Study on hydrogen storage property of (ZrTiVFe)xAly high-entropy alloys by modifying Al content

(ZrTiVFe)_xAl_y high-entropy alloys are potential hydrogen storage materials because of their intermediate properties of high hydrogen uptake capacity and fast kinetics. In this study, equimolar and non-equimolar (ZrTiVFe)₈₀Al₂₀ and (ZrTiVFe)₉₀Al₁₀ alloys were prepared, and the effect of Al content on the microstructure, element distribution, and hydrogen storage properties of (ZrTiVFe)_xAl_y alloys were investigated. The results show that both alloys are composed of C14 Laves phase, a small amount of tetragonal and HCP phases. With the increase of Al content, the content and the size of C14 Laves phase decrease, the V element content in C14 Laves phase also decreases, which is resulted from the contents of Zr, V, and Fe element constituting the C14 Laves phase decrease. The Ti element can combine with the excessive Al to form a tetragonal phase around the C14 phase, and the growth of the tetragonal phase causes the refinement of the C14 phase. The (ZrTiVFe)₉₀Al₁₀ alloy absorbed 1.3 wt. % H at room temperature, which indicates the better hydrogenation capacity and kinetics. The improvement of hydrogen storage property is resulted from the increased C14 Laves phase, more V element in C14 Laves phase and the severe lattice distortion of (ZrTiVFe)₉₀Al₁₀ alloy. It is found that the (ZrTiVFe)₈₀Al₂₀ alloy can be activated easily with only three cycles, which is caused by the refined Laves phase. After hydrogenated, H atoms are dissolved into the lattice space of C14 Laves phase for both alloys, and crystalline structure is not changed.