Increased interactions at the graphene-metal interface are here demonstrated to yield an effective prevention of intercalation of foreign species below the graphene cover. Hereby, an engineering pathway for increasing the usability of graphene as a metal coating is demonstrated. Graphene on Ir(111) (Gr/Ir(111)) is used as a model system, as it has previously been well-established that an increased interaction and formation of chemical bonds at the graphene-Ir interface can be induced by hydrogen functionalization of the graphene from its top side. With X-ray photoelectron spectroscopy, it is shown that hydrogen-induced increased interactions at the Gr/Ir(111) interface effectively prevents intercalation of CO in the millibar range. The scheme leads to protection against at least 10 times higher pressure and 70 times higher fluences of CO, compared to the protection offered by pristine Gr/Ir(111).

Hydrogen functionalization of graphene by exposure to vibrationally excited H₂ molecules is investigated by combined scanning tunneling microscopy, high-resolution electron energy loss spectroscopy, X-ray photoelectron spectroscopy measurements, and density functional theory calculations. The measurements reveal that vibrationally excited H₂ molecules dissociatively adsorb on graphene on Ir(111) resulting in nanopatterned hydrogen functionalization structures. Calculations demonstrate that the presence of the Ir surface below the graphene lowers the H₂ dissociative adsorption barrier and allows for the adsorption reaction at energies well below the dissociation threshold of the H-H bond. The first reacting H₂ molecule must contain considerable vibrational energy to overcome the dissociative adsorption barrier. However, this initial adsorption further activates the surface resulting in reduced barriers for dissociative adsorption of subsequent H₂ molecules. This enables functionalization by H₂ molecules with lower vibrational energy, yielding an avalanche effect for the hydrogenation reaction. These results provide an example of a catalytically active graphene-coated surface and additionally set the stage for a re-interpretation of previous experimental work involving elevated H₂ background gas pressures in the presence of hot filaments.