  Light-driven plasmonic enhancement of chemical reactions on metal catalysts
is a promising strategy to achieve highly selective and efficient chemical
transformations. The study of plasmonic catalyst materials has traditionally
focused on late transition metals such as Au, Ag, and Cu. In recent years,
there has been increasing interest in the plasmonic properties of a set of
earth-abundant elements such as Mg, which exhibit interesting hydrogenation
chemistry with potential applications in hydrogen storage. This work explores
the optical, electronic, and catalytic properties of a set of metallic Mg
nanoclusters with up to 2057 atoms using time-dependent density functional
tight-binding and density functional theory calculations. Our results show that
Mg nanoclusters are able to produce highly energetic hot electrons with
energies of up to 4 eV. By electronic structure analysis, we find that these
hot electrons energetically align with electronic states of physisorbed
molecular hydrogen, occupation of which by hot electrons can promote the
hydrogen dissociation reaction. We also find that the reverse reaction,
hydrogen evolution, can potentially be promoted by hot electrons, but following
a different mechanism. Thus, from a theoretical perspective, Mg nanoclusters
display very promising behaviour for their use in light promoted storage and
release of hydrogen.
