Phase forming law and electrochemical properties of A2B7-type La–Y–Ni-based hydrogen storage alloys with different La/Y ratios

The effects of different proportions of La and Y elements in the A-side on the structure and properties of A2B7-type La–Y–Ni hydrogen storage alloys were investigated. The (La,Y)2Ni7 hydrogen storage alloys with different La/Y ratios were prepared by sintering the Y2Ni4 precursor and different AB5-type precursors at 1298 K for 5 h and subsequently annealed for 20 h at 1248 K. All the alloys only contain Ce2Ni7 (2H-type) and Gd2Co7 (3R-type) phases with different mass ratios. As the La/Y ratio decreases, the cell volume of the two phases declines and the corresponding plateau pressure gradually increases. As the proportion of Y in the alloy increases, the hydrogen storage capacity increases gradually from 1.309 wt% (La/Y = 1/1) to 1.713 wt% (La/Y = 1/5) and the high-rate discharge (HRD1500) ability of the alloy electrodes increases gradually from 62.7% (La/Y = 1/1) to 88.6% (La/Y = 1/5). The hydrogen diffusion rate in the bulk of the alloy is the controlling step of hydriding/dehydriding kinetics. The Y element can effectively inhibit the hydrogen-induced amorphous (HIA) of La–Y–Ni alloys, but the poor stability of the Y element in alkaline KOH aqueous solution leads to a decrease in the electrochemical cyclic stability with increasing Y content.