The limitations of graphene as an effective corrosion-inhibiting coating on metal
surfaces, here exemplified by the hex-reconstructed Pt(100) surface, are probed by scanning tunneling
microscopy measurements and density functional theory calculations. While exposure of small molecules
directly onto the Pt(100) surface will lift the reconstruction, a single graphene layer is observed to act as
an effective coating, protecting the reactive surface from O2 exposure and thus preserving the
reconstruction underneath the graphene layer in O2 pressures as high as 104 mbar. A similar protective
effect against CO is observed at CO pressures below 106 mbar. However, at higher pressures CO is
observed to intercalate under the graphene coating layer, thus lifting the reconstruction. The limitations
of the coating effect are further tested by exposure to hot atomic hydrogen. While the coating can
withstand these extreme conditions for a limited amount of time, after substantial exposure, the Pt(100)
reconstruction is lifted. Annealing experiments and density functional theory calculations demonstrate
that the basal plane of the graphene stays intact and point to a graphene-mediated mechanism for the H-induced lifting of the reconstruction.