In situ creation of a catalytic multiphase and multiscale surroundings for remarkable hydrogen storage performance of MgH2

Abstract

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.