Realizing Hydrogen De/Absorption Under Low Temperature for MgH by Doping Mn-Based Catalysts.

Magnesium hydride (MgH) has been considered as a potential material for storing hydrogen, but its practical application is still hindered by the kinetic and thermodynamic obstacles. Herein, Mn-based catalysts (MnCl and Mn) are adopted and doped into MgH to improve its hydrogen storage performance. The onset dehydrogenation temperatures of MnCl and submicron-Mn-doped MgH are reduced to 225 °C and 183 °C, while the un-doped MgH starts to release hydrogen at 315 °C. Further study reveals that 10 wt% of Mn is the better doping amount and the MgH + 10 wt% submicron-Mn composite can quickly release 6.6 wt% hydrogen in 8 min at 300 °C. For hydrogenation, the completely dehydrogenated composite starts to absorb hydrogen even at room temperature and almost 3.0 wt% H can be rehydrogenated in 30 min under 3 MPa hydrogen at 100 °C. Additionally, the activation energy of hydrogenation reaction for the modified MgH composite significantly decreases to 17.3 ± 0.4 kJ/mol, which is much lower than that of the primitive MgH. Furthermore, the submicron-Mn-doped sample presents favorable cycling stability in 20 cycles, providing a good reference for designing and constructing efficient solid-state hydrogen storage systems for future application.