A striking catalytic effect of facile synthesized ZrMn 2 nanoparticles on the de/rehydrogenation properties of MgH 2

Zr-based Laves phase alloys, especially ZrMn 2 , have been widely studied because of their good hydrogen storage properties. In this work, ZrMn 2 nanoparticles were successfully prepared by a facile wet-chemical method and then introduced to MgH 2 via ball milling to fabricate MgH 2 –ZrMn 2 composites. Remarkable improvements to the de/rehydrogenation properties were achieved with the addition of ZrMn 2 nanoparticles. The MgH 2 + 10 wt% nano-ZrMn 2 composite started to release hydrogen at 181.9 °C, which was about 160 °C lower compared with that of additive-free MgH 2 . At 300 °C, the MgH 2 + 10 wt% nano-ZrMn 2 composite desorbed 6.7 wt% hydrogen in 5 min. More importantly, the dehydrogenated MgH 2 + 10 wt% nano-ZrMn 2 sample absorbed hydrogen even at room temperature under 3 MPa hydrogen pressure, and approximately 5.3 wt% hydrogen was taken up within 10 min at 100 °C. Moreover, compared with additive-free MgH 2 , the dehydrogenation and rehydrogenation activation energies of the MgH 2 + 10 wt% nano-ZrMn 2 composites were significantly reduced to 82.2 ± 2.7 kJ mol −1 and 22.1 ± 2.7 kJ mol −1 , respectively. TEM analysis demonstrated the uniform distribution of ZrMn 2 nanoparticles in the MgH 2 matrix. Further, density functional theory calculations revealed that the presence of ZrMn 2 facilitated the breaking of the Mg–H bond, which provided a good explanation for the reduced de/rehydrogenation temperatures of the ZrMn 2 modified MgH 2 .