Electrocatalytic Oxygen Reduction Reaction on Perovskite Oxides: Series versus Direct Pathway

The mechanism of the oxygen reduction reaction (ORR) on LaCoO3 and La0.8Sr0.2MnO3 perovskite oxides is studied in 1 M NaOH by using the rotating ring disc electrode (RRDE) method. By combining experimental studies with kinetic modeling, it was demonstrated that on perovskite, as well as on perovskite/carbon electrodes, the ORR follows a series pathway through the intermediate formation of hydrogen peroxide. The escape of this intermediate from the electrode strongly depends on: 1) The loading of perovskite; high loadings lead to an overall 4 e− oxygen reduction due to efficient hydrogen peroxide re‐adsorption on the active sites and its further reduction. 2) The addition of carbon to the catalytic layer, which affects both the utilization of the perovskite surface and the production of hydrogen peroxide. 3) The type of oxide; La0.8Sr0.2MnO3 displays higher (compared to LaCoO3) activity in the reduction of oxygen to hydrogen peroxide and in the reduction/oxidation of the latter. Genesis of hydrogen peroxide: Rotating ring disc electrode studies combined with kinetic modeling show that transition‐metal cations of perovskite oxides mediate the chemical and electrochemical steps of the oxygen reduction reaction through a series pathway. Escape of HO2− depends on the nature and loading of the oxide and on the presence of carbon; the latter affecting the formation of HO2− and the utilization of oxide.