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采用感应熔炼技术在Ar气氛保护下制备得到LaMg2Ni与Mg2Ni合金。X射线衍射(XRD)图表明LaMg2Ni合金在吸氢过程中分解为LaH3相和Mg2NiH4相,放氢过程中LaH3相转化为La3H7相。与Mg2Ni合金相比,LaMg2Ni合金显示出优良的吸氢动力学性能,这是由于镧氢化合物的存在及其在吸氢过程中所发生的相转变所造成的。LaMg2Ni合金280 s内吸氢即可达到最大储氢量的90%以上,而Mg2Ni合金则需要1200 s才能达到,且在相同温度下LaMg2Ni合金的吸氢反应速率常数大于Mg2Ni合金速率常数。镧氢化合物不仅有利于改善动力学性能,而且可以提高热力学性能。LaMg2Ni合金中的Mg2Ni相氢化反应焓与熵分别为-53.02 kJ.mol-1和84.96 J.K-1.mol-1(H2),这一数值小于单相Mg2Ni氢化反应焓与熵(-64.50 kJ.mol-1,-123.10 J.K-1.mol-1(H2))。压力-组成-温度(P-C-T)测试结果表明在603 K至523 K温度范围内,LaMg2Ni合金储氢容量保持稳定为1.95wt%左右,然而Mg2Ni合金的储氢容量则由4.09wt%衰减为3.13wt%,Mg2Ni合金的储氢容量在523K低温下仅为603 K时的76.5%,表明镧氢化合物能够改善Mg2Ni合金低温下的吸放氢性能。
LaMg2Ni and Mg2Ni alloys were prepared by induction melting under Ar atmosphere. X-ray diffraction (XRD) patterns show that the LaMg2Ni alloy decomposes into the phases LaH3 and Mg2NiH4 during hydrogen absorption and the phase of LaH3 to La3H7 during the hydrogen desorption. Compared with Mg2Ni alloy, LaMg2Ni alloy shows excellent hydrogen absorption kinetics, which is due to the presence of lanthanum hydrogen compounds and their phase transitions during hydrogen absorption. LaMg2Ni alloy can absorb more than 90% of its maximum hydrogen content within 280 s, while Mg2Ni alloy takes 1200 s to achieve, and the hydrogen absorption rate constant of LaMg2Ni alloy is higher than that of Mg2Ni alloy at the same temperature. Lanthanum hydrogen compounds not only help to improve the kinetic properties, but also can improve the thermodynamic properties. The enthalpy and entropy of the hydrogenation reaction of Mg2Ni phase in LaMg2Ni alloy are -53.02 kJ.mol-1 and 84.96 JK-1.mol-1 (H2), respectively, which is lower than that of single-phase Mg2Ni hydrogenation reaction (-64.50 kJ). mol-1, -123.10 JK-1 mol-1 (H2)). The pressure-composition-temperature (PCT) test results showed that the hydrogen storage capacity of LaMg2Ni alloy remained stable at 1.95wt% in the temperature range of 603 K to 523 K, while the hydrogen storage capacity of Mg2Ni alloy decreased from 4.09wt% to 3.13wt% %. The hydrogen storage capacity of Mg2Ni alloy is 76.5% at 603K at 523K, which indicates that lanthanum hydrogen compounds can improve the hydrogen storage and desorption performance of Mg2Ni alloy at low temperature.