Multivalent transition metal oxyfluorides as efficient catalysts for improving hydrogen cycling kinetics of MgH2

Magnesium hydride is a promising solid-state hydrogen storage material with a hydrogen capacity of 7.6 wt%. However, its practical applications are limited by high thermodynamic stability, sluggish desorption kinetics and poor cycling stability. To enhance the hydrogen desorption kinetics and cycling stability of MgH 2 , nanosized TiOF 2 and NbO 2 F are synthesized as catalytic additives in this work. After the preparation by ball milling and activation by de/hydrogenation cycling of MgH 2 –10 wt% TiOF 2 and MgH 2 –10 wt% NbO 2 F composites, the highly dispersed magnesium fluoride, magnesium-transition metal oxides and transition metal hydrides as well as multivalent transition metal species can be in-situ formed throughout the samples. Benefiting from the synergistic effect of these secondary phases, the two samples exhibit fast dehydrogenation kinetics with activation energies of 76.2 and 74.4 kJ mol −1 , respectively. It is noteworthy that the microstructure configurations can be preserved well after 50 cycles. Consequently, the dehydrogenation activation energies of the cycled samples only increase to 80.5 and 78.7 kJ mol −1 , respectively, showing good cycling stability. These results demonstrate that multivalent transition metal oxyfluorides can be used as efficient additives to improve hydrogen storage properties of MgH 2 .