Electroreduction of oxygen on Fe3O4 electrodes. Part 2.—Rotating ring–disc electrode studies and mechanism

Abstract

A complete kinetic study of oxygen electroreduction on Fe₃O₄ electrodes is presented and the results are analysed with a general kinetic scheme that includes intermediate peroxide reduction (k₃), heterogeneous disproportionation (k₄), adsorption (k₆) and desorption (k₅). The kinetic analysis takes into account the chemistry of Fe^II at the oxide surface. The reduction of oxygen follows an electrochemical–chemical–electrochemical (ECE) mechanism with the chemical oxidation of surface Fe^II by O₂ and the electrochemical reduction of the Fe^III site. The kinetic similarities of the cathodic reduction of oxygen on other Fe^II systems, such as passive iron and iron-macrocycle-modified electrodes, are discussed.