Visualizing dynamic evolution of electrode/electrolyte interface via model-free analysis of in-situ spectroscopic ellipsometry

Spectroscopic ellipsometry is a promising technique for realizing in-situ study of electrode/electrolyte interface (EEI) owing to its high-sensitive and non-destructive advantages. However, difficulties in modelling complex systems and analysing massive data of in-situ tests hinder its widespread applications. Herein, a model-free method was established and a featured parameter named interfacial evolution rate (IER) was proposed to qualitatively and quantitatively probe the dynamic evolution rate of EEI. The in-situ electrochemistry-spectroscopic ellipsometry measurement of pure magnesium corrosion in 5 wt.% NaCl solution before and after adding Na2SiO3·9H2O inhibitor (0.001 mol L−1) was conducted to verify the utility of the established method. Without the inhibitor, IER exponentially decreases from 12 to 3 and lasts for about 60 min, indicating the gradual stabilization of the interface. The subsequent increase of IER suggests the accelerated dynamic evolution of EEI. In the presence of the inhibitor, IER decreases from 0.5 to 0.3 and remains stable for 230 min, corresponding to the significant corrosion inhibition of sodium silicate. Ex-situ SEM, EDS, Raman and XPS characterizations of the corrosion products were also performed to support the analysis. The model-free analysis method of spectroscopic ellipsometry established in this work shows potential applications in the in-situ investigations of various complex systems.