Photoelectrochemical and corrosion properties of Fe2O3-TiO2 artificial passivation films

Fe2O3-TiO2 artificial passivation films were formed on Pt substrates by low-pressure metallorganic chemical vapor deposition, and their corrosion resistance and photoelectrochemical properties were examined in acidic, neutral, and alkaline solutions. The corrosion resistance was examined by an anodic polarization test and the photocurrent response by a photoelectrochemical polarization test. The quantum yield maximum of the films depends on the cationic fraction of Ti4+ of the films, X-Ti. It decreased in the range X-Ti = 0.0-070, then increased in the range X-Ti = 0.70-0.95, and finally decreased in the range X-Ti = 0.95-1.0 with increasing X-Ti value. The films in the ranges of X-Ti = 0.0-0.70 and 0.95-1.0 had crystalline structure and the films in the range 0.70-0.95 had amorphous structure. Therefore, the increase in the quantum yield maximum in the range X-Ti = 0.70-0.95 was attributed to the amorphous structure. Such a change in the quantum yield maximum was independent of solution pH. The corrosion resistance of the films increased with increasing X-Ti value of the film in a 5.0 M HCl solution. Therefore, the films with X-Ti = 0.70-0.95 can be concluded to have high quantum yield and high corrosion resistance. (C) 1999 The Electrochemical Society. S0013-4651(97)09-028-9. All rights reserved.