Electrochemical and Electronic Properties of Platinum Deposits on Ru(0001): Combined XPS and Cyclic Voltammetric Study

We report a combined X-ray photoelectron spectroscopy (XPS) and cyclic voltammetric study of Ru(0001) electrodes covered by platinum. The Ru(0001) surfaces were prepared in ultrahigh vacuum, transferred to an electrochemical cell, and covered with platinum using either spontaneous deposition or electrolysis tactics. The Pt 4f 7/2 core level binding energies of the Pt/Ru(0001) electrodes prepared in this way were next studied as a function of Pt coverage. At 0.05 monolayer (ML), the binding energy is shifted by ca. 0.5 eV with respect to bulk Pt, but the shift decreases by 0.4 eV when the Pt coverage increases from 0.05 to 0.5 ML. The binding energy shifts are discussed in terms of the contributions from charge transfer and from lattice strain. We also studied the modes of growth of Pt islands on Ru(0001) by comparing estimates of the Pt coverage obtained from XPS and from cyclic voltammetry. At low Pt coverage, the islands have a monolayer height, but multilayer growth begins at a coverage of approximately 0.3 ML.