Hydrogen is an attractive energy source in terms of prevalence, environmental friendliness and energy efficiency with its participation. The development of hydrogen energy is limited by the problems of storage and transportation of hydrogen. Binary alloy TiFe is suitable for storage for hydrogen storage. This alloy is known to have a high ability to absorb hydrogen with a ratio of hydrogen atoms (H) to metal atoms (M) H/M is near 1 and also fast absorption/desorption kinetics at ambient conditions. The low cost of the starting materials is also important for practical application. However, a lot of research still needs to be done to identify appropriate catalysts, study the existence of stable intermediate phases and their crystal structure, and understand the kinetics.

Consider the interaction and crystal structure of Fe-H, Ti-H and Ti-Fe-H. It is known that hydrogen has a low interaction with iron. At the same time, both the solid solution and FeH hydride are possible. At ambient temperature, α-Fe dissolves 0.005% of hydrogen with the BCC lattice a = 2.8590 Å. Hydrogen interacts well with titanium, forming the solid solution in a wide range. With increasing temperature, the mass fraction of hydrogen increases. This process is reversible, so titanium can be used to store hydrogen. Also, hydrogen is the stabilizer of the β-phase, which leads to the decrease in the temperature of the α↔β transformation of titanium. When the concentration of hydrogen increases to 4.04 wt %, the stable ТН₂ hydride is formed.

Let us consider TiFe alloys. They are able to absorb and desorb hydrogen. Hydrogenation processes is accompanied by an order-disorder phase transition from the CsCl-type structure to the BCC of TiFe metal lattice at high pressure and temperature. We observed lattice expansion of the sample when the TiFe alloy was kept in hydrogen fluid at 5 GPa and 600 °C. The lattice parameter of the sample before the hydrogenation experiment was a = 2.979 Å. At the first stageofhydrogenation the lattice parameter of the solid solution changed to a = 2.961 Å. After 60 min the hydrogenation treatment it is formed new cubic phase and the lattice parameter increased to a = 3.132 Å. After 150 min the hydrogenation treatment when the lattice increased to maximum, the hydride decomposed into TiH₂ hydride and TiFe alloy. Hydrogenation processes at 10 GPa and 600 °C were similar like at 5 GPa and 600 °C. Due to the property of titanium to form TiH₂ hydride, the partial substitution of iron (Fe) in TiFe alloys with manganese (Mn), nickel (Ni), chromium (Cr) and vanadium (V) has been proven to facilitate the activation and decrease the equilibrium pressure of the final hydrides but does not change the hydrogen storage capacity.

The sintering of TiH₂ and Fe by thermocycling at temperatures near the α↔β transformation of Fe did not give the desired result. The X-ray pattern showed the existence of two separate phases TiH₂ and Fe, which may indicate the stability of the TiH₂ hydride in the TiFe alloy.

Conclusion. TiFe alloys are attractive for their ability to absorb large amounts of hydrogen. Hydrogenation processes are accompanied by an order-disorder phase transformation. However, the use of TiFe hydrides is limited, because when the hydrogen concentration increases to 4.04 wt % H, the stable TiH₂ hydride is formed. Partial replacement of doped elements can improve hydrogenation kinetics without changing its ability to store hydrogen. Changing the pressure from 5 GPa to 10 GPa at temperature of 600 °C does not affect hydrogenation processes.