Oxygen reduction pathway on an unpyrolyzed carbon-supported cobalt oxide nanoparticles-cobalt porphyrin (CoOx-CoP/C) was investigated by rotating disk electrode (RDE) in acidic medium. Koutecky-Levich plots revealed that contrary to carbon-supported cobalt porphyrin (CoP/C), CoOx-CoP/C catalyzes the reduction of oxygen via a 4-electron pathway. Further results showed that the cobalt oxide nanoparticles (CoOx/C) do not catalyze electroreduction of H2O2. The N4-Co center appeared then as the only catalytic active site, dismissing the hypothesis of bifunctional mechanism on CoOx-CoP/C. Interestingly, CoOx-CoP/C exhibits better electrocatalytic properties toward H2O2 reduction than CoP/C, pointing the peculiar role of inactive cobalt oxide nanoparticles. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.109204jes] All rights reserved.