Effects of Ti/Mn ratio on microstructure and hydrogen storage properties of Ti-V-Mn alloys

Highlights: • The lattice parameter of BCC phase increases with increasing Ti/Mn ratio. • Faster hydrogen absorption results from the large lattice parameter that favors the diffusion of hydrogen atoms. • The hydrides are more stable in the alloys with higher Ti/Mn ratio. • Absorbing capacity strongly depends on e/a and lattice parameter. Hydrogen storage alloys based on V₃₅Ti_xMn_65-x (x = 20, 25, 30, 35 and 40) were prepared by non-consumable arc melting, and effects of Ti/Mn ratio on crystal microstructure and hydrogen storage properties have been investigated comprehensively. The results show that all alloys consist of the main body centered cubic (BCC) and C14 Laves phases. Both the lattice parameter and cell volume of BCC phase increase with increasing Ti/Mn ratio. The enlargement of the unit cells is in favor of atomic diffusion which leads to faster hydrogen absorption. The hydrides tend to be more stability with the increasing of Ti/Mn ratio. The hydrogen absorption capacity and effective hydrogen storage capacity reach the maximum for a composition of V₃₅Ti₃₅Mn₃₀, with values of 3.35 wt% at 293 K and 1.18 wt% at 303 K, respectively. It is also found that hydrogen absorption capacity strongly depends on the electron concentration ratio (e/a) and lattice parameters of BCC phase.