Effect of cobalt substitution for nickel on microstructural evolution and hydrogen storage properties of La 0.66 Mg 0.34 Ni 3.5- x Co x alloys

Superlattice hydrogen storage alloys offer a compelling advantage with rapid hydriding rate and high storage capacity. However, its practical applications face challenges including complex structure, low dehydriding capacity, and cyclic instability. In this work, we successfully prepared La 0.66 Mg 0.34 Ni 3.5- x Co x superlattice hydrogen storage alloys with enhanced dehydriding capacity and stability by partially substituting Co for Ni. X-ray diffraction (XRD) re finements analysis reveals the presence of (La,Mg) 3 Ni 9 , (La,Mg) 5 Ni 19 , and LaNi 5 phases within the alloy. Following Co substitution in the La 0.66 Mg 0.34 Ni 3.4 Co 0.1 alloy, there is a signi ficant increase in content of the (La, Mg) 3 Ni 9 phase and a reduction in the hysteresis factor, resulting in an improved reversible hydrogen storage capacity from 1.45 wt% to 1.60 wt%. The dehydriding kinetics of the alloy is controlled by diffusion model with an activation energy of 8.40 kJ/ mol. Furthermore, the dehydriding enthalpy value of the Co -substituted alloy decreases from 30.84 to 29.85 kJ/mol. Impressively, the cycling performance of the alloy after Co substitution exhibits excellent stability, with a capacity retention rate of 92.3% after 100 cycles. These findings provide valuable insights for the development of cost-effective hydrogen storage materials. (c) 2024 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.