We investigate and discuss the interaction of H2 with graphene based on density functional (DFT) theory. We calculate the potential energy surfaces for the dissociative adsorption of H2 on highly symmetric sites on graphene. Our calculation results show that reconstructions of the carbon atoms play an important role in the H2 -graphene interactions. Activation barrier for H2 dissociation on an unrelaxed graphene is considerably high, ∼4.3 eV for a T–H–T geometry and ∼4.7 eV for a T–B–T geometry. The T–H–T(T–B–T) geometry means that the center of mass position of H2 is at the hollow(bridge) site, and the two H atoms are directed towards the top sites on the graphene. On the other hand, when the carbon atoms are allowed to relax, the activation barrier decreases, and becoming 3.3 eV for the T–H–T geometry and 3.9 eV for the T–B–T geometry. In this case, the two carbon atoms near the hydrogen atoms move 0.33 Å towards the gas phase for the T–H–T geometry and 0.26 Å for the T–B–T geometry.

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We calculate the adiabatic potential energy for hydrogen atom motion on a Pd͑111͒ surface and in a subsurface within the framework of the density functional theory in order to understand the diffusion mechanism of a hydrogen atom from the Pd͑111͒ surface to the subsurface. According to the calculated adiabatic potential energy surface for the hydrogen atom motion up to the third atom layer, an effective diffusion path of the hydrogen atom into the Pd bulk starts from the fcc hollow site on the Pd͑111͒ surface. Moreover, the diffusion path passes through the octahedral site between the first and the second Pd atom layers, the tetrahedral site beneath a Pd atom of the first layer or above the Pd atom of the third layer, and the octahedral site between the second and third layer.

We report results of our experimental and theoretical studies on the oxidation of Cu-Au alloy surfaces, viz., Cu3Au(111), CuAu(111), and Au3Cu(111), using hyperthermal O2 molecular beam (HOMB). We observed strong Au segregation to the top layer of the corresponding clean (111) surfaces. This forms a protective layer that hinders further oxidation into the bulk. The higher the concentration of Au in the protective layer formed, the higher the protective efficacy. As a result, of the three Cu-Au surfaces studied, Au3Cu(111) is the most stable against dissociative adsorption of O2, even with HOMB. We also found that this protective property breaks down for oxidations occurring at temperatures above 300 K.