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.