Structural and Catalytic Effect of Partial Substitution of Nickel by Niobium on the Hydrogen Storage Behaviour of Mechanically Alloyed Mg–Mg ₂ Ni Composites

Magnesium hydrides (MgH ₂ ) have been extensively studied for solid‐state storage applications. However, the industrial scalability of MgH ₂ is limited due to its high absorption/ desorption temperatures and poor kinetics. In this work, a Nb‐substituted Mg ₂ Ni catalyst (Mg ₂ Ni _0.8 Nb _0.2 ) was synthesized by the melt spinning technique. The Mg‐20 wt% of Mg ₂ Ni _0.8 Nb _0.2 composites were prepared using the high‐energy ball milling technique. The composite desorbed around 5 wt% H ₂ within 10 min at 300 °C, while retaining 97.88% of its initial absorption capacity after 20 cycles. Furthermore, the composites were hydrogenated for different times, 10, 20, and 30 min, to study the effect of hydrogenation time on the dehydrogenation behaviour of MgH ₂ . Compared with pure MgH ₂ , which exhibits an activation energy of 275.52 kJ/mol, the Mg–Mg ₂ Ni _0.8 Nb _0.2 composites showed significantly reduced activation energies of 126.35, 131.66, and 100.78 kJ/mol after hydrogenation for 10, 20, and 30 min, respectively. The improved performance is attributed to partial Nb substitution, which enhances hydrogen dissociation and reduces the activation energy for breaking Mg–H bonds.