Activation of Long-Time Placed TiMn-based AB2-type Alloy by Co-Doping of LaNi5 and V for Hydrogen Storage

TiMn-based AB2-type hydrogen storage alloy with low cost, relatively suitable platform pressure, and high hydrogen storage capacity, stands out as one of the most promising candidates for practical applications in hydrogen storage. However, the TiMn-based alloy gradually losses activity, especially during prolonged exposure to air, posing challenges for activation and greatly increasing the operation cost in large-scale application. The LaNi5 alloy exhibits excellent initial activation performance, making it an ideal additive to enhance the initial reaction kinetics of TiMn-based AB2-type alloy. Nevertheless, the introduction of LaNi5 tends to reduce the hydrogen storage capacity of the mother alloy. Vanadium (V) possesses a relatively high hydrogen storage capacity (3.8 wt.%), and its addition can enhance the hydrogen storage capacity of the mother alloy. In this study, we employ a co-doping strategy, using 5 wt.% of LaNi5 and 5 wt.% of V, to activate an inactive TiMn-based AB2type alloy (placed for 1 year in air). This approach not only enhances the initial reactivity of the TiMn-based mother alloy but also restores its high-capacity performance. At 303 K and 6 MPa H2 pressure, the co-doping alloy (90 wt.% TiMn-based alloy - 5 wt.% LaNi5 - 5 wt.% V) demonstrates a substantial increase in initial hydrogen absorption rate, achieving a hydrogen absorption capacity of 1.61 wt.% in 6 min. The maximum hydrogen absorption capacity reaches 2.00 wt.% in 90 min. After 5 and 20 cycles, it maintains a reversible capacity of 1.55 and 1.45 wt.%, respectively. The outstanding hydrogen storage performance is attributed to the formation of multiphase alloys, as evidenced by X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) measurements. The reaction enthalpy (Delta H) of the co-doping alloy is calculated as 34.1 kJ/(mol H2), a value suitable for operation at room temperature. This work supplies an efficient strategy for the activation of long-time placed inactive hydrogen storage alloys and the enhancement of their hydrogen storage performance, and avoids the waste of raw materials due to inactivation in air. The achievements shed lights on the regeneration of inactive alloys and the cost control in the case of large-scale application of solid hydrogen storage alloys.