The electroreduction of O-2 has been investigated at a bare glassy carbon (GC) electrode and a polyvinylferrocene (PVF) coated glassy carbon electrode (PVF-GC) in both 0.1 M NaClO4 Solution and phosphate buffer solutions of various pH values by using cyclic voltammetry and chronoamperometry. Two well-defined reduction peaks were observed at about -0.55 and -0.80 V versus SCE at PVF-GC electrode while one reduction peak was observed at about -0.85 V versus SCE at GC electrode in 0.1 M NaClO4 solution and phosphate buffer solutions of pH > 6. Two peaks at PVF-GC electrode indicated a two-step four-electron pathway of O-2 in these mediums. The first peak was ascribable to the two-electron reduction of O-2 to H2O2, while the second peak was assigned to the reduction of H2O2 to H2O. The electrocatalytic effects of PVF matrix for the reduction O-2 and the reduction of H2O2 were observed. The effects of the film thickness, O-2 concentration, pH and potential scan rates were investigated. (c) 2005 Elsevier B.V. All rights reserved.