Microstructures and hydrogen storage properties of Mg-Y-Zn rare earth magnesium alloys with different Zn content: Experimental and first-principles studies

Abstract

In this work, as-cast Mg-9.1Y-1.0Zn, Mg-9.1Y-1.8Zn and Mg-9.2Y-3.1Zn (wt%) alloys with different Zn content are prepared by the semi-continuous casting method. The microstructures and hydrogen storage properties are systematically investigated by experimental and first-principles calculations approaches. The results show that more LPSO phases form with increasing Zn content and they mainly distribute at the grain boundaries of alloys. The LPSO phases decompose and in-situ form YH2/YH3 hydrides upon hydrogenation. These YH2/YH3 hydrides are more likely to be concentrated at the grain boundaries with increasing Zn content, which leads to the non-uniform distribution of YH2/YH3 hydrides in these alloys. The more non-uniform distribution of these YH2/YH3 hydrides on the Mg matrix will lead to the worse hydrogen storage performance of alloys. Comparatively, the three alloys exhibit similar hydrogen absorption kinetics, while the as-cast Mg-9.1Y-1.0Zn (wt%) shows the best hydrogen desorption kinetics. First-principles calculations show that the H removal energies Erom and H2 recombination energies Erecom from MgH2(110) surface both decrease upon the role of YH2, which further validates the catalytic effect of YH2 on hydrogen sorption kinetics of Mg-Y-Zn alloys.