Effect of Equivalent La and Ce Substitution for Y on the Structure and Properties of A2B7-Type La-Y-Ni-Based Hydrogen Storage Alloys

A2B7-type (LaCe) x Y6-2x Ni18.5Mn1.5Al (x = 0.95, 1.00, 1.15, 1.20, 1.25, 1.30) alloys were prepared by a vacuum induction-quenching process and annealed at 1148 K for 16 h. The structure and properties of the alloys were tested by X-ray diffraction (XRD), scanning electron microscopy (SEM), pressure-composition-temperature curve (PCT), and electrochemical methods. It is found that the alloys are mainly composed of the Ce2Ni7 (2H) and Gd2Co7 (3R) phase, and a decrease of the Y content is beneficial to the formation of the Ce2Ni7 phase. With the partial substitution of Y by equivalent La and Ce, the alloy electrodes with a moderate Y/(LaCe) ratio have relatively large discharge capacity, while the capacity retention rate increases gradually from 63.2% (x = 0.95) to 69.2% (x = 1.30) after 100 cycles. The alloy with the highest Y content shows the best electrochemical kinetic performance due to good hydrogen diffusion ability and surface reactivity. This work provides new ideas and theoretical guidance for the composition optimization of La-Y-Ni-based hydrogen storage alloys.