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.
Highlights
Iron is one of the most abundant element in the Earth crust, and titanium is obtained at low cost
The crystallite size remains the same independent of hafnium content
The activation process of TiFe alloy could be enhanced without any heat treatment and without decreasing the hydrogen absorption capacity drastically by casting with addition of atand least
Summary
Iron is one of the most abundant element in the Earth crust, and titanium is obtained at low cost This makes the TiFe alloy relatively inexpensive and an auspicious material for solid-state hydrogen storage. Several studies showed that forming a nanocrystalline TiFe compound at room temperature by mechanical alloying could improve the activation process [11,12,13,14]. Most of these studies demonstrated the importance of a third element and a strong relationship between the synthesis, the microstructure, and the hydrogen sorption of the TiFe alloy. It could be incorporated in the TiFe crystal structure in solid solution
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