Oxygen reduction on iron-V. Processes in boric acid-borate buffer solutions in the 7.4-9.8 pH range

Abstract

O2 and H2O2 reduction was studied on Puratronic iron (99.995%) in borate buffer solutions of various pH ranging from 7.4 to 9.8. In solutions of pH < 9.3 the E-j curves are of quite irregular shapes and the limiting current is not established. Yet, in the potential region of the passivation-depassivation peak, a decrease in O2 and H2O2 reduction currents over time was observed. The influence of the passivation parameters (potential, time, speed, atmosphere and presence of H2O2 in the solution) on the degree of the inhibition of O2 and H2O2 reductions was examined. The loss of the electrocatalytic activity of the iron electrode is suggested to be due to the reaction between H2O2 and Fe(II) ions during the iron dissolution process occurring under the passivation-depassivation peak. The product of this reaction is an unconductive film which blocks the active electrode surface.