Improvement of hydrogen storage properties in MgH2 catalysed by K2NbF7

Abstract

The catalytic effects of K2NbF7 on the hydrogen storage properties of MgH2 have been studied for the first time. MgH2 + 5 wt% K2NbF7 has reduced the onset dehydrogenation temperature to 255 °C, which is 75 °C lower than the as-milled MgH2. For the rehydrogenation kinetic, at 150 °C, MgH2 + 5 wt% K2NbF7 absorbs 4.7 wt% of hydrogen in 30 min whereas the as-milled MgH2 only absorbs 0.7 wt% of hydrogen under similar condition. For the dehydrogenation kinetic, at 320 °C, the MgH2 + 5 wt% K2NbF7 is able to release 5.2 wt% of hydrogen in 5.6 min as compared to 0.3 wt% by the as-milled MgH2 under similar condition. Comparatively, the Ea value of MgH2 + 5 wt% K2NbF7 is 96.3 kJ/mol, which is 39 kJ/mol lower compared to the as-milled MgH2. The MgF2, the KH and the Nb that are found after the heating process are believed to be the active species that have improved the system properties. It is concluded that the K2NbF7 is a good catalyst to improve the hydrogen storage properties of MgH2.