Hydrogen peroxide oxidation on passive iron in alkaline solutions

Abstract

The kinetics of hydrogen peroxide oxidation were studied on passive iron in alkaline solutions of pH ranging from 9.8 to 13.8, using the rotating disk electrode. Measurements were taken using the linear sweep technique. The kinetic parameters of H2O2 oxidation were determined: the Tafel slope is 110 mV dec-1 and the reaction order with respect to H2O2 is 0.5 and with respect to the OH- ion 0.7. It is assumed that the rate determining step is the transfer of the first electron to the HO-2 ion adsorbed under Temkin conditions. The pH dependence of the reaction rate is attributed to the pH dependent properties of the passive iron surface. There are no indications for the semiconducting behaviour of the passive film. The rate of H2O2 chemical decomposition was estimated. It was found that the passive film on iron was a poor catalyst for H2O2 chemical decomposition.