Abnormal Metal Bond Distances in PtAu Alloy Nanoparticles: In Situ Back-Illumination XAFS Investigations of the Structure of PtAu Nanoparticles on a Flat HOPG Substrate Prepared by Arc Plasma Deposition
- Bing HuBing HuInstitute for Catalysis, Hokkaido University, Sapporo, Hokkaido 001-0021, JapanMore by Bing Hu,
- Bapurao BharateBapurao BharateInstitute for Catalysis, Hokkaido University, Sapporo, Hokkaido 001-0021, JapanMore by Bapurao Bharate,
- Juan D. JimenezJuan D. JimenezDepartment of Chemical Engineering, University of South Carolina, 541 Main Street, Columbia, South Carolina 29208, United StatesMore by Juan D. Jimenez,
- Jochen LauterbachJochen LauterbachDepartment of Chemical Engineering, University of South Carolina, 541 Main Street, Columbia, South Carolina 29208, United StatesMore by Jochen Lauterbach,
- Naoto TodorokiNaoto TodorokiGraduate School of Environmental Studies, Tohoku University, Sendai, Miyagi 980-8579, JapanMore by Naoto Todoroki,
- Toshimasa WadayamaToshimasa WadayamaGraduate School of Environmental Studies, Tohoku University, Sendai, Miyagi 980-8579, JapanMore by Toshimasa Wadayama,
- Kotaro HigashiKotaro HigashiInnovation Research Center for Fuel Cells, University of Electro-Communications, Chofu, Tokyo 182-8585, JapanMore by Kotaro Higashi,
- Tomoya UrugaTomoya UrugaInnovation Research Center for Fuel Cells, University of Electro-Communications, Chofu, Tokyo 182-8585, JapanJapan Synchrotron Radiation Research Institute (JASRI), Sayo, Hyogo 679-5148, JapanMore by Tomoya Uruga,
- Yasuhiro IwasawaYasuhiro IwasawaInnovation Research Center for Fuel Cells, University of Electro-Communications, Chofu, Tokyo 182-8585, JapanMore by Yasuhiro Iwasawa,
- Hiroko Ariga-MiwaHiroko Ariga-MiwaInnovation Research Center for Fuel Cells, University of Electro-Communications, Chofu, Tokyo 182-8585, JapanMore by Hiroko Ariga-Miwa,
- Satoru TakakusagiSatoru TakakusagiInstitute for Catalysis, Hokkaido University, Sapporo, Hokkaido 001-0021, JapanMore by Satoru Takakusagi, and
- Kiyotaka Asakura*Kiyotaka Asakura*Email: [email protected]Institute for Catalysis, Hokkaido University, Sapporo, Hokkaido 001-0021, JapanMore by Kiyotaka Asakura
Abstract
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 VRHE with 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.
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