Electrocatalytic reduction of molecular oxygen at electrodes coated with a new cobalt(II)–platinum(II) bimetallic porphyrin

Abstract

Cobalt(II) inserts into 5-(4-pyridyl)-10,15,20-(3,4-dimethoxyphenyl)porphyrin (1) by reaction of the porphyrin with the cobalt(II) acetate salt in refluxing N,N′-dimethylformamide solutions. When the porphyrin and the cobalt porphyrin are reacted with PtCl2(DMSO)2 in dichloromethane at ambient temperatures the platinum complex coordinates to the peripheral pyridyl group of the porphyrin. Roughened EPG electrodes coated with the cobalt(II)–platinum(II) bimetallic porphyrin, complex (4), show a 500 mV shift in the reduction of molecular oxygen in acidic media when compared to the bare electrode. Oxidation of the bimetallic porphyrin coated electrodes at 1.20 V versus saturated calomel electrode (SCE) results in an additional shift of ca 100 mV for the reduction of molecular oxygen when compared to the bimetallic porphyrin coated electrode prior to oxidation. In addition the oxidized surface shows the ability to reduce approximately 50% of the oxygen to water and the other 50% to hydrogen peroxide according to rotating disk electrode measurements.