Effect of phase formation on hydrogen storage properties in Ti-V-Mn alloys by zirconium substitution

In order to improve hydrogen storage properties of Ti₂₃V₄₀Mn₃₇ alloy with the two-phase mixture of BCC and C14 Laves, the alloys with different Zr (x = 0, 2, 4, 6, 8 and 10, at.%) partly substituting for Ti have been produced. The results show that the primary (dendrite) BCC phase decreases and C14 Laves phase increases with increasing Zr. The secondary (blocky) BCC phase appears when Zr content is more than 6 at.%. The hydrogen absorption rate increases after completely activated because the Zr improves the formation of C14 Laves phase. Meanwhile, the reversible hydrogen capacity of Zr-substituted alloys is higher than that of Zr-free alloy. The effective hydrogen storage capacity reaches the maximum when the composition is Ti₂₁Zr₂V₄₀Mn₃₇, with a value of 1.85 wt.% at 293 K. Two desorption plateaus appear when Zr content is more than 6 at.%, and the width of the higher plateau increases with increasing of Zr. The higher plateau results from the fast diffusion of H atom in the smaller secondary BCC phase. With increasing the Zr content, the hysteresis and plateau slope factor increase, which can be attributed to the increasing strain energy of interstitial sites and the affinity of interstitial sites with H.