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 02 in alkaline solution at room temperature on pure thin oxide electrodes of composition MnxCO(3-x) (0 <= x <= 1) using the double channel electrode flow cell (DCEFC). The oxides were prepared at 150 degrees C and deposited by spray pyrolysis onto titanium substrates. The oxygen reduction reaction (orr) occurs through "interactive" and "parallel" pathways, and the ratio of O-2 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 O-2 molecule decreases from 3 to 2 and the ratio k(1)/k(2) (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. (c) 2004 Elsevier Ltd. All rights reserved.