Pt x Ir100–x thin films (8 nm thick) were deposited on MgO(100) substrates by pulsed laser deposition at 600 °C. As shown by X-ray diffraction and X-ray photoelectron spectroscopy analyses, the formation of fcc bulk and surface PtIr solid solution was observed over the whole compositional range despite the large miscibility gap exhibited by these elements below ca. 1000 °C. Moreover, pole figures indicate that all films exhibit a Pt(001)[010]//[010](001)­MgO cube-on-cube epitaxial relationship, which is consistent with AFM images. Cyclic voltammetry measurements performed in alkaline solutions confirmed both the presence of Ir atoms at the surface and the (100) surface orientation of all Pt x Ir100–x surfaces. The highest electrocatalytic activity for the electrooxidation of NH3 was observed for the Pt74Ir26(100) surface with a current density of ca. 1.0 mA cm–2 at 0.71 V vs RHE, which is 25% higher than that on Pt(100). The reasons underlying this behavior are discussed.

Pulsed laser deposition was used to grow thin layers of Pt on (001)-oriented MgO substrate. The deposition temperature was varied from −25 to 600 °C, and the film thickness was varied from ca. 7 to 45 nm. The crystalline quality, orientation, and epitaxial relationship of Pt thin films on (001)-oriented MgO substrate were investigated by atomic force microscopy and X-ray diffraction as well as through electrochemical probe reactions that are sensitive to the surface crystallographic orientations (H adsorption/desorption) and the width of the (100) terrace (NH 3 electro-oxidation reaction). All thin (7 nm thick) Pt films exhibit only one diffraction peak (the (001) peak) and a 4fold in-plane symmetry, indicating epitaxial growth is achieved independently of the deposition temperature. Moreover, the pole figure indicates that all films exhibit a Pt(001)[010]//[010](001)MgO cube-on-cube epitaxial relationship, which is consistent with the AFM images. The films are prepared with nearly 60% of (100) sites, and the maximum width of the (100) terraces is nine atomic rows, attained at 325 °C.