Abstract
Transition metals and rare-earth elements have excellent catalytic effects on improving the de-/hydrogenation properties of Mg-based alloys. In this study, a small amount of La is used to substitute the Ni in Mg98Ni2 alloy, and some Mg98Ni2-xLax (x = 0, 0.33, 0.67, and 1) alloys show the better overall hydrogen storage properties. The effects of La on the solidification and de-/hydrogenation behaviors of the alloys are revealed. The results indicate that different factors dominate the processes of hydrogen absorption and desorption. The Mg98Ni1·67La0.33 alloy absorb 7.04 wt % hydrogen at 300 °C, with the highest isothermal absorption rate, the Mg98Ni1·33La0.67 hydride show the highest isothermal desorption rates and the lowest peak desorption temperature of 327 °C. The La addition can increase the driving force of hydrogenation, thus the hydrogenation rates and capacities of the Mg98Ni1·67La0.33 and Mg98Ni1·33La0.67 alloys are improved. The formation of refined eutectic structures is a key factor that facilitates the desorption processes of the Mg98Ni2-xLax hydrides with x = 0.67 and 1. High-density LaH3 nanophses are in-situ formed from the LaMgx (8.5 < x < 12) phase, which results in the improved de-/hydrogenation properties. The further La addition deteriorates the hydrogen storage properties of Mg98Ni2-xLax alloy.
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