Towards quantum corrosion chemistry: screening perfect Cr, Ni sites and stoichiometry on top of an Fe(110) surface using DFT

For decades, corrosion has been classified into many categories according to the microstructural morphology of the chemical reaction products. Until recently, the development of quantum chemistry has simplified the fundamental corrosion mechanism into only two processes: electrochemical dissolution and hydrogen evolution reaction (HER). Although Cr and Ni elements have been found to segregate towards the surface of stainless steel to form a protective layer and prevent Fe dissolution, the understanding of the exact chemistry on top of the Fe surface has not been reported in previous studies. In this study, we have identified suitable doping sites for simultaneous doping of several Cr and Ni atoms, and quantified the effects of different alloy compositions (Fe(12)Cr(3)Ni(1), Fe(11)Cr(4)Ni(1), Fe(11)Cr(3)Ni(2), Fe(10)Cr(4)Ni(2), Fe(10)Cr(3)Ni(3)) on the stability from two aspects: electron transfer and atomic dissolution. It was found that the doping atoms are more likely to be dispersed rather than aggregated in solid solution. When Cr atoms are symmetrically distributed and Ni atoms are located in the center, it is the site arrangement with the highest work function and stability. Fe(10)Cr(4)Ni(2) has been found to possess a higher electron binding capacity and thus higher electrode potentials. This is determined by the change of dipole caused by both electronegativity difference between atoms and polarization between the doped layer and the substrate layer. By calculating the vacancy formation energy, it is shown that Fe(11)Cr(4)Ni(2) is the perfect chemistry on top of the Fe(110) surface due to its high ability of preventing atomic dissolution.