Superior hydrogen storage performance of LaNi5-LaMgNi4 bi-phase La‒Mg‒Ni-based alloys

AB5-AB2 bi-phase hydrogen storage alloys not only possess the two phases of AB5 and AB2 which have complementary hydrogen storge characteristics, but also overcomes the restriction between [AB5] and [AB2] subunits of a superlattice structure, and thus considered promising for hydrogen absorption and desorption. Therefore, we designed and prepared AB5-AB2 bi-phase La‒Mg‒Ni-based La0.48Sm0.18Mg0.34Ni2.75Al0.14 and La0.26Nd0.22Sm0.18Mg0.34Ni2.77Al0.13 alloys by proper utilization of preferential atomic occupation and heat treatment. The alloys exhibit outstanding hydrogen storage properties. In particular, the Nd0.22–1123 K alloy shows an excellent gaseous cycling retention of 97.2 % after 50 cycles benefitting from the independent behaviors of AB5 and AB2, which enables very low microstrains and a very stable crystal structure against hydrogen absorption/desorption. More impressively, the Nd0.22–1123 K alloy electrode exhibits a superior high-rate discharge performance of 83.2 % at 1500 mA g−1 due to the synchronized hydrogen absorption and desorption during charge/discharge, which accelerates the diffusion of hydrogen atoms and realizes a high electrochemical kinetics. The present study puts forward a reasonable solution to effectively improve the cycle life and electrochemical hydrogen desorption of La‒Mg‒Ni-based alloys for both gaseous and electrochemical hydrogen storage.