Coverage and Strain Effects on Adsorption and Diffusion of Hydrogen over Al(111) from First Principles

The diffusion of hydrogen in aluminum is thought to be a critical process in the embrittlement of aluminum. Experimentally determined diffusivities reported in the literature, however, provide little guidance into understanding hydrogen diffusion in aluminum as measurements taken at 20 C vary by over 17 orders of magnitude. Herein, we use ab initio methods to elucidate the elementary diffusion and adsorption processes for hydrogen in aluminum and to help understand the disparate values reported in the literature. We carried out plane wave gradient-corrected ab inito density functional theory calculations to determine the adsorption, lateral interaction, and diffusion energies for hydrogen on and in ideal Al(111). The calculations were performed over a coverage range of [ ] 9 ,1 Θ∈ and a strain range of [ ] 0%,5% ε ∈ in order to establish the effects of coverage and strain. The results showed that the hydrogen binding energy is between –1.9 and –2.0 eV. The barrier for hydrogen diffusion and uptake at low coverage and strain were found to be 0.11 and 0.54 eV, respectively. Investigation into the rate-limiting paths that control diffusion indicate that hydrogen can diffuse ballistically over this ideal closed packed aluminum surface.