Unleashing Superior Hydrogen Storage of Magnesium Hydride via Vanadium-Doped Bimetallic MXene

Magnesium hydride (MgH₂) has been recognized as a promising hydrogen storage material because of its low cost and high hydrogen capacity. However, the sluggish kinetics and high operating temperature hindered its utilization. Herein, vanadium-substituted titanium-based bimetallic MXene (Ti_3-<i>n</i>V_<i>n</i>C₂) was prepared to boost the hydrogen storage efficiency of MgH₂. The incorporation of 5 wt % Ti_2.2V_0.8C₂ dramatically decreased the dehydrogenation temperature of MgH₂ and improved its kinetics and cyclic stability. The MgH₂-5 wt % Ti_2.2V_0.8C₂ started to release hydrogen at 165 °C, and it released 7.0 wt % H₂ in 30 min at 220 °C and took in 5.3 wt % H₂ in 2 h at 75 °C, showing excellent kinetics. In addition, the activation energy of MgH₂-added Ti_2.2V_0.8C₂ was 80.81 ± 3.29 kJ mol^-1, which is lower than that of the most Ti-/or V-based catalyst-doped MgH₂ systems. Mechanism analysis reveals that the remarkably enhanced hydrogen storage performance is ascribed to the stable existence and uniform distribution of Ti-species (Ti⁰ and Titanium hydride) and V-species (V⁰ and V⁵⁺), which facilitated the rapid hydrogen absorption/desorption of MgH₂ and ensured its stable hydrogen storage capacity. This study offers valuable perspectives for the assembly and design of bimetallic catalysts within the realm of solid-state hydrogen storage materials.