OXYGEN REDUCTION ON AU(111) AND VICINAL AU(332) FACES - A ROTATING-DISC AND DISC-RING STUDY

The kinetics of oxygen reduction on the Au(Ill) surface in acidic solution has been reexamined by means of a rotating disc electrode technique. Its vicinal Au(332) = Au[6(111) x (111)] surface has been chosen to examine the role of a small density of steps as active sites. The increase of the average surface energy, caused by the presence of steps on the Au(332) face, causes a slight shift of the half-wave potential to a more positive value, compared to the Au(111). The reaction on Au(111) is kinetically hindered in the whole potential region up to hydrogen evolution. The presence of steps on the Au(332) face apparently causes the kinetic limitations to be lifted. The kinetics of oxygen reduction on the Au(332) face in alkaline solution has been studied by means of a rotating disc-ring method. The mechanism of the reaction has been found the simplest among all the faces of Au investigated so far. In the kinetic and mixed control regions the reduction proceeds through the simplest 2e-series pathway. At large overpotentials, a 4e-reduction occurs, whose extent depends on the potential, with a surface diffusion of HO2a- as a rate determining step. No splitting of the O-O bond has been found. A map of the reaction pathways for the whole potential range of oxygen reduction has been constructed.