Shape-controlled synthesis of Pt-Ir nanocubes with preferential (100) orientation and their unusual enhanced electrocatalytic activities

Pt-Ir nanocubes with (100)-terminated facets were synthesized for the first time and their unusual high electrocatalytic activity for a model reaction (i.e., ammonia oxidation) was reported. The key parameters in controlling the shape of the Pt-Ir nanocubes were systematically investigated by transmission electron microscopy (TEM). The electrocatalytic activities of the prepared Pt-Ir and pure Pt nanoparticles (NPs) were characterized by cyclic voltammetry (CV). The results showed that the amount of W(CO)6 and the volume ratio of oleylamine and oleic acid play a significant role in the development of well-defined Pt-Ir nanocubes. The resultant Pt-Ir nanocubes exhibit (100) orientation, which has been confirmed by not only the structural characterization results from high-resolution TEM (HRTEM) and X-ray diffraction (XRD) but also hydrogen desorption profiles obtained from the CV measurements in H2SO4 solution. Lattice contraction of the Pt-Ir nanocubes were suggested by HRTEM and XRD measurements, and the electronic interactions between Pt and Ir in the Pt-Ir nanocubes were demonstrated by X-ray photoelectron spectroscopy. The Pt-Ir nanocubes show higher specific activity than pure Pt nanocubes and much higher specific activity than the polycrystalline Pt-Ir NPs. The much improved specific activity of the Pt-Ir nanocubes could be attributed to the reason that the introduction of Ir in the Pt-Ir nanocubes largely maintains the highly active Pt (100) sites and thus a positive synergistic effect through the addition of Ir to Pt could be achieved due to the possible bifunctional mechanism and the electronic effect.