Hydrogen is one of the most promising “green” fuels simply because the ultimate product of its combustion is water vapor. The challenge is, however, how to store hydrogen at relatively high gravimetric/volumetric densities and with good uptake/release rates. Current commercially available hydrogen fuel cell vehicles store compressed hydrogen in cylindrical tanks, which have low volumetric capacity and raise safety concerns particularly related to the high pressures involved. Solid-state storage, based on metal hydrides, provides an alternative means to store hydrogen with sufficient storage density for efficient vehicular applications. The simplest form of metal hydride is probably MgH<sub>2</sub>. Although magnesium tends to bind too strongly with hydrogen, the binding enthalpy can be reduced when considering nanostructures. However, the oxidative instability of these nanomaterials should be well controlled in order to maintain long-term cyclability. Recent study shows that embedding magnesium nanoparticles into reduced graphene oxide can effectively protect them from oxygen and moisture. Although no bulk-like crystalline MgO layer has been clearly identified in this graphene-encapsulated/Mg nanocomposite, we propose that an atomically thin layer of honeycomb suboxide exists, based on first-principles interpretation of Mg K-edge X-ray absorption spectra. Density functional theory calculations reveal that in contrast to conventional expectations for thick oxides this interfacial oxidation layer permits di-hydrogen dissociation to the same degree as pristine Mg metal with the added benefit of enhancing the binding between reduced graphene oxide and the Mg nanoparticle, contributing to improved mechanical and chemical stability of the functioning nanocomposite.

Atomically thin interfacial suboxide key to hydrogen storage performance enhancements of magnesium nanoparticles encapsulated in reduced graphene oxide

255th National Meeting (2018)

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