In situ creation of a catalytic multiphase and multiscale surroundings for remarkable hydrogen storage performance of MgH2
Catalyst-modified magnesium hydride (MgH2) holds the greatest promise as a solid-state hydrogen storage medium for mobile and stationary applications. However, the design and fabrication of highly active catalysts that enable MgH2 to reversibly desorb/absorb a large amount of hydrogen still remains challenging. In this work, a novel nanostructured ZrFe2 (nano-ZrFe2) measuring 30–120 nm in size was designed and fabricated as a catalyst precursor, which was readily converted into ultrafine ZrH2 and metallic Fe nanoparticles upon ball milling with MgH2 and first de-/hydrogenation, consequently delivering quite high catalytic activity for hydrogen storage in MgH2. MgH2 containing 10 wt% nano-ZrFe2 desorbed 6.2 wt% of H2 starting from approximately 193 °C, which was lowered by 35 °C with respect to the micron-ZrFe2-modified MgH2 (∼228 °C). When operated at a hydrogen pressure of 50 bars, the dehydrogenated sample absorbed ∼5.3 wt% of H2 at 200 °C within 30 minutes. The remarkably improved kinetic properties of MgH2 are mainly attributed to the ultrasmall nanoparticles and uniform, dispersive distribution of in situ formed ZrH2 and Fe. Such in situ conversion of nano-ZrFe2 not only provided a multiphase and multiscale catalytic environment that enabled high reactivity and catalytic activity but also facilitated H diffusion owing to increased interfaces, consequently promoting the dissociation and recombination of H2 molecules. These important insights in the new nanoscaled intermetallics broaden the scope of the design and synthesis of much higher active catalysts for hydrogen storage in light-metal hydrides, especially in MgH2.
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