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

•The role of Cl- in the steel corrosion under the H2O-O2 interaction was revealed at atomic scale.•The adsorption of H2O, O2 and Cl- all promote the electrochemical corrosion of iron.•The presence of Cl- assists the dissociation of H2O molecule on iron surface.•The iron corrosion induced by H2O is significantly affected by Cl- concentration.•The presence of Cl- has little effect on the iron corrosion induced by O2. 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. [Display omitted]