  Improving reactivity on an insulating surface is crucial due to their
important applications in surface catalytic reactions. In this work, we carried
out first-principles calculations to investigate the adsorption of O2 on a
single-layer MgO(100) film deposited on metal substrate. The adsorption
configurations, reaction pathways, molecular dynamics simulations, and
electronic properties are reported. We reveal that O2 can completely dissociate
on the surface, which is in sharp contrast to that on MgO(100) films thicker
than one monolayer. The dissociated O2 tends to penetrate into the interfacial
region, behaving like a switch to trigger subsequent chemical reactions. As an
example, the interplay between water and the interfacial oxygen results in the
formation of hydroxyl radicals. This study paves an avenue to accomplish the
desired surface catalytic reactions, especially those involving oxygen.
