Dehydrogenation behavior and mechanism of LiAlH4 adding nano-CeO2 with different morphologies

Abstract

Complex hydride LiAlH4, as a hydrogen storage material, possesses high theoretical hydrogen storage capacity (10.5 wt.%). However, highly efficient additives are urgently required to modify its thermal stability and sluggish kinetics. Some additives exhibit unique morphology-dependent characteristics. Herein, the efficient rare earth oxide nano-CeO2 additives with different morphologies (nanoparticles, nanocubes, and nanorods) are prepared by the hydrothermal method, and the intrinsic properties are characterized. The three different morphologies of nano-CeO2, which are different in the Ce3+ content and specific surface area, are added to LiAlH4 to improve the dehydrogenation behavior. The LiAlH4-CeO2-nanorod composite exhibits the optimal dehydrogenation behavior, which begins to desorb hydrogen at 76.6 °C with a hydrogen capacity of 7.17 wt.%, and 3.83 wt.% hydrogen is desorbed within 30 min at 140 °C. The dehydrogenation process of the composites demonstrates that hydrogen release is facilitated by the in-situ formed CeH2.73 and the facile transition between the oxidation states of Ce4+ and Ce3+. Combined with density functional theory calculations, the addition of nano-CeO2 can weaken the Al-H bond and accelerate the decomposition of [AlH4]4− tetrahedron, which is consistent with the reduction of the decomposition activation energy.