Detection And Mechanism Of Hydrogen Absorption And Desorption Capacity Decay Of RE-Mg-Ni Hydrogen Storage Alloy

With the rapid development of modern science and technology,especially in recent years,the research of hydrogen energy has made rapid progress.The La-Mg-Ni system hydrogen storage alloy has become one of the research hotspots with the advantages of high theoretical capacity,good activation performance and so on.Among them,the theoretical hydrogen storage capacity of AB₂ alloy is very high,but the actual capacity is relatively low,and the cycle performance is poor,and the capacity is decaying,so how to solve these problems has become the main research direction of this kind of alloy.In this paper,the phase structure,composition and morphology of the alloy were analyzed by X-ray diffraction?XRD?,scanning electron microscopy?SEM?and transmission electron microscopy?TEM?,and the gas absorption and desorption capacity and cycle performance of the alloy were studied by the severt tester,a gas storage performance test equipment.The phase composition of the alloy was analyzed by XRD.It was found that the main phases of the alloy were?LaSm?MgNi₄ phase and LaNi₅ phase.No matter the quenching speed or the number of cycles,the phase composition of the alloy did not change.After 30cycles of hydrogen absorption and desorption,the diffraction peak of the main phase of the alloy widens,forming the?LaSm?MgNi₄-H hydride amorphous phase.In addition,the LaNi₅phase is still crystalline.With the increase of quenching speed,the half peak width of diffraction peak becomes larger,which may be due to the grain refinement caused by rapid quenching and the large amount of lattice stress stored.SEM showed that with the increase of the number of cycles,the diameter and size of the alloy particles decreased obviously,and the phenomenon of pulverization appeared,and the crack width on the alloy particles widened.However,the degree of pulverization of high quench alloy is smaller than that of low quench alloy.In the TEM image,the structure of LaNi₅ phase is still crystal,but the main phase?LaSm?MgNi₄ changes after hydrogen absorption and desorption:from crystal to amorphous,which is the reason of capacity attenuation.The hydrogen absorption and desorption properties of the alloy with different quenching rates and cycles were tested.It was found that the amount of hydrogen absorption and desorption decreased with the increase of the number of cycles,and the hydrogen absorption of 5m/s alloy decreased greatly from 1.6082wt%of the first hydrogen absorption to 0.6902wt%of the 30th hydrogen absorption.The quenching rate has some influence on the stability of hydrogen absorption.After 30 cycles,the hydrogen retention rate was 41.80%?3m/s?,42.92%?5m/s?and 46.47%?10m/s?,respectively.The quenching rate can improve the cycle stability of the alloy.The software ABAQUS was used to simulate the crack stress of alloy particles.The results show that the crack width increases with the increase of stress.