Hydrogen storage properties of (Ti_0.85Zr_0.15)_1.05Mn_1.2Cr_0.6V_0.1M_0.1 (M=Ni, Fe, Cu) alloys easily activated at room temperature

The (Ti_0.85Zr_0.15)_1.05Mn_1.2Cr_0.6V_0.1M_0.1 (M=Ni, Fe, Cu) alloys with a single C14-type Laves phase have been fabricated by arc melting. They are able to be easily activated by one hydrogen absorption and desorption cycle under 4 MPa hydrogen pressure and vacuum at room temperature. Partial substitution of M for Mn results in the increase of hydrogenation and dehydrogenation capacities in an order of Ni < Fe < Cu. M elements increase the absorption and desorption plateau pressure in an order of (Ti_0.85Zr_0.15)_1.05Mn_1.2Cr_0.6V_0.1Cu_0.1 < (Ti_0.85Zr_0.15)_1.05Mn_1.2Cr_0.6V_0.1Fe_0.1 < (Ti_0.85Zr_0.15)_1.05Mn_1.2Cr_0.6V_0.1Ni_0.1. The (Ti_0.85Zr_0.15)_1.05Mn_1.2Cr_0.6V_0.1Cu_0.1 alloy has reversible hydrogen capacities of 1.81 wt% at 273 K and 1.58 wt% at 318 K with formation enthalpy (ΔH_ab) of −20.66 kJ mol⁻¹ and decomposition enthalpy (ΔH_de) of 27.37 kJ mol⁻¹. The differences in the hydrogen storage properties can be attributed to the increase of the interstitial size for hydrogen accommodation caused by the increase of unit cell volumes in the order of (Ti_0.85Zr_0.15)_1.05Mn_1.2Cr_0.6V_0.1Ni_0.1 < (Ti_0.85Zr_0.15)_1.05Mn_1.2Cr_0.6V_0.1Fe_0.1 < (Ti_0.85Zr_0.15)_1.05Mn_1.2Cr_0.6V_0.1Cu_0.1.