Optimizing microstructure and enhancing hydrogen storage properties in Mg alloy via tailoring Ni and Si element

The inherent thermodynamic and kinetic challenges of Mg/MgH₂ hydrogen storage materials pose significant obstacles to their development. Alloying has emerged as a highly promising strategy to overcome these challenges. In this study, we synthesized a series of Mg₉₃Ni_7-x-Si_x (x = 0.4, 1.6, 5) ternary alloys through microstructure optimization and particle refinement using melting and high energy ball milling techniques. We systematically investigated the effects of varying Ni and Si content on the microstructure and hydrogen storage properties of Mg-Ni-Si alloys. The results demonstrate that variations in Ni and Si content leads to the formation of different types of intermetallic compounds within the alloys, thereby influencing their hydrogen storage properties. Among the tested alloys, Mg₉₃Ni₂Si₅ exhibits superior activation and hydrogen absorption properties. The enhanced hydrogenation performance can be attributed to the precipitation of the Mg₂Si phase resulting from increased Si content, as well as the refinement of the Mg₂Ni₃Si phase and the increase in eutectic structure Mg+Mg₁₁Ni₁₂Si₁₀. Significantly, the increased intermetallic compounds provide a large number of sites and channels for the nucleation of hydrides as well as the diffusion of hydrogen. During the dehydrogenation process, Ni, serves as the predominant catalytic species, effectively promotes the dissociation of hydrogen and enhances the reaction kinetics. As a result, the hydrogen desorption of the hydrogenated Mg₉₃Ni_6.6Si_0.4 alloy initiates at 180 °C, with a reduced activation energy of 105.21 kJ/mol. These findings underscore the synergistic and effective roles of Ni and Si elements in enhancing the hydrogen storage properties of Mg-based materials, thus supporting the development of economically viable and promising Mg-based solid-state hydrogen storage materials.