The influences of the water content on the electrochemical properties of Type 304 stainless steel were studied through cyclic voltammetry and chronoamperometry in the ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI). The electrochemical behavior of stainless steel was explained by the reactivity of water in the ionic liquid with the main constituent elements of the stainless steel, such as Fe, Cr, and Ni. A protective passive film formed on the surface of stainless steel in EMI-TFSI with the water content controlled in the range of 5.5 ppm to 5000 ppm. For a water content less than 5.5 ppm, however, the stainless steel was not passivated and, therefore, was corroded by the dissolution. The amount of eluted metal ions from Type 304 stainless steel were much less than Fe and Ni. Furthermore, the dissolution process did not change in a wide temperature range from room temperature to 120°C.

SUS304 and SUS430LX stainless steels were subjected to cyclic voltammetry (CV) in EMI-TFSI ionic liquid containing water of 5.5, 30 and 5000 ppm at room temperature. Structural changes of passive film during CV was characterized by AES and TEM/EELS. Passive films after CV were mainly composed of mainly Cr and Fe oxides similar to that formed in aqueous solutions. The thickness and Cr cation fraction of passive film increased with increasing CV cycles. Furthermore, much Cr concentrated and thinner passive films were formed with less water content in EMI-TFSI. It is concluded that SUS304 and SUS430LX stainless steel are corrosion resistant in EMI-TFSI ionic liquid with small amount of water.