The influence of pH on reaction pathways for O2 reduction on the Au(100) face

Oxygen reduction on the Au(100) face was studied by the rotating disk-ring electrode technique in solutions of anions which adsorb strongly on gold (HSO₄^?/SO₄^2? and/or OH^?) over the entire pH range. The specific adsorption of OH^? anions, which is a pH dependent process, is found to play the key role in determining the reaction pathways. In the absence of OH^? adsorption, for pHs below 6, the reduction of O₂ begins as a 2e-process. Due to the increase in local pH during O₂ reduction, the reaction pathway turns into a 4e-reduction at a certain potential depending on the pH of the solution. For pHs higher than 6, O₂ reduction begins as a 4e-process in the potential region where specifically adsorbed OH^? anions are present.