Molecular insights into the effect of adsorption and reaction of H2O-O2-Cl- on initial electrochemical corrosion of steel

A deeper understanding of the effect of chloride on the process of iron initial corrosion could reveal the detailed mechanism of the Cl^--induced acceleration corrosion of steel. In light of the difficulty to unravel the intricacies of H₂O-O₂-Cl^- interactions in experiments, this study conducted the molecular study on the effect of H₂O, O₂ and Cl^- coadsorption and interactions on the electrochemical corrosion process of Fe (100) surface by DFT method, and the electron-correlation functional is GGA-PW91. It is discovered that the adsorption of H₂O, O₂ and Cl^- all promote the electrochemical corrosion of iron. The electrochemical corrosion rate of iron surface rises as the Cl^-/H₂O concentration ratio increasing, while decrease with the Cl^-/O₂ concentration ratio increasing. The transition state search found that the presence of Cl^- assists the dissociation of H₂O on the iron surface, while the interaction between Cl^- and O₂ could be ignored. Moreover, the successive reaction of Cl^-, H₂O and O₂ with iron surface were further investigated. When the Cl^- reacts with H₂O ahead of O₂, the Cl^- promotes the iron oxidation via promoting the dissociation of H₂O. While O₂ and Cl^- firstly coadsorb on iron surface, Cl^- accelerates iron oxidation by exacerbating the iron surface losing electrons. These findings could facilitate the development of anti-corrosion techniques for steel in chloride environment.