Co-effects of Tm_2O_3 and porous silica on reversible hydrogen storage in NaAlH_4

摘要

The co-effects of lanthanide oxide Tm__2O3 and porous silica on the hydrogen storage properties of sodium alanate are investigated. NaAlH_4-Tm_2O_3 (10 wt%) and NaAlH_4-Tm_2O_3 (10 wt%)-porous SiO_2 (10 wt%) are prepared by the ball milling method, and their hydrogen desorption/re-absorption capacities are compared. Dehydrogenation process was performed at 150 ℃under vacuum and rehydrogenation was performed at 150 ℃ for 4 h under ~9 Mpa in highly pure hydrogen. The results show that Tm_2O_3 has a catalytic effect on the hydrogen desorption and re-absorption of NaAlH_4. The hydrogen desorption capacity of Tm_2O_3 single-doped NaAlH_4 is 4.6 wt%, higher than that of undoped NaAlH_4 (4.3 wt%). During the dehydrogenation process, NaAlH_4 is completely decomposed and no intermediate product Na_3AlH_6 is detected. The addition of porous silica improves the dehydrogenation performance of NaAlH_4. Tm_2O_3 and porous silica co-doped NaAlH_4 could release a maximum hydrogen amount of 4.7 wt%, higher than that of undoped NaAlH_4 and Tm_2O_3 single-doped NaAlH_4. Moreover, porous silica improves the reversibility of hydrogen storage in NaAlH_4.