Hot extrusion-induced Mg-Ni-Y alloy with enhanced hydrogen storage kinetics

In this work, the influence of the hot-extrusion method on the hydrogen storage kinetics of Mg-Ni-Y alloy was investigated. It was shown that the extruded Mg91.47Ni6.97Y1.56 alloy exhibits improved hydriding and dehydriding (H/D) kinetics, with a capacity of 3.5 wt.% H2 absorption within 60 s and 5.4 wt.% H2 desorption within 5 min at 573 K. The dehydrogenation activation energy of extruded alloy is 71.4 kJ mol−1, smaller than that of as-cast alloy (140.5 kJ mol−1). The enhancement of H/D kinetics is attributed to the microstructural refinement and increased grain/phase boundaries introduced by hot extrusion, as well as the catalytic effects from the in-situ generated and grain-refined Mg2Ni and YH2 particles during the H/D process. Furthermore, the dehydrogenated rate-determining step transforms from hydrogen diffusion in the hydride (as-cast alloy) to the surface penetration of hydrogen atoms (extruded alloy). These findings provide crucial insights for the design of Mg-based hydrogen storage alloys in the future.