Coverage dependent water dissociative adsorption on Fe(110) from DFT computation

Abstract

Using density functional theory calculations and ab initio atomistic thermodynamics, H₂O adsorption and dissociation on the Fe(110) p(4 × 4) surface at different coverages have been computed. At the lowest coverage, the adsorbed H₂O, OH, O and H species can migrate easily on the surface. For (H₂O)_n adsorption, H₂O molecules donating H atoms for H-bonding adsorb more strongly than those accepting H atoms for H-bonding. Monomeric H₂O dissociation is favored both thermodynamically and kinetically. On nO pre-covered Fe(110) surfaces (n = 1–8), H₂O dissociation is accessible for nO + H₂O (n = 1–7) both kinetically and thermodynamically, while H₂O desorption instead of dissociation occurs at n = 8. With the increased number of surface O atoms, H₂ dissociative adsorption energies vary in a narrow range for n = 1–4 and decrease for n = 5–7, while at n = 8, the surface does not adsorb H₂. At low OH coverage (n = 2, 4), OH groups are perpendicularly adsorbed without H-bonding, while for n ≥ 6, adsorbed OH groups are linearly arranged and stabilized by H-bonding. The maximal OH coverage (n = 12) is 0.75 ML and the reasonable O coverage (n = 7) is 0.44 ML, in line with the experiment. The calculated desorption temperatures of H₂O and H₂ agree well with the available experimental data. These results provide fundamental insights into water-involved reactions catalyzed by iron and interaction mechanisms of water interaction with metal surfaces.