In situ surface-enhanced Raman spectroscopic studies of CO adsorption and methanol oxidation on Ru-modified Pt surfaces

Ru-modified Pt is so far the best catalyst for the anode reaction of direct. methanol fuel cells. The role of Ru is believed to promote carbon monoxide oxidation through a bifunctional mechanism and an electronic effect. However, direct experimental evidence for the electronic effect is sparse. In addition, whether Ru oxides or metallic Ru is the active component in the catalyst is still under debate. To address these issues, carbon monoxide adsorption and methanol oxidation on Ru-modified Pt thin film surfaces in acidic media were studied using in situ overlayer surface-enhanced Raman spectroscopy (SERS). Cyclic voltammograms show that with the presence of Ru, CO and methanol oxidation is significantly enhanced as evident by the negative shift of the oxidation potential. The addition of Ru to Pt surfaces did not change the Pt-CO stretching frequency, suggesting that the Pt-CO bond is not weakened significantly by Ru. Through combined SERS and cyclic voltammetry studies, we found that Pt and Ru oxides are inhibitors for methanol oxidation. In particular, Ru oxides on Ru-modified Pt strongly inhibit methanol oxidation on Pt sites, even when the Pt sites are in the metallic state.