Influence of the phase evolution and hydrogen storage behaviors of Mg-based alloy catalyzed by Gd-Fe compound

Abstract

In order to further optimize the kinetic and thermal properties of Mg-based hydrogen storage alloy, the Mg + 10 wt% GdFe alloy is prepared by using vacuum induction melting. The XRD, SEM, EDS, TEM, PCT and TG-DTA are used to characterize the microstructure of the alloy and phase transition in the reaction process. The results show that the sample is composed of the main phase Mg and the remaining Mg5Gd. In addition, Fe elements are evenly distributed in dissolved in the Mg matrix. After hydrogen absorption, all these phases disappear and are transformed into MgH2 and GdH2. After hydrogen desorption, MgH2 transforms to Mg phase, but the GdH2 phase remains unchanged. During the reaction, Fe always exists in the Mg/MgH2 lattice in the form of simple substance, which is beneficial to the recombination and dissociation of hydrogen atoms. Meanwhile, the GdH2 phase also provides abundant the active sites and diffusion admittance. The alloy has a reversible hydrogen content of 5.8 wt% H2 and an activation energy of 144.1 kJ/mol. It also shows excellent kinetic properties, which can absorb 4.3 wt% H2 at 360 °C in 10 min, and complete hydrogen desorption at the same temperature requires only 18 min. The thermodynamics energy increases only slightly, but the initial hydrogen release temperature and peak temperature are much lower than those of Mg.