Study on the evolution of phase and properties for ternary La-Y-Ni-based hydrogen storage alloys with different stoichiometric ratios

In recent years, some progress has been made in the development and application of the highly anticipated La-Y-Ni hydrogen storage alloy system. However, the relationship between the structure and properties of materials has not been studied systematically and thoroughly. In this paper, the evolution law of AB3-, A2B7- and A5B19-type phases for La-Y-Ni-based hydrogen storage alloys was proposed. The single-phase LaY2Ni9 (AB3), La2Y4Ni21 (A2B7) and La5Y10Ni57 (A5B19) alloys were synthesized by powder sintering method at 1173, 1353 and 1423 K, respectively. The XRD and SEM results of the alloys show that LaY2Ni9 alloy has a single PuNi3 phase (3 R), La2Y4Ni21 alloy is composed of Ce2Ni7 phase (2 H) and Gd2CO7 phase (3 R), and La5Y10Ni57 alloy contains Pr5Co19 phase (2 H) and Ce5Co19 phase (3 R). Among the three alloys, the La2Y4Ni21 alloy has the largest hydrogen storage capacity (1.59 wt%) in solid /H2 reaction at 313 K. The target alloys all exhibit excellent electrochemical activation ability. The maximum discharge capacity of LaY2Ni9, La2Y4Ni21 and La5Y10Ni57 alloys decreases gradually, but their cycle stability increases in turn. The high-rate discharge performance of La2Y4Ni21 alloy is the best, because its exchange current density (I0 = 75.55 mA/g) and hydrogen diffusion coefficient (D0 = 2.51 ×10−10 cm2/s) cooperate well. It is hoped that these findings can offer theoretical guidance and technical assistance for the development of La-Y-Ni-based hydrogen storage alloys.