Double channel electrode flow cell application to the study of HO2− production on MnxCo3−xO4 (0 ≤ x ≤ 1) spinel films

We conducted a study on the electroreduction of O2 in alkaline solution at room temperature on pure thin oxide electrodes of composition MnxCo3−xO4 (0 ≤ x ≤ 1) using the double channel electrode flow cell (DCEFC). The oxides were prepared at 150 °C and deposited by spray pyrolysis onto titanium substrates. The oxygen reduction reaction (orr) occurs through “interactive” and “parallel” pathways, and the ratio of O2 molecules reduced to OH− ions with respect to those reduced to HO2− ions depends on the oxide stoichiometry and on the applied overpotential. The formation of HO2− increases when the manganese concentration increases. The results obtained for the orr show that the number of electrons transferred per O2 molecule decreases from 3 to 2 and the ratio k1/k2 (the rate constants for direct reduction to OH− and indirect reduction to HO2−) increases, respectively, in the overpotential studied range (−0.05 to −0.6 V). The Mn3+ ions placed in the B-sites of the spinel structure seem to be the active centres, where hydrogen peroxide is formed.