The role of anions in oxygen reduction in neutral and basic media on gold single-crystal electrodes

Oxygen reduction on well-defined single-crystal electrodes in different basic and neutral media has been studied using the impinging jet system. The results obtained with this system in 0.1 M NaOH are comparable to those reported in the literature for rotating disk electrodes, indicating that the impinging jet system behaves as a system in which the thickness of the diffusion layer is stationary. The activity of the Au(100) electrode is considerably higher than the rest of the basal planes in all media and yields water when E>-0.2 V and hydrogen peroxide for E<-0.2 V on the SHE scale. For Au(111) and Au(110) the activity of the electrode is much smaller and the final product is always hydrogen peroxide. The transition between both mechanisms for the Au(100) is, essentially, independent of the solution pH. In acid media the final product is always hydrogen peroxide for all the electrodes studied. The differences between the activities of the electrodes have been explained in the light of the different adsorption properties of the surfaces in relation to HO2-. In the case of the Au(100) electrode, the existence of a negative charge density on the metal inhibits further reduction of HO2-.