Synthesis and Characterization of Cu-Pt Bimetallic Nanoparticles

ed: Pt-based alloys have recently triggered a lot of attentions due to their important potential industrial applications. They provide great opportunities for the development of low-cost and high-performance fuel-cell catalysts. Many studies have already pointed out the excellent physico-chemical properties of Pt-based alloys, intimately related to their internal structure. Great efforts have been spent to characterize shape, homogeneity, dispersion, alloying extent and kinetic growth of Pt-based nano-particles. Here, we present Cu-Pt bimetallic nano-particles synthesized by the thermal decomposition method under oleylamine and OE coordination. HRTEM images show that Cu-Pt nanostructures having size of about 1.2 nm includes about 35 atoms capped by the surfactant with OA. Accurate structural information of this system has been obtained by XRD and XAFS. A charge transfer mechanism has been observed and Pt occupied Cu sites in these Cu-Pt nanoparticles. Introduction An increasing attention has been devoted to Pt-based alloys due to their important potential industrial applications, which provide a great opportunity for the development of low-cost and high-performance industrial fuel-cell catalysts. A variety of Pt-Me (Me: Metal) alloy nano-particles (NPs) such as Pt-Cu, Pt-Fe, Pt-Co, Pt-Mn have been synthesized with a precise control of size, shape and chemical composition. These Pt-based alloys exhibit perfect properties hardly achievable by Pt metal Pt, especially in catalytic reactors . Excellent physico-chemical properties of Pt-Me alloy nano-particles depend on several factors, such as the extent of the alloying or the atomic distribution and the surface segregation of the particles ; the particle homogeneity and structure and shape of particles ; the ensemble effect, ligand and geometrical effects in Pt-Me alloys . Therefore, in order to get the ultimate goal, i.e., the control of material properties, a lot of efforts have been devoted to characterize shape, homogeneity, dispersion, alloying extent, and kinetic growth of alloy nano-particles. Although it is well known that the structure of a material strongly influences its properties, it remains a challenge to understand both structure and dynamics of alloy nano-materials. It is then mandatory identify and set up accurate methods to characterize the internal structure of a bimetallic nano-particle [18] at the atomic level. 15th International Conference on X-ray Absorption Fine Structure (XAFS15) IOP Publishing Journal of Physics: Conference Series 430 (2013) 012037 doi:10.1088/1742-6596/430/1/012037 Published under licence by IOP Publishing Ltd 1 In this work, we focus on the structure of Cu-Pt nano-clusters with size of ~1 nm by using advanced X-ray absorption spectroscopy (XAS), combined with transmission electron microscopy (TEM) and X-ray diffraction (XRD). Since the catalytic activity of the bimetallic cluster is strongly affected by the structure, but also by the atomic distribution, we will try to provide precise details of the atomic distribution of Cu-Pt bimetallic clusters. Experimental Cu-Pt nano-crystals were synthesized in agreement with a previous reported [19] with some modifications. In brief, a ratio of molar Pt(acac)2 and Cu(acac)2, 210 mg of the 1,2-hexadecanediol, 0.6 ml of oleic acid and 0.4 ml of oleylamine were mixed together with 5 ml of 1-octadecene in a 100 ml three-neck round-bottom flask. The flask was purged with Ar, heated to 120 °C for 20 min and then heated to 225 °C at a rate of 20 °C/min. After 30 min, the black-colored solution was cooled to room temperature. The resultant products were isolated by centrifugation, washed with ethanol for several times and resolved in the hexane for the other measurements. Fig.1 TEM images of Cu2Pt1 (a) and Cu1Pt2 (b) nano-particles; (c) EDS of Cu-Pt nano-particles. The Cu-Pt alloy nano-crystals with different molar ratios have been characterized by XRD, TEM and XAS, i.e., both X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS). XRD measurements were performed using a PANalytical X’pert pro diffractometer using a graphite monochromatized Cu-Kα radiation source. Samples were also characterized with a JEOL JEM2100 transmission electron microscope operating at 200 keV. The samples for TEM were prepared by placing one drop of the hexane solution onto a carbon-coated Ni grid and allowing it to dry in air. XAS spectra at the Pt L3and Cu K-edge were collected in the transmission mode at the beamline U7C of the National Synchrotron Radiation Laboratory (NSRL, Hefei). The storage ring was working at the energy of 800 MeV with an average electron current of 150 mA. Hard X-rays were monochromatized with a Si(111) double-crystals monochromator. The incident and output beam intensities were recorded using ionization chambers filled by a 25% argon 15th International Conference on X-ray Absorption Fine Structure (XAFS15) IOP Publishing Journal of Physics: Conference Series 430 (2013) 012037 doi:10.1088/1742-6596/430/1/012037