Catalytic characteristics of titanium‐( IV )‐isopropoxide ( TTIP ) on de/re‐hydrogenation of wet ball‐milled MgH 2 / Mg

Magnesium hydride (MgH2) has received much attention as a solid-state hydrogen storage material worldwide due to its high hydrogen storage capacity, good reversibility, and low cost. However, its practical application has been limited due to its high thermodynamic stability and slow kinetics. In the present work, we have employed a new type of catalyst, Titanium-tetra-isopropoxide (TTIP) (Ti(OC3H7)4), to catalyze MgH2. To disperse the catalyst evenly over the MgH2, the milling operation was conducted using tetrahydrofuran (THF) as a process control agent. Here, using THF as the process control agent during the wet ball milling along with TTIP of MgH2 itself used to improve the de/re-hydrogenation behavior of MgH2. A de/re-hydrogenation investigation demonstrates that MgH2 catalyzed by TTIP has better hydrogen storage properties (onset dehydrogenation temperature 210°C) than as-cast MgH2 (onset dehydrogenation temperature ~400°C). Furthermore, a remarkable catalytic behavior of TTIP on MgH2 was observed during de-/re-hydrogenation kinetics (absorb the hydrogen ~4.6 wt% within the 1.5 minutes at a temperature of 300°C under a hydrogen pressure of 20 atm and release the hydrogen of ∼4.98 wt% within 5 minutes at ∼300°C) due to formation of intermediate compound Mg1−xTixO, and it retains nearly constant hydrogen storage capacity (from 5.25 to 5.20 wt% in rehydrogenation and from 4.95 wt % to 4.95 wt% in dehydrogenation) up to 60 cycles of de/re-hydrogenation. The estimated desorption activation energy for MgH2-TTIP using Arrhenius equation is 77.67 kJ/mol. The reason for de/re-hydrogenation kinetics improvement of MgH2-TTIP can be seen in the mechanism.