Effect of (Ti_0.35V_0.65)_0.86Fe_0.14H_y on synthesis and hydrogen storage properties of NaAlH₄

The (Ti_0.35V_0.65)_0.86Fe_0.14H_y powder was prepared by melting, annealing and H₂-assisted-crushed method to avoid passivation. Then [(Ti_0.35V_0.65)_0.86Fe_0.14H_y]_x/100-NaAlH₄ composite system were synthesized using a two-step in-situ-milling method with the proportion of n (NaH):n (Al):n (Graphene):n (alloy) = 100:100:5:x (x = 2,5,8). It was found that lattice distortion had occurred on the alloy after 190hindividually milling, and the hydrogen storage capacity had decreased significantly to 1.10 wt%. However, after long-term composite milling, the alloy could still reduce the hydrogen pressure required for the synthesis of NaAlH₄, besides it could effectively reduce the hydriding/dehydriding temperature and improve the kinetic properties. This may due to the alloy's ability to dissociate H₂ and transfer H at room temperature, thereby enhancing the opportunity for direct contact between the matrix and H. In this study, x = 5 was the optimal alloy addition ratio, its dehydrogenation capacity at the 1st cycle reached 5.04 wt%; and at the 2nd and subsequent cycles, it remained rather stable at 4.40 wt%.