Design of V-Substituted TiFe-Based Alloy for Target Pressure Range and Easy Activation

Titanium iron (TiFe) alloy is a room-temperature hydrogen-storage material, and it absorbs hydrogen via a two-step process to form TiFeH and then TiFeH₂. The effect of V addition in TiFe alloy was recently elucidated. The V substitution for Ti sublattice lowers P₂/P₁ ratio, where P₁ and P₂ are the equilibrium plateau pressure for TiFe/TiFeH and TiFeH/TiFeH₂, respectively, and thus restricts the two-step hydrogenation within a narrow pressure range. The focus of the present investigation was to optimize the V content such that maximum usable storage capacity can be achieved for the target pressure range: 1 MPa for absorption and 0.1 MPa for desorption. The effect of V substitution at selective Ti or Fe sublattices was closely analyzed, and the alloy composition Ti₄₆Fe_47.5V_6.5 displayed the best performance with ca. 1.5 wt.% of usable capacity within the target pressure range. At the same time, another issue in TiFe-based alloys, which is a difficulty in activation at room temperature, was solved by Ce addition. It was shown that 3 wt.% Ce dispersion in TiFe alloy imparted to it easy room-temperature (RT) activation properties.