Binding energy of ruthenium submonolayers deposited on a Pt(111) electrode

We investigated the 3d(5/2) core-level binding energy of Ru in Ru nanoislands spontaneously deposited on a Pt(111) electrode [Pt(111)/Ru], and the binding energies of 3d(5/2) iodine and 1s CO adsorbed on Pt(111)/ Ru by the use of X-ray photoelectron spectroscopy. Both iodine and CO were used as surface probes of the electronic properties of Pt(111)/Ru. Little difference was found in the binding energy of Ru in Pt(111)/Ru and in Ru(0001). However, the addition of Ru to Pt(111) induces major changes in the core-level binding energies of chemisorbed iodine and CO as referenced to those adsorbed on Ru(0001). We conclude that the iodine 3d(5)/ 2 and CO 1s C core levels experience higher electronic charge on Pt(111)/Ru than on Ru(0001), suggesting a charge transfer from Pt to Ru, or to a Ru-I "surface molecule" within the deposit. The charge transfer from Pt to Ru is in agreement with the result of previous in situ electrochemical NMR investigations [P.K. Babu, H.S. Kim, A. Wieckowski, E. Oldfield (2003) J. Phys. Chem. B 107:7595] and confirms the general trend of reduction in the density of states of Pt due to alloying with Ru [J. McBreen, S. Mukerjee (1995) J. Electrochem. Soc. 142:3399]. Theoretical calculations are in progress to further interpret the origin of the binding-energy shifts observed in this study.