DFT Study of Oxygen Reduction Reaction on Chromia and Hematite: Insights into Corrosion Inhibition

In ferrous alloys, chromia (Cr2O3) and hematite (Fe2O3) could serve as impervious passive layers to protect metals from corrosion. However, their passivating effect becomes questionable when localized defects are formed, since the oxide layers could promote oxygen reduction reactions (ORRs) as cathodes for the anodic dissolution of the exposed Fe atoms at the defect sites. Using DFT + U calculations, we investigate the ORRs on the Cr2O3 and Fe2O3 surfaces. We found that the Cr2O3 layer discourages cathodic ORRs more than the Fe2O3 layer due to a higher ORR overpotential and is thus a more effective passive layer. We also checked the overpotentials of the passive layers with Al, Fe, Cr, Mn, Mo, and Ni alloyants. We predict that Mo doping could further suppress the ORRs on both layers. In contrast, Mn is detrimental as it accelerates the oxygen reduction.