Effect of Fe addition on hydrogen storage characteristics of Ti_0.16Zr_0.05Cr_0.22V_0.57 alloy

The effect of Fe addition on hydrogen storage characteristics of Ti_0.16Zr_0.05Cr_0.22V_0.57 alloy has been studied at 303 K. The X-ray diffraction (XRD) patterns of the alloy powders showed the typical patterns of BCC structure as a main phase in all of the alloys. With increasing Fe content, the lattice parameters of the BCC phases decreased linearly in accordance with Vegard's law. With regard to the maximum hydrogen storage capacities of the alloys, there was a noticeable decrease between alloys that contained 3 and 5 at% of Fe. The reason for this can be deduced from three factors: the decrease in the lattice parameter of BCC phase, the decrease of the amount of BCC phase itself in the alloy, and the excess of the electron-to-atom ratio over 5.1 (5.09 at 3 at% Fe and 5.16 at 5 at% Fe) with increasing Fe content. The Fe addition remarkably increased the second plateau pressures in the pressure composition (P-C) isotherms. However, the first plateau was not observed in all the alloys under the conditions of the present study. From the relation between the hydrogen storage capacities and the lattice parameters of the alloys, it was found that controlling the lattice parameter similarly to that of V (3.03 angstrom), i.e. within the range of about 3.02-3.04 angstrom, is of fundamental importance to obtain the largest effective hydrogen storage capacity in this alloy systems under the present conditions.