The passivation behavior of Fe in the acidic AlCl3-1-ethyl-3-methyl-imidazolium chloride（AlCl3-EMIC） ionic liquid was studied by linear sweep voltammetry and chonopotentiometry. Various approaches were used to characterize the composition and morphology of passive film formed on the Fe electrode, such as scanning electron microscopy（SEM）, Raman spectra and X-ray Photoelectron Spectroscopy（XPS）. The results showed that the critical passivation potential of Fe shifted to more negative when the molar ratio of AlCl3:EMIC changing from 2 to 1.3.A film with a light yellow color was observed on the surface of the Fe electrode after passivation. The composition of the passive film was demonstrated to be FeCl2. The passive film was composed of particulate FeCl2 with average diameter of about 500 nm. The formation of FeCl2 film was attributed to the variation of the electrolyte Lewis acidity from acidic to neutral at the interface during the dissolution process of Fe. The reason caused the variation of the electrolyte acidity was discussed.
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