The catalysis of Dy2O3 for RE-Mg based alloys hydrogen storage performance

The study used ball-milling to create composites of Mg90Ce5Y5 with various amounts of Dy2O3 catalyst (0, 2, 4, 6, 8 wt. %). The structures of samples were analyzed and it was found that the hydrogen storage mechanism involved the reactions: Mg + H2 ↔ MgH2 and DyH2 + H2 ↔ DyH3, and the stable phases CeO2, YH2, and DyH2 did not react. The catalyzed samples had better kinetics performance compared to the uncatalyzed ones. At 473 K, the composite with 8 wt. % catalyst absorbed 78.6% of the maximum hydrogen storage in 2 min, compared to 64.7% for Mg90Ce5Y5 alone, and desorbed 3 wt. % H2 in 49 min, 60% faster than Mg90Ce5Y5 (122 min). The Edes of hydrogen desorption for the 4 wt. % Dy2O3 catalyzed sample was reduced from 129.2 ± 1.2 to 102.2 ± 1.5 kJ/mol. There is no significant improvement in thermodynamic properties, with ΔH decreasing only slightly from 80.7 ± 1.8 to 76.0 ± 1.6 kJ/mol H2 because the presence of the extra reversible reaction. The outstanding kinetics of the Dy2O3 catalyzed samples is due to the in-situ formation of DyH2/DyH3, which provides more lattice imperfections, rich phase compositions and fine grains to improve diffusion and nucleation.