Hydrogen storage properties of La_1−xPr_xMgNi_3.6Co_0.4 (x = 0–0.4) alloys with annealing treatment

The as-cast RE–Mg–Ni-based AB₂-type La_1−xPr_xMgNi_3.6Co_0.4 (x = 0–0.4) alloys were prepared by vacuum induction melting followed by annealing treatment. The phase composition and structure were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results show that LaMgNi₄ and LaNi₅ coexist in as-cast alloys, but only LaMgNi₄ is detected in the annealed alloys. The morphology of annealed alloys is more homogeneous than that of as-cast alloys. The gaseous hydrogen storage and electrochemical properties were investigated by pressure–composition isotherm (P-C-T) and electrochemical measurements. The P-C-T curves of annealed alloys show flatter and wider pressure plateaus corresponding to absorption/desorption pressure plateaus of LaMgNi₄ hydride. But the maximum hydrogen storage content of annealed alloys is lower than that of as-cast alloys. In consideration of the electrochemical properties, the annealed La_0.8Pr_0.2MgNi_3.6Co_0.4 alloy exhibits a maximum discharge capacity of 354.2 mAh·g⁻¹.