Graphene-Coated ZnO and SiO₂ as Supports for CoO Nanoparticles with Enhanced Reducibility

The insertion of a graphene layer between cobalt and a substrate modifies the morphology and the oxidation/reduction properties of supported cobalt particles. Co forms a relatively flat structure on ZnO and SiO₂ , whereas individual Co nanoparticles are formed after graphene coating of these substrates. The graphene layer moderates the formation of cobalt oxide in 5×10^-7  mbar O₂ and promotes the reduction of oxidized Co in H₂ at lower temperature. Angle-resolved XPS measurements indicate that this is mainly a consequence of the restricted interaction of cobalt with the oxide supports. After the low-pressure redox treatments, the graphene layer maintains a relatively high quality with a small number of defect sites.