Enhanced Electrocatalytic Reduction of Oxygen at Electrodes Coated with a Multi-Metallic Co(II)/Pt(II) Porphyrin

Edge plane pyrolytic graphite (EPG) electrodes coated with the Co(II)/Pt(II)₂ analog of 5,15-bis-(4-pyridyl)-10,20-bis-(3-methoxy-4-hydroxyphenyl)porphyrin undergo an electrochemical-chemical-electrochemical (ECE) reaction when anodically scanned in 1.0 M sulfuric acid. The new redox couple formed from this anodic conditioning of the coated electrode is dependent on the pH of the solution. Roughened EPG electrodes coated with the Co(II)/Pt(II)₂ trimetallic porphyrin show a catalytic shift of 400 mV for the reduction of O₂ when compared to the reduction of O₂ at a bare EPG electrode. An additional catalytic shift of ca. 150 mV is observed for O₂ reduction at an EPG electrode coated with the Co(II)/Pt(II)₂ porphyrin which has been oxidized in 1.0 M sulfuric acid. In addition to the added electrocatalysis a significant percentage of O₂ reduced at the oxidized Co(II)/Pt(II)₂ EPG electrode is converted to H₂O as determined by rotating disk electrode measurements.