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

O 2 and H 2O 2 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 O 2 and H 2O 2 reduction currents over time was observed. The influence of the passivation parameters (potential, time, speed, atmosphere and presence of H 2O 2 in the solution) on the degree of the inhibition of O 2 and H 2O 2 reductions was examined. The loss of the electrocatalytic activity of the iron electrode is suggested to be due to the reaction between H 2O 2 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.