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In this paper, the as-cast and extruded Mg-4.7Y-4.1Nd-0.5Zr alloys were prepared, and their microstructures, hydrogen storage properties and catalytic mechanisms were systematically studied. The results show that the as-cast Mg-4.7Y-4.1Nd-0.5Zr alloy is mainly composed of Mg, Mg 24 Y 5 and Mg 41 Nd 5 phases, while the Mg 41 Nd 5 phase in the extruded alloy is dissolved into Mg matrix due to homogenization. After hydrogenation, the in - situ formed nano-particles of rare earth hydride REH x are uniformly distributed on the surface of MgH 2 , which exhibit remarkable catalytic effects on the subsequent hydrogenation and dehydrogenation of Mg matrix. According to the isothermal hydrogen absorption and desorption kinetic testing, the Mg-4.7Y-4.1Nd-0.5Zr alloys in the two states both exhibit good hydrogen sorption kinetics. Compared with pure Mg, the apparent activation energies of dehydrogenation reaction of the as-cast and extruded alloys are reduced to 114 kJ mol−1 H 2 and 109 kJ mol−1 H 2 , respectively, which should be ascribed to the catalytic roles of YH 2 and NdH 2 nano-hydrides. Comparatively, the extruded alloy presents a more excellent dehydrogenation kinetics, and it can release more than 6 wt% of hydrogen within 15 min at 350 °C. First-principles calculations reveals that the rare earth hydrides YH 2 and NdH 2 improve the hydrogen storage performance of Mg alloy by weakening the bonding strength of the H–H bond within H 2 molecule and the Mg–H bond within MgH 2. • The as-cast and extruded Mg-4.7Y-4.1Nd-0.5Zr alloys were prepared. • The alloys in-situ form RE (Y / Nd)H x (x = 2,3) hydrides after hydrogenation. • The RE (Y/Nd)H x (x = 2,3) hydrides exhibit catalytic effects on Mg matrix. • The dehydrogenation rate of extruded alloy is faster relative to as-cast alloy. • The YH 2 and NdH 2 both weaken the bond strength of H–H within H 2 and Mg–H with MgH 2. [ABSTRACT FROM AUTHOR]

In this work, three different states of Mg-9.1Y-1.8Zn alloys including as-cast, extruded and swaged were prepared by semi-continuous casting, extrusion and swaging processes, respectively. Their compositions, microstructures and hydrogen storage properties were investigated. The results show that Mg-9.1Y-1.8Zn alloys in three different states are all composed of Mg and long-period stacking ordered (LPSO) phases. The LPSO phases occurs to break and decompose after hydrogenation and in-situ forms the YH χ(χ = 2,3) nano-hydrides. The nano-hydrides can be used as in-situ catalysts to improve the hydrogen storage properties of alloys. Meanwhile, many nanocrystalline grains appear in the core of alloy after swaging, and the average grain size ranges from 80 to 200 nm. The presence of nanocrystals may increase the specific surface area of alloy, facilitating the diffusion and absorption of hydrogen. Comparatively, the swaged alloy exhibits the largest hydrogen storage capacity and excellent hydrogen sorption kinetics relative to other states of alloys. • The as-cast, extruded, and swaged Mg-9.1Y-1.8Zn alloys were prepared. • The LPSO phases decomposes and in-situ forms YH χ(χ = 2,3) hydrides upon hydrogenation. • The YH χ(χ = 2,3) hydrides present in-situ catalytic and pinning effects on Mg matrix. • The swaged alloy exhibits the highest hydrogen storage capacity. [ABSTRACT FROM AUTHOR]

In this work, the as-cast Mg-rich Mg 98.5 Gd 1 Zn 0.5 and Mg 98.5 Gd 0.5 Y 0.5 Zn 0.5 alloys are prepared by the semi-continuous casting method, and their hydrogen storage performance and catalytic mechanisms are investigated by experimental and first-principles calculations approaches. The results show that the LPSO phases decompose and in-situ form the RE(Gd/Y)H x (x = 2,3) nano-hydrides upon hydrogenation. These nano-hydrides not only serve as the in-situ catalysts to promote the hydrogen ab/desorption of Mg matrix, but also present the pinning effect to inhibit the growth of Mg / MgH 2 grains during hydrogenation and dehydrogenation. Comparatively, the two alloys exhibit the similar hydrogen absorption kinetics, while the hydrogen desorption kinetics of Mg 98.5 Gd 1 Zn 0.5 is superior to that of Mg 98.5 Gd 0.5 Y 0.5 Zn 0.5. The first-principles calculations reveal that the GdH 2 and YH 2 hydrides exhibit different catalytic effects on weakening the bond strength of H–H within H 2 and Mg–H within MgH 2 , which interprets well the differences in the hydrogen ab/desorption kinetics between Mg 98.5 Gd 1 Zn 0.5 and Mg 98.5 Gd 0.5 Y 0.5 Zn 0.5 alloys. • The Mg-rich Mg-Gd-Zn and Mg-Gd-Y-Zn alloys are prepared by semi-continuous casting. • The LPSO phases decompose and in-situ form RE(Gd / Y)H x (x = 2,3) upon hydrogenation. • The RE(Gd/Y)H x (x = 2,3) show in-situ catalytic and pinning effects on Mg alloys. • The desorption rate of Mg 98.5 Gd 1 Zn 0.5 is faster than that of Mg 98.5 Gd 0.5 Y 0.5 Zn 0.5. • The GdH 2 and YH 2 both weaken the bond strength of H–H within H 2 and Mg–H with MgH 2. [ABSTRACT FROM AUTHOR]