Catalytic effect of in situ formed nano-Mg₂Ni and Mg₂Cu on the hydrogen storage properties of Mg-Y hydride composites

Two hydrides nanocomposites, consisting of MgH₂-Mg₂NiH₄-YH₂ and MgH₂-MgCu₂-YH₂ phases, were prepared by hydrogenation upon the melt-spun Mg₈₀Y₅Ni₁₅ and Mg₈₀Y₅Cu₁₅ amorphous alloys, respectively. The catalytic effect of nano-Mg₂Ni/Mg₂NiH₄ and Mg₂Cu/MgCu₂ particles on hydrogen storage properties of Mg-Y hydride composites have been studied. It is shown that the activated melt-spun Mg₈₀Y₅Ni₁₅ alloy exhibits higher hydrogen absorption capacity and faster hydriding/dehydriding kinetics than those of the activated melt-spun Mg₈₀Y₅Cu₁₅ alloy. The activated melt-spun Mg₈₀Y₅Ni₁₅ alloy absorbs about 4.2 wt% hydrogen in 10 min at 200 °C, and almost fully desorbs hydrogen within 5 min at 280 °C. In contrast, the activated melt-spun Mg₈₀Y₅Cu₁₅ alloy absorbs about 4 wt % of hydrogen in 2 h at 280 °C, and desorbs 3.7 wt% of hydrogen in 80 min at 300 °C. The apparent activation energy of dehydrogenation for the activated melt-spun Mg₈₀Y₅Ni₁₅ alloy was calculated to be 83.9 kJ/mol, which is significantly lower than that of 132.3 kJ/mol for the activated melt-spun Mg₈₀Y₅Cu₁₅ alloy. The excellent hydrogen storage properties of the activated melt-spun Mg₈₀Y₅Ni₁₅ alloy can be attributed to the multiple cracks and refined particle size generated during hydrogenation, and the uniform distributed catalytic Mg₂Ni/Mg₂NiH₄ nanoparticles in the Mg/MgH₂ matrix. In contrast, a large amount of Mg₂Cu/MgCu₂ phase significantly aggregations, and the separation between Mg₂Cu/MgCu₂ and Mg/MgH₂ matrix in the activated melt-spun Mg₈₀Y₅Cu₁₅ alloy, which greatly decrease the catalytic effect of Mg₂Cu for the activated melt-spun Mg₈₀Y₅Cu₁₅ alloy.