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TiO 2 coatings are known to protect some metals, including type 304 stainless steel, from corrosion on the basis of its reductive energy generated under UV irradiation. A TiO 2 coating is coupled with a WO 3 coating as an electron pool, in which the reductive energy can be stored. A WO 3 film on a type 304 stainless steel plate can be charged by a UV-irradiated TiO 2 coating on the same plate, in a 3 wt % NaCl aqueous solution, pH 5. The charged WO 3 coating can protect the stainless steel plate from the corrosion for a while even after the UV light is turned off. Thus, the TiO 2 coating protects the plate and charges the WO 3 coating during the day, and the charged WO 3 coating protects the plate during the night. The charge−discharge cycles are repeatable. A TiO 2 −WO 3 composite coating also has the same effects.
Tatsuma et al. (Sat,) studied this question.