Effect of cobalt substitution for nickel on microstructural evolution and hydrogen storage properties of La0.66Mg0.34Ni3.5–xCox alloys

Abstract

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 La0.66Mg0.34Ni3.5–xCox superlattice hydrogen storage alloys with enhanced dehydriding capacity and stability by partially substituting Co for Ni. X-ray diffraction (XRD) refinements analysis reveals the presence of (La,Mg)3Ni9, (La,Mg)5Ni19, and LaNi5 phases within the alloy. Following Co substitution in the La0.66Mg0.34Ni3.4Co0.1 alloy, there is a significant increase in content of the (La, Mg)3Ni9 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.