A striking catalytic effect of facile synthesized ZrMn2 nanoparticles on the de/rehydrogenation properties of MgH2

Abstract

Zr-based Laves phase alloys, especially ZrMn₂, have been widely studied because of their good hydrogen storage properties. In this work, ZrMn₂ nanoparticles were successfully prepared by a facile wet-chemical method and then introduced to MgH₂via ball milling to fabricate MgH₂–ZrMn₂ composites. Remarkable improvements to the de/rehydrogenation properties were achieved with the addition of ZrMn₂ nanoparticles. The MgH₂ + 10 wt% nano-ZrMn₂ composite started to release hydrogen at 181.9 °C, which was about 160 °C lower compared with that of additive-free MgH₂. At 300 °C, the MgH₂+ 10 wt% nano-ZrMn₂ composite desorbed 6.7 wt% hydrogen in 5 min. More importantly, the dehydrogenated MgH₂ + 10 wt% nano-ZrMn₂ 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 MgH₂, the dehydrogenation and rehydrogenation activation energies of the MgH₂ + 10 wt% nano-ZrMn₂ 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 ZrMn₂ nanoparticles in the MgH₂ matrix. Further, density functional theory calculations revealed that the presence of ZrMn₂ facilitated the breaking of the Mg–H bond, which provided a good explanation for the reduced de/rehydrogenation temperatures of the ZrMn₂ modified MgH₂.