Origin of Multiple Peaks in the Potentiodynamic Oxidation of CO Adlayers on Pt and Ru-Modified Pt Electrodes.

The study of the electrooxidation mechanism of CO(ad) on Pt based catalysts is very important for designing more effective CO-tolerant electrocatalysts for fuel cells. We have studied the origin of multiple peaks in the cyclic voltammograms of CO stripping from polycrystalline Pt and Ru modified polycrystalline Pt (Pt/Ru) surfaces in both acidic and alkaline media by differential electrochemical mass spectrometry (DEMS), DFT calculations, and kinetic Monte Carlo (KMC) simulations. A new CO(ad) electrooxidation kinetic model on heterogeneous Pt and Pt/Ru catalysts is proposed to account for the multiple peaks experimentally observed. In this model, OH species prefer to adsorb at low-coordination sites or Ru sites and, thus, suppress CO repopulation from high-coordination sites onto these sites. Therefore, CO(ad) oxidation occurs on different facets or regions, leading to multiplicity of CO stripping peaks. This work provides a new insight into the CO electrooxidation mechanism and kinetics on heterogeneous catalysts.