Adsorption and diffusion of hydrogen and oxygen in FCC-Co: a first-principles study

Hydrogen and oxygen play an important role in the hydrogen embrittlement and oxidation of novel Co-based alloys with γ/γ' microstructure. In this study, the adsorption of hydrogen and oxygen atoms on the FCC-Co(111) surface and their diffusion behavior from the surface into the sub-layers and bulk have been investigated by means of first-principles calculations. It is observed that hydrogen and oxygen atoms prefer to adsorb on the fcc and hcp (threefold hollow) sites, respectively. The hydrogen atom can penetrate into the first and second sub-layers energetically, while it is not feasible for the oxygen atom as diffusion from the surface into the first sub-layer is more difficult. It is found that the calculated diffusion coefficients of hydrogen are in good agreement with the available experimental data. Finally, we briefly discuss the changes in total magnetic moment along the Oct-Tet-Oct diffusion path and the associated electronic structures. The present work is helpful to provide comprehensive guidance for the development and applications of novel Co-based alloys.