Linear dependence of potential drop at the passive film/solution interface on film-formation potential and pH: Combining first-principles calculations with experiments

Herein, we develop a model presenting the linear dependence of potential drop at passive film/solution interface (φf/s) on both potential and pH. By analyzing surface charge and performing first-principles calculations, we provide the insights into the effect of potential and pH on the φf/s, and into the linear relation between φf/s with pH beyond the Nernst relation that is attributed to the role of point defects in point of zero charge of passive film on iron. Two methods are suggested to determine values of α and β. The study of passivity of iron in borate buffer solutions validates our model.