Oxygen electroreduction on chemically modified glassy carbon electrodes in alkaline solution

The electrochemical reduction of oxygen on glassy carbon (GC) electrodes modified with aryl groups has been studied using the rotating disk electrode (RDE) technique. The GC electrodes were grafted by electrochemical reduction of diazonium salts. The diazonium derivatives of benzene, naphthalene and anthracene were used in surface modification. The blocking behaviour of aryl layers towards oxygen reduction was investigated. An unexpected order of blocking efficiency of the aryl moieties was observed for O2 reduction in 0.1 M KOH. The phenyl-modified GC electrode was less active than those electrografted with naphthalene and anthracene. Comparative measurements were carried out in 1 mM K3Fe(CN)6. A much larger extent of blocking was evident for the Fe(CN)63-/4- couple. This effect was explained by a significant difference in size between the Fe(CN)63-/4- ions and O2 molecule. A mixed film of anthraquinone (AQ) and phenyl groups was formed by diazonium reduction and its relevance in the kinetics investigations was discussed. The kinetic parameters of oxygen reduction were determined using a surface redox catalytic cycle model for quinone-modified electrodes.