Abstract:

Lithium alanate (LiAlH₄) is considered a promising solid-state hydrogen storage material due to its high theoretical hydrogen capacity (mass fraction about 10.5%). However, its practical application is hampered by high decomposition temperatures and sluggish kinetics. Titanium dioxide (TiO₂) has shown potential as an effective catalyst for improving the dehydrogenation properties of hydrides. Nevertheless, the catalytic performance of commercial TiO₂ is often limited by its uncontrollable morphology and structure. To overcome this limitation, this study used the Sol-Gel method to synthesize nanostructured TiO₂ catalysts with high specific surface area and abundant defects. The as-prepared TiO₂ was ball-milled with LiAlH₄ at different mass ratios (1%, 3%, 5%, and 7%) to form composites, whose dehydrogenation properties were systematically investigated. Results demonstrated that the 5% (in mass) TiO₂-doped sample exhibited optimal performance, lowering the onset dehydrogenation temperature of LiAlH₄ to 112 ℃, which is 53 ℃ lower than that of pristine LiAlH₄ (165 ℃). Under isothermal conditions at 200 ℃, the composite released a total hydrogen capacity of 7.84% (in mass) within a significantly shorter time, and completed dehydrogenation approximately 30 min faster than the undoped sample. Even at a lower temperature of 150 ℃, the doped sample released 4.64% (in mass) hydrogen, far exceeding the capacity of pure LiAlH₄ (<1% (in mass)) at the same temperature. Kinetic analysis revealed that TiO₂ doping reduced the activation energy for the first dehydrogenation step from 116.2 kJ/mol to 55.6 kJ/mol, a remarkable decrease of 52%. In-situ formation of active AlTi and LiAl intermediate phases during dehydrogenation played a critical role, which served as efficient catalytic centers, providing new pathways for hydrogen recombination and desorption. This work not only verifies that TiO₂ synthesized via the Sol-Gel method can effectively break through the performance ceiling of commercial catalysts, but also offers new insights and experimental basis for designing next-generation high-performance catalysts for hydrogen storage materials.

Key words: LiAlH₄, TiO₂, doping, hydrogen release property, reaction activation energy