Effect of Y, Al Co-Doping on Hydrogen Storage Properties of La–Mg–Ni-Based Alloys

Abstract

La–Mg–Ni-based hydrogen storage alloys have excellent hydrogen storage properties. This work reports the hydrogen storage performance of a series of A₂B₇-type La_0.96Mg_0.04Ni_3.34Al_0.13 alloy and La_0.96-xY_xMg_0.04Ni_3.47–0.6xAl_0.6x (x = 0, 0.22, 0.33, 0.44) alloys, and explores the effect of Y and Al element combined substitution on the microstructure and hydrogen storage performance of A₂B₇-type La–Mg–Ni-based alloys. The alloys are composed of Ce₂Ni₇ phase and LaNi₅ phase. With the increase of x, the cell volume of Ce₂Ni₇ phase decreases, while that of LaNi₅ phase increases, indicating that Y atom mainly enters Ce₂Ni₇ phase and Al atom mainly enters LaNi₅ phase. An appropriate amount of co-substitution increases the hydrogen storage capacity and reduces the hydrogen absorption/desorption plateau pressure hysteresis of the alloy. When x = 0.44, the hydrogen storage capacity of the alloy is 1.449 wt%, and the hysteresis coefficient is 0.302. The cell volume of Ce₂Ni₇ phase and LaNi₅ phase expands to different degrees after 20 absorption/desorption cycles. With the increase of x, the volume expansion rate decreases, and the cycle capacity retention rate also gradually decreases. This is related to the amorphization of Ce₂Ni₇ phase. When x = 0.22, the capacity retention rate of the alloy is 91.4%.