RESUMO
As an ideal material for solid-state hydrogen storage, magnesium hydride (MgH2) has attracted enormous attention due to its cost-effectiveness, abundant resources, and outstanding reversibility. However, the high thermodynamics and poor kinetics of MgH2 still hinder its practical application. In this work, a simple stirring-hydrothermal method was used to successfully prepare bimetallic Mn3O4/ZrO2 nanoparticles, which were subsequently doped into MgH2 by mechanical ball milling to improve its hydrogen sorption performance. The MgH2 + 10 wt% Mn3O4/ZrO2 composite began discharging hydrogen at 219 °C, which was 111 °C lower compared to the as-synthesized MgH2. At 250 °C, the MgH2 + 10 wt% Mn3O4/ZrO2 composite released 6.4 wt% hydrogen within 10 min, whereas the as-synthesized MgH2 reluctantly released 1.4 wt% hydrogen even at 335 °C. Moreover, the dehydrogenated MgH2 + 10 wt% Mn3O4/ZrO2 sample started to charge hydrogen at room temperature. 6.0 wt% hydrogen was absorbed when heated to 250 °C under 3 MPa H2 pressure, and 4.1 wt% hydrogen was taken up within 30 min at 100 °C at the same hydrogen pressure. In addition, compared with the as-synthesized MgH2, the de/rehydrogenation activation energy values of the MgH2 + 10 wt% Mn3O4/ZrO2 composite were decreased to 64.52 ± 13.14 kJ mol-1 and 16.79 ± 4.57 kJ mol-1, respectively, which incredibly contributed to the enhanced hydrogen de/absorption properties of MgH2.
RESUMO
Magnesium hydride (MgH2) 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 (MnCl2 and Mn) are adopted and doped into MgH2 to improve its hydrogen storage performance. The onset dehydrogenation temperatures of MnCl2 and submicron-Mn-doped MgH2 are reduced to 225 °C and 183 °C, while the un-doped MgH2 starts to release hydrogen at 315 °C. Further study reveals that 10 wt% of Mn is the better doping amount and the MgH2 + 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% H2 can be rehydrogenated in 30 min under 3 MPa hydrogen at 100 °C. Additionally, the activation energy of hydrogenation reaction for the modified MgH2 composite significantly decreases to 17.3 ± 0.4 kJ/mol, which is much lower than that of the primitive MgH2. 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.
