Influence of temperature and hydrogen pressure on the hydriding/dehydriding behavior of Ti-doped sodium aluminum hydride

A Ti-doped sodium aluminum hydride was prepared by ball-milling NaH/Al mixture with 10 mol% Ti powder under hydrogen for 12 h. The hydriding/dehydriding behaviors of the ball-milled sample under different temperatures (85–160 °C) and hydrogen pressures (7.5–13.5 MPa) were investigated. The results show that the hydriding/dehydriding temperature and hydrogen pressure affect the hydrogen storage behavior noticeably. During hydriding, under 13.5 MPa hydrogen pressure, as the hydriding temperature increases from 85 to 140 °C, the hydrogen absorption rate increases first and then decreases, and reaches the highest value at 120 °C. And the hydrogen absorption rate increases with the increase of hydrogen pressure all the way from 7.5 to 13.5 MPa. Moreover, the hydrogen desorption rate over the hydrogen pressure of 0.1 MPa increases noticeably with increasing dehydriding temperature. On cycling, the hydriding/dehydriding capacity increases first and then decreases, reaching a maximum value at the fourth cycle. X-ray diffraction (XRD) analyses show that the hydrogen storage process of the system is governed by the slow reaction kinetics and incomplete reaction of Na3AlH6Na3AlH6 in the hydriding/dehydriding processes.