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Gas-Induced Segregation in a Pt-Rh Alloy Nanoparticle Revealed by In Situ Coherent X-ray Diffraction Imaging

  • Thomas Keller (DESY/Hamburg University, Germany)
Date
Monday 30 March 2020
Time
Address
Hotel NH Noordwijk Conference Centre Leeuwenhorst

Thomas F. Kellera,b, Tomoya Kawaguchic,d, Henning Rungea,b, Luca Gelisioa, Christoph Seitza, Young Yong Kima, Evan R. Maxeye, Wonsuk Chae, Andrew Ulvestadc, Stephan O. Hruszkewyczc, Ross Hardere, Ivan A. Vartanyantsa,f, Andreas Stierlea,b, Hoydoo Youc

a Deutsches Elektronen-Synchrotron DESY, D-22603 Hamburg, Germany
b Physics Department, Universit├Ąt Hamburg, D-20355 Hamburg, Germany
c Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
d Institute for Materials Research, Tohoku University, Sendai, 9808577, Japan
e Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
f National Research Nuclear University MEPhI, 115409 Moscow, Russia

Bimetallic catalysts can undergo segregation or redistribution of the metals driven by oxidizing and reducing environments. Bragg coherent X-ray diffraction imaging (CXDI) was used to relate displacement fields to compositional distributions in the crystalline Pt-Rh alloy nanoparticle shown in the scanning electron microscopy (SEM) image in Fig. 1a. Three-dimensional images of the internal composition reconstructed from the CXDI scans showed that the radial distribution of compositions zreverses partially between the surface shell and the core when gas flow changes between O2 and H2, as sketched in Figs. 1b-d.

Fig. 1.: a) SEM image of the analysed, sapphire-supported PtRh alloy nanoparticle, b-d) sketch of the PtRh alloy nanoparticle with the surrounding smaller Rh nanoparticles, under b) inert He, c) O2 and d) H2 environment.

Hierarchical Pt fiducial markers were applied by ion- (IBID) and electron- (EBID) beam induced deposition of a Pt precursor in the vicinity of the selected nanoparticle and used to re-locate the same particle in the SEM and in the X-ray beam using a confocal microscope.

Our observation suggests that the elemental segregation of nanoparticle catalysts is likely to be highly active during heterogeneous catalysis and can be a controlling factor in synthesis of electrocatalysts. In addition, our study exemplifies applications of CXDI for in situ 3D imaging of internal equilibrium compositions in other bimetallic alloy nanoparticles.

Acknowledgements

The authors acknowledge support from the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences Engineering Division and the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. The authors also acknowledge support from the EU-H2020 research and innovation program under Grant Agreement No. 654360 Nanoscience Foundries and Fine Analysis (NFFA Europe) and the Helmholtz Associations Initiative and Networking Fund and the Russian Science Foundation, Grant No. HRSF-0002. The use of the FIB dual beam instrument granted by BMBF (5K13WC3, PT-DESY) is acknowledged. One of the authors (T. K.) thanks the Japanese Society for the Promotion of Science (JSPS) for JSPS Postdoctoral Fellowships for Research Abroad.

References

  1. T. Kawaguchi, T. F. Keller, et al., Physical Review Letters, 2019, 123, 246001.
  2. M. Abuin, Y. Y. Kim, et al., ACS Applied Nano Materials 2019, 2, 4818-4824.
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