Oxygen reduction on iron. Part VII. Temperature dependence of oxygen reduction on passivated iron in alkaline solutions
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The temperature dependence of the kinetics of O2 reduction was studied on passivated Fe in NaOH solutions having a concentration ranging from 0.010 to 1.0 mol dm-3 and in the temperature range from 2 to 42 °C. The apparent enthalpy of activation was determined and was found to be pH dependent. The Tafel slpe increased with temperature in the range -69 to -92 mV dec-1. The enthalpic and entropic components of the transfer coefficient were calculated and these values were also pH dependent. As a consequence of the pH dependence of the apparent enthalpy of activation and of the transfer coefficient components, the reaction order with respect to OH- could not be determined precisely. Its value depends on the potential and temperature and was estimated to be about -0.8. Such complex temperature and pH behavior of O2 reduction on passive Fe was attributed to the pH, temperature and potential dependence of the passive film properties.
Keywords:Alkaline solutions / Iron / Oxygen / Reduction
Source:Journal of Electroanalytical Chemistry, 1995, 399, 1-2, 127-133
- Elsevier Science Sa, Lausanne