Аннотация:The electroreduction of oxygen on a ruthenium phthalocyanine catalyst in 1.0 M KOH is studied by rotating ring-disc electrode (RRDE) method. The polarization curves display two plateau-like regions of the limiting current, which suggests a two-step mechanism of oxygen electroreduction including the formation of an intermediate peroxide ion. The analysis of the data in the Levich and Koutecký–Levich coordinates show that already in the range of the first wave potentials the formation of a peroxide ion is accompanied by the direct four-electron reduction of oxygen to water.