Sulfide and Hydrogen Bond Networks in the Electric Double Layer: Key Factors for Titanium Passivation Film Stability

Hydrogen sulfide (H₂S), carbonyl sulfide (COS), and dimethyl sulfide (DMS) are the primary sulfur compounds found in seawater, which cause pitting corrosion on the oxide passivation film of titanium, known as "the marine metals". In this study, density functional theory (DFT) was used to analyze the adsorption and surface electronic properties of these three small molecules on the anatase TiO₂(101) surface. The analysis was conducted through adsorption energy, work function, Mulliken charge population, and density of states (DOS). The hydrogen bond network structure of the electric double layer (EDL) was studied for these small-molecule systems using ab initio molecular dynamics (AIMD). The optimal adsorption configurations for H₂S, COS, and DMS on the anatase TiO₂(101) surface are 2O_b-vertical, O-down-vertical, and O_b-parallel, with adsorption energies of -1.32, -0.67, and -1.86 eV, respectively. The surface charge transfer was also investigated. Through comparative AIMD simulations of three different aqueous solutions on the TiO₂(101) surface, we observed that COS exerts a more pronounced influence on the electrical double layer within 3.00 Å of the TiO₂(101) surface. Specifically, the hydrogen atoms of water tend to aggregate toward the O_b atoms, forming hydrogen bonds, which significantly impacts the corrosion resistance of the TiO₂ surface.