부산대학교 도서관

To reveal the origin of the difference between the Pt–Pt bond distance in Au(core)–Pt(shell)-type (PtAu) nanoparticles and that in a Pt overlayer on Au(111), alloy-type PtAu nanoparticles were prepared on a highly oriented pyrolytic graphite (HOPG) surface by arc plasma deposition and their structure was investigated under various electrochemical conditions by bent-crystal Laue analyzer (BCLA)-empowered back-illuminated X-ray absorption fine structure (BCLA + BI-XAFS) and high-energy-resolution fluorescence detection (HERFD)-empowered back-illuminated X-ray absorption near-edge structure (HERFD + BI-XANES) methods. On the basis of the XAFS analysis at both edges, we proposed the formation of a PtAu alloy core covered with a Pt-rich shell at 0.4 VRHE, where the Pt–Pt, Pt–Au, and Au–Au bond lengths were all found to be ∼2.76 Å. The Au–Au bond length was abnormally shorter than that for bulk Au. The Pt shell was dissolved under applied potentials greater than 0.8 VRHEwith the aid of the high-intensity X-rays, and the Au–Au distance increased. We concluded that the abnormal bond lengths were due to the strong surface tension from the Pt-rich shell and the relaxation of the lattice distortion. The Pt–Pt bond length in the PtAu nanoparticles decreases as a result of the surface tension of the nanoparticles; this surface tension does not exist on flat Au surfaces, where the lattice distortion between the Pt overlayer and the substrate is the main driving force for the expansion of the Pt–Pt bond length.