Tuning Pt-Ir Interactions for NH3 Electrocatalysis

PtxIr100-x thin films (8 nm thick) were deposited on MgO(100) substrates by pulsed laser deposition at 600 degrees C. As shown by X-ray diffraction and X-ray photoelectron spectroscopy analyses, the formation of fcc bulk and surface Pt-Ir solid solution was observed over the whole compositional range despite the large miscibility gap exhibited by these elements below ca. 1000 degrees 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 PtxIr100-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.