Rehydrogenation performance of an MgH_2-Nb_2O_5 system modified by heptane and acetone

摘要

An MgH_2 + 1 mol% Nb_2O_5 system was modified by heptane and acetone through a high-energy ball milling process, and their rehydrogenation performances were investigated. XRD results indicated that except MgH_2 and Nb_2O_5 phases Mg and MgO phases existed after ball milling. The rehydrogenation results showed that after modification by heptane the capacity increased from 3.0 wt% and 4.2 wt% to 5.0 wt% and 5.5 wt% within 110 s at 523 K and 573 K, respectively. The hydriding rate increased from 0.08 wt%/s after 20 s to 0.22 wt%/s after 10 s at 523 K. However, after modification by acetone it only absorbed 1.8 wt% and 2.0 wt% of hydrogen even within 8000 s at 523 K and 573 K, respectively. Rietveld refinement results indicated that after modification by the heptane the content of MgO was reduced from 6.8 wt% to 4.2 wt%, while after the modification by the acetone the content of MgO was significantly increased from 6.8 wt% to 23.8 wt%. The difference in the rehydrogenation performance was believed to be attributed to the different contents of the MgO phase, which led to the difference in the contents of the MgH_2 phase. It implied that the heptane acted as a solvent without oxygen element in it to prevent the MgH_2 + Nb_2O_5 system from aggregation, crystallization and oxidation. It suggested heptane was suitable for the improvement of the rehydrogenation performance of MgH_2 system.