Oxygen reduction on iron-IV. The reduction of hydrogen peroxide as the intermediate in oxygen reduction reaction in alkaline solutions

Abstract

The kinetics of hydrogen peroxide reduction were studied on iron in borate buffered and unbuffered solutions of pH ranging from 8.6 to 13.8, with and without the presence of chloride ions. A rotating disk electrode was employed. Measurements were taken using the linear sweep technique and the potential step steady-state technique. The H2O2 reduction on iron under these conditions was found to occur on the oxidized surfaces. The E-j polarization curves showed a significant hysteresis which is due to oxide film formation. On less oxidized and/or prereduced surfaces the H2O2 reduction was found to be faster than on more oxidized and/or prepassive surfaces. The reaction order with respect to H2O2 was found to be one. The rate determining step most likely involves the transfer of the first electron to the molecular H2O2. The ionic peroxide form HO-2 was not observed to be an electroactive species. The H2O2 reduction was found to be pH dependent at pH > 11. The observed pH dependence mostly reflects the acid-base equilibrium properties of H2O2 and partially those of the passive iron oxide film. Chloride ions were found not to have any influence on the reaction kinetics.