Identification of CO adsorbed at Ru and Pt sites on a polycrystalline Pt/Ru electrode and the observation of their oxidation and free interchange under open circuit conditions

The spontaneous oxidation of CO adsorbates on a Pt electrode modified by Ru under open circuit (OC) conditions in perchloric acid solution has been followed, for the first time, using in situ FTIR spectroscopy, and the dynamics of the surface processes taking place have been elucidated. The IR data show that adsorbed CO present on both the Ru and Pt domains and can be oxidized by the oxygen-containing adlayer on the Ru in a chemical process to produce CO2 under OC conditions. There is a free exchange of COads between the Ru and Pt sites. Oxidation of COads may take place at the edges of the Ru islands, but COads transfer, at least on the time scale of these experiments, allows the two different populations to maintain equilibrium. Oxidation is limited in this region by the rate of supply of oxygen to the surface of the catalyst. A mechanism is postulated to explain the observed behavior.