Sodium fluotitanate with the formation of multicomponent catalytic species for superior hydrogen storage of magnesium hydride

Abstract

Magnesium hydride (MgH2) has attracted more research interest as an excellent solid hydrogen storage material. Still, its stable thermodynamics and sluggish kinetics are the main obstacles to the widespread application, which can be solved by the exploration of an efficient catalyst to improve its hydrogen storage performance. In this study, sodium fluotitanate (Na2TiF6, NTF) as an additive was introduced into MgH2 through ball milling to enhance its hydrogen storage performance because there is a potential formation of fluoride, titanium-containing substance and sodium-bearing species that are beneficial for performance improvement. Unsurprisingly, the mechanism analysis shows that the in-situ generated TiH2, MgF2, NaMgH3, and TiF4 catalytically active species can realize the dual regulation of kinetic and thermodynamic properties, which together coordinate the enhancement of the hydrogen storage properties of MgH2. The starting hydrogen release temperature of MgH2-NTF-10 is significantly decreased to 226 °C, about 183 and 33 °C lower than pristine MgH2 and as-milled MgH2, respectively. About 6.1 wt% of hydrogen can be released at 300 °C in only 30 min with a much lower activation energy of 143.08 kJ/mol. Moreover, the reversible hydrogen storage performance is well displayed for MgH2-NTF-10 after ten cycles of hydrogen de/absorption, with 95% hydrogen storage capacity retention. Our results show that the synergistic functions of multiphase active components from the three-in-one additive of NTF may advance MgH2 further to practical applications.