Hydrogen storage behavior and capacity degradation mechanism of single-phase A5B19-type La-Y-Ni-based alloy

La–Y–Ni-based alloys show great promise for near-room-temperature solid-state hydrogen storage, but the effects of phase purification on performance and the underlying capacity degradation mechanisms remain unclear. Herein, La 1.9 Y 3.1 Ni 19 alloys were prepared via vacuum induction melting and rapid solidification, followed by annealing to regulate phase composition. Annealing at 1050 °C for 24 h successfully yielded a single-phase 3R-A 5 B 19 superlattice alloy, which exhibits optimized hydrogen storage properties. It delivers a high reversible hydrogen capacity of 1.58 wt% under 8 MPa H 2 with a rapid absorption equilibrium time of 200 s. Chou and JMA kinetic analyses indicate that the single-phase structure exhibits a more favorable apparent hydrogen absorption response under the same testing conditions. The alloy retains 85% of its initial capacity after 100 hydrogen absorption/desorption cycles. Capacity degradation is likely mainly attributed to cycling-induced amorphization. The large volume difference (3.25Å 3 ) between [AB 5 ] and [A 2 B 4 ] subunits generate severe lattice strain, which destroys the superlattice structure and degrades overall storage performance.