A DFT study on hydrogen diffusion across zinc surfaces at low coverage

Abstract

Abstract The mechanism governing hydrogen diffusion on Zn surfaces plays a crucial role in the hydrogen evolution reaction (HER). This reaction is vital for various technological applications, particularly its influence on the cycling stability of aqueous Zn-ion batteries. However, the fundamental relationship between hydrogen diffusion, Zn surface properties, and HER remains unclear. In this study, we investigate the dynamics of hydrogen on Zn surfaces using density functional theory and ab initio molecular dynamics. Molecular dynamics data allow us to estimate the vibrational density of states of adsorbed hydrogen and to calculate the diffusion coefficients. Vibrational data indicate that the vibrational motion parallel to the surface of the hydrogen atom has a similar frequency to that of the surface phonons, suggesting the role of vibrations in the diffusion process; moreover, we calculate the diffusion coefficient on top of a frozen surface and get values that are several orders of magnitude lower than those obtained in the presence of surface phonons, i.e. $$\approx 10^{-8}$$ $${\text{m}}^2/{\text{s}}$$ .