与La_(0.67)Mg_(0.33)Ni_(3.0)合金相比较,混合稀土元素加入后对合金的相组成没有本质影响,(La_(0.7)Ce_(0.1)Pr_xNd_(0.2-x))_(0.67)Mg_(0.33)Ni_(3.0) (x=0, 0.1, 0.2)合金微观组织由主相PuNi_3型结构与LaMgNi_4第二相组成;随混合稀土加入和Pr含量x的增加,PuNi_3型相晶体结构的晶胞体积和a轴减小,但c轴及轴比c/a增大.电化学性能测试结果表明,用混合稀土Ce﹑Pr和Nd少量替代La后均能明显改善合金的综合电化学性能,合金的电化学容量与La_(0.67)Mg_(0.33)Ni_(3.0)合金(392.0 mAh/g)比较虽略有下降,但随Pr含量x的增加,混合稀土合金电极容量有所提高(384 mAh/g);经100次循环后,混合稀土合金电极容量保持率从La_(0.67)Mg_(0.33)Ni_(3.0)合金时的64%提高到82%~83%,其高倍率放电性能则从78.4%提高到了89%~91%.
Through substitution of mixed rare earth elements Ce, Pr and Nd for La, (La_(0.7)Ce_(0.1)Pr_xNd_(2-x))_(0.67)Mg_(0.33)Ni_)3.0) (x=0, 0.1, 0.2) hydrogen storage alloys were prepared by induction melting followed by annealing treatment. Influences of partial substitution of rare earth elements Ce, Nd and Pr for La on phase structure and electrochemical properties of (La_(0.7)Ce_(0.1)Pr_xNd_(2-x))_(0.67)Mg_(0.33)Ni_(3.0) (x=0, 0.1, 0.2 ) were investigated by means of X-ray diffraction (XRD), electron probe X-ray microanalysis (EPMA) and electrochemical measurements. XRD and back scattered electron images analysis shows that all of the alloys were composed of main phase with PuNi_3-type structure and small amount of second phase of LaMgNi_4. With the addition of the mixed rare earth elements and increasing of Pr content x, the lattice parameters c and c/a of the PuNi_3-type structure increase while cell volume and a decrease. Compared with La_(0.67)Mg_(0.33)Ni_(3.0), the electrochemical properties of the (La_(0.7)Ce_(0.1)Pr_xNd_(0.2-x))_(0.67)Mg_(0.33)Ni_(3.0) alloys were improved obviously. Although the electrochemical capacities of the alloys decreased little compared with that of La_(0.67)Mg_(0.33)Ni_(3.0) (392.0 mAh/g), the electrode capacities became increasing (384 mAh/g) when Pr content x increased. After 100 cycles, the capacity retention rates of the electrodes increased from 64% to 82.6%-83% and the high-rate dischargeabilities (HRDs) of the alloys increased from 78.4% to 89.4%-91.1%.
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