Effect of Hafnium Addition on the Hydrogenation Process of TiFe Alloy

Abstract

The alloy TiFe has interesting hydrogen storage properties for practical applications: low cost, operation at room temperature, and good hydrogen capacity. However, the first hydrogenation is difficult and increases the cost of the alloy. In this work, we studied the effect of adding hafnium to TiFe in order to enhance the first hydrogenation process. TiFe + x Hf alloys, with x = 0, 4, 8, 12, and 16 wt.%, were synthesized by arc melting. The microstructure of the as-cast alloys was investigated by scanning electron microscopy and electron microprobe analysis. These alloys consisted of B2-TiFe, C14-Laves, and BCC (Body Centered Cubic) phases. A minimum of 8 wt.% of hafnium is required to obtain an enhancement of the first hydrogenation. In the first hydrogenation, the material reaches its maximal hydrogen capacity in less than two hours at room temperature and under 20 bars of hydrogen. Hafnium addition also had the effect of lowering the plateau pressure in the pressure-composition isotherm. It could be concluded that hafnium has a positive effect on the activation properties of TiFe.

Substitutional effects in TiFe for hydrogen storage: a comprehensive review

“…The formation of secondary phases have also been observed, improving activation (possible at room temperature and 20 bar) and kinetics, but slightly reducing the hydrogen capacity of the material. [121] Vanadium (V, rV= 0.1316 nm) can substitute both Ti and Fe in TiFe. [104,122] Furthermore, it has been reported that the addition of V to TiFe0.90 decreases the total capacity of the material, but on the other hand it decreases hysteresis between absorption and desorption, even if slopped plateaus are observed.…”

“…Hafnium (Hf, r Hf = 0.15775 nm) can be introduced into TiFe up to 2 at.%, causing an increase of the cell parameter and a subsequent decrease of plateau pressures. The formation of secondary phases have also been observed, improving activation (possible at room temperature and 20 bar) and kinetics, but slightly reducing the hydrogen capacity of the material [121].…”