Effect of Y content on the microstructure and hydrogen storage properties of annealed La1-Y MgNi3.8Al0.2 (x = 0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys

Current La-Mg-Ni-based hydrogen storage alloys suffer from rapid capacity decay, which limits their practical applications. The cast LaMgNi4 alloy requires about 20 min of saturation hydrogen absorption at 373 K, 3 MPa, with a capacity retention of 44.2 % after 20 cycles. In this paper, the B-side element Ni is partially replaced by the larger atomic radius Al element, which can reduce the difference in nuclear radius between the two sides of the alloy and reduce the lattice distortion effect in the process of hydrogen absorption and desorption, and the addition of rare-earth element Y can preferentially replace the rare-earth element La in the [A2B4] sub-structure, which can inhibit the amorphousness of the alloy caused by the process of hydrogen absorption and desorption, and improve the conformational stability of the alloy. The as-cast hydrogen storage alloy La1-xYxMgNi3.8Al0.2 (x = 0, 0.1, 0.2, 0.3, 0.4) was annealed to improve its cycle stability. Physical phase characterization by X-ray diffractometer showed that the main phases of the hydrogen storage alloy were the LaMgNi4 phase and LaNi4.5Al0.5 phase. The elemental distribution of the annealed hydrogen storage alloys was more uniform when scanning electron microscopy was performed. All the annealed hydrogen storage alloys were fully activated after a hydrogen absorption/desorption cycle. The annealed hydrogen storage alloy La0.7Y0.3MgNi3.8Al0.2 showed excellent hydrogen absorption/desorption kinetics. It possessed good cycling performance, with an activated hydrogen absorption capacity of 1.614 wt% and a 50th hydrogen absorption capacity of 1.178 wt% at a temperature of 333 K and 3 MPa hydrogen pressure. The capacity retention rate was 70.8 % after 50 hydrogen absorption/desorption cycles. It is shown that the elemental substitution method and heat treatment are beneficial in improving the cycle stability of La-Mg-Ni-based hydrogen storage alloys. This study contributes to the development of La-Mg-Ni-based hydrogen storage alloys.