Electrosorption and catalytic properties of bare and Pt modified single crystal and nanostructured Ru surfaces

The electrosorption and catalytic properties of bare and Pt modified Ru(0001) and Ru(10−10) single crystal surfaces and carbon supported Ru nanoparticles have been studied by electrochemical, surface X-ray scattering, scanning tunneling microscopy, Fourier transform infrared spectroscopy and high resolution transmission electron microscopy techniques. The electrochemical surface oxidation of Ru(0001) in H2SO4 is an one-electron process resulting in 1 monolayer oxygen uptake and the increased spacing between the top two Ru layers from 2.13 Å at 0.1 V to 2.20 Å at 1.0 V. About 1/3 monolayer of bisulfate anions are coadsorbed with hydronium cations at low potentials. In HClO4 solution, the adsorption process at ∼0.1 V is due to the surface oxidation apparently to RuOH rather than to hydrogen adsorption. The oxidation of Ru(10−10) is quite facile and a progressive growth of the oxide layer is observed in repeated potential cycles. Spontaneous deposition of a submonolayer-to-multilayer of Pt on metallic Ru surfaces is a new phenomenon involving a noble metal deposition on a noble metal substrate through a local cell mechanism. The electrocatalysts prepared by spontaneous deposition of Pt on Ru nanoparticles have high activity and high CO tolerance exceeding those of the state-of-the-art commercial catalysts containing several times higher Pt loadings. Electronic effects appear to play a role in providing enhanced CO tolerance of Pt submonolayers on Ru nanoparticles.