Extraction of Kinetic Parameters in the Point Defect Model through Coupled Transient Current Response and Electrochemical Impedance Spectroscopy

Understanding the growth kinetics of passive films is crucial for controlling corrosion resistance. However, the mechanistic origin of the commonly observed current transients remains unclear, and uniquely determining the interfacial kinetic parameters remains challenging. In this presentation, the transient growth behavior of passive films on Fe, Ti, Ni, and Cu was investigated using potentiostatic current density-time (I-t) analysis combined with Mott–Schottky measurements. Within the framework of the point defect model (PDM), a systematic methodology was established to interpret I-t curves. A two-stage double-logarithmic relationship in log I–log t plots is attributed to film growth governed by oxygen vacancies coupled with metal cation interstitials or vacancies, whereas a single-stage behavior indicates control by a single defect type. The slope of the log I–log t plot is determined by the ratio of interfacial transfer coefficients, with a more negative slope corresponding to the formation of a denser passive film with fewer defects. Importantly, integrating I-t analysis with electrochemical impedance spectroscopy (EIS) enables quantitative determination of the kinetic parameters of interfacial defect reactions in the PDM. While I-t transients constrain transport and reaction kinetics during early-stage growth, EIS provides complementary information on interfacial reaction resistances and capacitances under steady-state conditions. Their combined application offers a more reliable and internally consistent strategy for extracting transfer coefficients and rate constants, thereby strengthening parameter identification within the PDM framework.