Functionalization of graphene grown on metal substrate with atomic oxygen: enolate vs epoxide

Graphene functionalization is of great importance in applying graphene as a component in functional devices or in activating it for use as a catalyst. Here we reveal that atomic oxidation of epitaxial graphene grown on a metal substrate results in the formation of enolate, i.e., adsorption of atomic oxygen at the on-top position, on the basal plane of a graphene, using periodic density functional theory calculations. This is striking because the enolate corresponds to the transition state between the epoxides on free-standing graphene and on graphite. Improved interfacial interaction between graphene and the metal substrate during atomic oxidation makes the graphene enolate a local minimum and further highly stabilizes it over the graphene epoxide. Our results provide not only a novel perspective for a chemical route to functionalizing graphene but also a new opportunity to utilize graphene enolate for graphene-based applications.