Non-stationarity in electrochemical impedance measurement of Mg-based materials in aqueous media

For most bare Mg-based materials in aqueous media, an inductive behavior can be detected at the low frequencies electrochemical impedance spectroscopy (LF-EIS) measurement, which potentially can be associated with the non-stationarity of the system. The non-stationarity in EIS measurement leads to inaccurate acquisition of experimental data and, thus, misunderstanding of the electrochemical behavior of tested samples. To investigate the non-stationarity of EIS measurements on Mg-based materials in aqueous media, conventional EIS measurements are performed on pure Mg and several representative Mg alloys (AZ31, AZ91, AM50) in NaCl and Na2SO4 solutions. The results indicate that the impedance spectra of Mg-based materials in aqueous media is influenced by the internal non-stationarity of the Mg-electrolyte system and the external non-stationarity induced by EIS measurement. Multisine odd random phase EIS (ORP-EIS) measurements were performed to visualize the non-stationarity and non-linearity of the system. Moreover, the comparison of conventional and ORP-EIS results exhibits the difference between pseudo and real inductive behavior for the AZ31-NaCl system. Accordingly, the origin of the inductive behavior of Mg-based materials is discussed.