Electrocatalytic reduction of oxygen at electrodes coated with a bimetallic cobalt(ii)/platinum(ii) porphyrin

Abstract

Edge plane pyrolytic graphite (EPG) electrodes coated with 5-(4-pyridyl)-10,15,20-tris(3-methoxy-4-hydroxyphenyl)porphyrin and its Pt(II) and Co(II)/Pt(II) analogs undergo an electrochemical–chemical–electrochemical (ECE) reaction when anodically scanned in 1.0 M HClO₄. 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) bimetallic porphyrin show a catalytic shift of 500 mV for the reduction of O₂ when compared to the reduction of O₂ at a bare EPG electrode. An additional catalytic shift of ca. 100 mV is observed for O₂ reduction at an EPG electrode coated with the Co(II)/Pt(II) porphyrin which has been oxidized in 1.0 M HClO₄. In addition to the added electrocatalysis a significant percentage of O₂ reduced at the oxidized Co(II)/Pt(II) EPG electrode is converted to H₂O as determined by rotating disk electrode measurements.