The mechanism of the oxygen redn. reaction (orr) was studied in alk. media at La0.6Ca0.4CoO3-activated carbon electrodes in a channel flow cell (CFC). The electrodes were made by depositing a mixt. of the perovskite (La0.6Ca0.4CoO3) powder as the catalyst, Vulcan XC 72 as the carbon, and Triton X-100 as the binder on Ti substrates. The collection efficiency, N, of the double-electrode system in the CFC was evaluated in advance using the ferro-ferricyanide couple. The results obtained for the orr show that the mean no. of electrons transferred per O2 mol., ng, remains around 2, while the ratio k1/k2 (the rate consts. for direct redn. to OH- and indirect redn. to HO2-) is much smaller than 1, both at nonactivated and perovskite-activated carbon electrodes. This indicates that most of the oxygen was reduced via the two-electron pathway to HO2-. The hydrogen peroxide ions appear to be stable at Vulcan, but are further reduced and/or chem. decompd. in part in the presence of the metal-oxide catalyst. [on SciFinder (R)]