Liquid-phase synthesis of Mg-Nb nanocomposites with highly stable hydrogenation/dehydrogenation cycling for hydrogen storage

Magnesium hydride (MgH 2 ) is regarded as one of the most promising solid-state hydrogen storage materials. However, its practical application remains limited by thermodynamic stability, slow kinetics, and the gradual coarsening of particles during cycling. To address these limitations, we synthesized a stoichiometrically adjustable Mg-Nb nanocomposite using a liquid-phase in-situ growth strategy. Optimization revealed that the Mg-Nb (10:1) composite exhibits excellent hydrogen storage performance, releasing hydrogen at 239.5 °C with a capacity of 6.17 wt%. At 300°C, the composite released 5.72 wt% H₂ within 15 min, while hydrogen absorption commences at room temperature. Notably, after 100 cycles of hydrogenation/dehydrogenation, the capacity retention was maintained at 99.98 %, underscoring its exceptional cycling stability. The measured dehydrogenation activation energy was reduced to 85.38 kJ/mol, approximately 47.5 % lower than that of pure MgH 2 (162.54 kJ/mol). Mechanistic studies reveal that Nb 5 + is preferentially reduced and acts as a nucleation as well as growth site for Mg, allowing Mg to interact and distribute evenly with Nb. This structure not only provides abundant active sites and hydrogen diffusion pathways but also effectively suppresses the agglomeration and growth of Mg/MgH 2 matrix during hydrogenation/dehydrogenation. Furthermore, NbH 2 phases are formed during the hydrogenation/dehydrogenation process, significantly promoting the adsorption and dissociation of hydrogen atoms, thereby optimizing the hydrogen storage performance of the material.