Bulk Metal Electrodeposition in the Sub-monolayer Regime: Ru on Pt(111)

The potentiostatic electrodeposition of Ru from acidic solutions of RuCl., was investigated over a wide range of deposition potentials. At potentials below 0.25 V, a massive growth of Ru metal occurs. In the potential range 0.3 V ≤ E_dep ≤ 0.8 V submonolayer amounts of Ru are deposited, with the surface coverage increasing linearly with decreasing potential. The relation between deposition potential and surface coverage is determined quantitatively via ex situ XPS measurements. The anomalous deposition kinetics are attributed to an inhibitive influence of adsorbing Cl^- ions. The submonolayer electrodeposits are composed of Ru islands with 2 to 5 nm diameter and monoatomic height, as determined by electrochemical scanning tunneling microscopy and confirmed by X-ray surface diffraction. The electrocatalytic properties of the well-characterized model electrodes regarding the oxidation of adsorbed monolayers of carbon monoxide are investigated with conventional electrochemical techniques and vibrational spectroscopy. The enhancement of the catalytic properties of Pt(111) by the Ru islands is evidence that surface diffusion of adsorbed CO is essential for the understanding of the electrooxidation kinetics.