Optimizing Hydrogen Storage Pathways in Ti–Al Alloys through Controlled Oxygen Addition

Abstract

In the present study, we aimed to destabilize the Ti–Al system with nonmetallic oxygen. The synthesis of α‐(Ti, Al)[O] starting from TiO2, Ti, and Al was carried out through the arc melting method, resulting in three different oxygen content levels, 3.4, 10, and 20 at%. The room temperature activation of α‐(Ti, Al)[O] was not successful, and the activation was performed at 300°C under 5 MPa H2 pressure. The structural changes after hydrogenation (maximum absorption capacity of 3.74 wt% hydrogen) arose from the transformation of α‐(Ti, Al)[O] to cubic (Ti, Al)[O]Hx (c‐(Ti, Al)[O]Hx); nonetheless, they recovered their original lattice parameters, which are meaningfully larger than those of α‐Ti, after dehydrogenation. The hydrogen storage capacities for various α‐(Ti, Al)[O] compositions generally decreased with increasing oxygen (3.4 and 10 at%) and aluminum content in the alloy. In contrast, for the compositions with a higher oxygen content of 20 at%, the hydrogen storage capacity slightly increased as the Al concentration increased: Ti0.790Al0.010O0.200 absorbed 2.91 wt% hydrogen, whereas Ti0.767Al0.033O0.200 absorbed 3.04 wt% hydrogen. The thermogravimetric analysis showed that samples with 20 at% O released hydrogen at lower temperatures even though the major phase after hydrogenation is c‐(Ti, Al)[O]Hx regardless of the oxygen content.