Abstract
The electrochemical behavior of passive Fe and thin, sputter-deposited films of Fe2O3 in phosphate-containing solutions was studied and compared with the behavior in berate buffer and 0.1 M NaOH. In situ X-ray absorption near edge structure (XANES) was used to simultaneously monitor changes in the samples' average valency and thickness. The reactions taking place during reduction of the passive film on iron are significantly different for all three electrolytes. In berate buffer (pH 8.4), reduction leads to a complete dissolution of the passive film. In alkaline solution, no dissolution takes place, but, instead, the passive film is converted into a lower-valent oxide/hydroxide film during reduction. In phosphate buffer (pH 8.4), there is no dissolution in a direct step to low cathodic potentials, but the resulting reduction product is metallic iron.