The mechanism of oxygen reduction on iron in neutral solutions

The pathways and rate-determining steps of oxygen reduction on iron in neutral pH range have been i vestigated. The various mechanistic criteria are obtained as a function of the nature of the electrode surface: bare iron and passive iron. The oxygen reduction on bare iron proceeds through 4e pathways with little hydrogen peroxide as an intermediate and formation of superoxide radical in the rds. On passive iron, oxygen reduction proceeds through a 2e- pathway with the formation of hydrogen peroxide as a reaction product. An rds involving chemisorption of oxygen is suggested. Although the anodic reactions for metal and alloy (1-5) dissolution have been extensively studied in solutions of various pH's, the pert inent cathodic processes have re-ceived little attention in the intermediate pH range (6, 7). Generally, under practical conditions, the cathodic reac-tion of hydrogen evolution is the depolarization reaction in acidic solutions, whereas the oxygen reduct ion reac-tion acts as a depolarizer in neutral and alkaline solution. The principal diff iculty general ly considered to con