Abstract
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.
Highlights
Clean and sustainable energy is attracting tremendous attention worldwide because of the continuous shortage of fossil fuels and the worsening of environmental pollution
Compared with the liquid and gaseous hydrogen, hydrogen stored in solid-state materials has the advantage of high hydrogen storage density, and keeps safety during application [8,9,10]
Magnesium hydride (MgH2) with large mass hydrogen storage capacity (7.76 wt%), natural abundance, and excellent reversibility, ignites hope for meeting the demands of practical application of high-capacity hydrogen storage [11,12,13]
Summary
Clean and sustainable energy is attracting tremendous attention worldwide because of the continuous shortage of fossil fuels and the worsening of environmental pollution. Transition metal halides were easy to be obtained and doped to MgH2 to improve its hydrogen storage properties [36,37,38,39,40,41]. According to the above references, it can be concluded that doping transition metal halides into MgH2 could greatly enhance the de/hydrogenation properties. As far as we know, studies about Mn-based catalysts have rarely been researched, it is urgent and interesting to explore the catalytic effect of MnCl2 for the reversible hydrogen storage performance of MgH2. The catalytic effect of MnCl2 was investigated and based on the microstructure evidence, submicron-Mn was successfully synthesized via a simple wet chemical method and doped directly to MgH2 to further enhance the hydrogen storage properties of MgH2. Its catalytic mechanism was explored and discussed in detail
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