Although Mg alloy-based hydrides have been considered as promising solid-state materials due to their high capacity and low cost, the high dehydrogenation temperature of ∼ 300℃ severely limited their practical application. Herein, a series of Mg-based quaternary alloys of Mg 85 Ni 5 Cu 5 M 5 (M = Al, Zn, Co, La) hydrides were prepared by a combination of meltspinning and ball milling process, demonstrating an efficient approach to promoting the hydrogen storage properties. Among them, the Mg 85 Ni 5 Cu 5 La 5 hydride (H-Mg 85 Ni 5 Cu 5 La 5 ) as the most excellent one starts to release hydrogen from 175℃, 125℃ lower than that of MgH 2 . Especially, the peak hydrogen release temperature of H-Mg 85 Ni 5 Cu 5 La 5 was remarkedly reduced from 347℃ to 253℃, compared with MgH 2 . Additionally, the H-Mg 85 Ni 5 Cu 5 La 5 presented an impressive initial hydrogen capacity of 4.2 wt% with a high-capacity retention of 92.6 % over 10 dehydrogenation cycles. In/Ex-situ XRD analyses proved that the synergistic effects of in-situ formed metallic Ni and LaH 2 catalytic phases during the milling and ab/desorption processes can simultaneously enhance the ab/desorption kinetics of Mg/MgH 2 . That is, the LaH 2 can act as a hydrogen pump to promote the dehydrogenation of hydrides, while the Ni is beneficial to accelerate the dissociation of metal-hydrogen atoms and the formation of hydrogen molecules on the surface of Mg alloy. These findings highlight the potential of multicomponent Mg-based alloys for practical use in solid-state hydrogen storage systems through in-situ formed catalytic phases.
The Mg-based hydrogen storage alloy with multiple platforms is successfully prepared by ball milling Co powder and Mg-RE-Ni precursor alloy, and its hydrogen storage behavior was investigated in detail by XRD , EDS , TEM, PCI , and DSC methods. The ball-milled alloy consists of the main phase Mg, the catalytic phases Mg 2 Ni, Mg 2 Co as well as a small amount of Mg 12 Ce, and convert into the MgH 2 –CeH 2.73 -Mg 2 NiH 4 –Mg 2 CoH 5 composite after hydrogenation. The composite has three PCI platforms corresponding to the reversible de/hydrogenation reaction of Mg/MgH 2 , Mg 2 Ni/Mg 2 NiH 4 and Mg 6 Co 2 H 11 /Mg 2 CoH 5 . Among them, the transformation between Mg 2 Ni and Mg 2 NiH 4 triggers the “spill-over” effect which promote the decomposition of MgH 2 phases and enhances the hydrogen desorption kinetics. Meanwhile, the conversion of the Mg 6 Co 2 H 11 to Mg 2 CoH 5 phase induces the “chain reaction” effect, which leads to preferential nucleation of Mg phase and improves the hydrogen absorption kinetics. Therefore, the Mg-RE-Ni-Co alloy has a double improvement on hydrogen absorption and desorption kinetics. Concretely, the alloy has an optimal hydrogen absorption temperature of 200 °C, at which it can absorb 5.5 wt. % H 2 within 40 s. Under the conditions, the capacity of absorption almost reaches the maximum reversible value (about 5.6 wt. %). Besides, the alloy has a dehydrogenation activation energy of 67.9 kJ/mol and can desorb 5.0 wt. % H 2 within 60 min at the temperature of 260 °C.
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