Co-effects of Tm2O3 and porous silica on reversible hydrogen storage in NaAlH4

The co-effects of lanthanide oxide Tm₂O₃ and porous silica on the hydrogen storage properties of sodium alanate are investigated. NaAlH₄-Tm₂O₃ (10 wt%) and NaAlH₄-Tm₂O₃ (10 wt%)-porous SiO₂ (10 wt%) are prepared by the ball milling method, and their hydrogen desorption/re-absorption capacities are compared. Dehydrogenation process was performed at 150 °C under vacuum and rehydrogenation was performed at 150 °C for 4 h under ∼9 MPa in highly pure hydrogen. The results show that Tm₂O₃ has a catalytic effect on the hydrogen desorption and re-absorption of NaAlH₄. The hydrogen desorption capacity of Tm₂O₃ single-doped NaAlH₄ is 4.6 wt%, higher than that of undoped NaAlH₄ (4.3 wt%). During the dehydrogenation process, NaAlH₄ is completely decomposed and no intermediate product Na₃AlH₆ is detected. The addition of porous silica improves the dehydrogenation performance of NaAlH₄. Tm₂O₃ and porous silica co-doped NaAlH₄ could release a maximum hydrogen amount of 4.7 wt%, higher than that of undoped NaAlH₄ and Tm₂O₃ single-doped NaAlH₄. Moreover, porous silica improves the reversibility of hydrogen storage in NaAlH₄.