In situ formed MgTi2O4 from MgO improving the cycling stability of MgH2

Abstract

Magnesium hydride (MgH2) is a potential candidate for hydrogen storage due to its high gravimetric and volumetric hydrogen capacities. However, high operating temperature and reversible H2 capacity attenuation inhibit its commercial application. To overcome these issues, we synthesized an N ion-doped Na2TiO3 (denoted as N-NaTiO) catalyst by reducing TiO2 with NaNH2. Experimental results show that the addition of 5 wt% N-NaTiO can lower the dehydrogenation peak temperature of MgH2 from 328 to 239 °C, and 6.0 wt% H2 is quickly released in ca. 4 min at 300 °C. In particular, the modified MgH2 exhibits a high reversible hydrogen capacity of 6.7 wt% which is equal to a retention of 94.4% after 250 cycles. Reaction mechanism investigations reveal that hydrogen insertion and removal during the ab/desorption processes are consistent with the reversible change of titanium valence states in the catalyst. In addition, it is observed that there is an irreversible evolution of MgO to MgTi2O4 at the interface between the catalyst and MgH2 during the cycling process, which is linked to the improvement of the ab/desorption kinetics and cycle stability.