Electrooxidation of Fe, Co, Ni and Cu Metalloporphyrins on Edge‐Plane Pyrolytic Graphite Electrodes and Their Electrocatalytic Ability towards the Reduction of Molecular Oxygen in Acidic Media

Edge‐plane pyrolytic graphite (EPG) electrodes coated with5,10,15,20‐tetrakis(4‐hydroxy‐3‐methoxyphenyl)porphyrin[H 2 T3M4HPP] and its Fe III , Co II , Ni II and Cu II analogs undergo an electrochemical/chemical/electrochemical (ECE) reaction when anodically scanned in 0.5 M H 2 SO 4 . 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 metalloporphyrins show a catalytic shift for the reduction of O 2 when compared to the reduction of O 2 at a bare EPG electrode. An additional catalytic shift of approximately 100 mV is observed for O 2 reduction at an EPG electrode coated with the Co II porphyrin, which has been oxidized in 0.5 M H 2 SO 4 . In addition to the added electrocatalysis, approximately 15 % of the O 2 reduced at the oxidized Co II porphyrin EPG electrode is converted to H 2 O as determined by rotating‐disk electrode measurements.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)