The design of original protections of metals to hydrogen embrittlement required a precise knowledge of solubility and diffusion of the solute in the surface and in the subsurface layers. This special zone in the material acts as the door for hydrogen and the surface reactivity, as well as the short-scale diffusion in the subsurface layers, may have strong implications in the hydrogen embrittlement mechanisms.
Here, we have conducted first principles calculations within density functional theory (DFT) on the adsorption, absorption and diffusion of H in the (100) surface and subsurface layers of Ni. The calculations are performed up to the melting point where the adsorption, absorption and migration Gibbs free energies are expressed as a sum of vibration and electronic contributions from the computation of the phonon dispersion curve and the electronic density of states. Three sites for adsorption including at the top of a Ni atom, at the bridge position between 2 Ni atoms and in the pseudo-octahedral site but also different H-coverage are investigated. The H concentrations in the absorption sites are calculated down to the bulk material. The H diffusion coefficients are determined both parallel and perpendicular to the surface plane. Our results show that the subsurface layers do not favour the hydrogen incorporation and act as accelerating paths for the diffusion. The method exposed in the presentation will be extended to the (110) and (111) surfaces of Ni in the future.