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@INPROCEEDINGS{Heggen:827180,
      author       = {Heggen, Marc and Gocyla, Martin and Gan, Lin and Strasser,
                      Peter and Dunin-Borkowski, Rafal},
      title        = {{G}rowth and degradation of advanced octahedral {P}t-alloy
                      nanoparticle catalysts for fuel cells},
      address      = {Weinheim, Germany},
      publisher    = {Wiley-VCH Verlag GmbH $\&$ Co. KGaA},
      reportid     = {FZJ-2017-01378},
      pages        = {800 - 801},
      year         = {2016},
      comment      = {European Microscopy Congress 2016: Proceedings},
      booktitle     = {European Microscopy Congress 2016:
                       Proceedings},
      abstract     = {Octahedral Pt-Ni nanoparticles are highly attractive as
                      fuel-cell catalysts due to their extraordinarily high
                      activity for the oxygen-reduction-reaction (ORR). A deep
                      understanding of their atomic-scale structure, degradation
                      and formation is a prerequisite for their use as rationally
                      designed nanoparticle catalysts with high activity and
                      long-term stability.Here we present an extensive
                      microstructural study of the growth and degradation behavior
                      of various octahedral Pt-alloy nanoparticles using in situ
                      transmission electron microscopy (TEM) and Cs-corrected
                      high-angle annular dark-field scanning transmission electron
                      microscopy (HAADF-STEM) combined with electron energy-loss
                      spectroscopy (EELS) and energy-dispersive X-ray spectroscopy
                      (EDX). We show that octahedral nanoparticles often show
                      compositional anisotropy with Ni-rich {111} facets leading
                      to complex structural degradation during ORR
                      electrocatalysis. The Ni-rich {111} facets are
                      preferentially etched, resulting in the formation of first
                      concave octahedra and then Pt-rich skeletons that have less
                      active facets (Figure 1)[1]. Furthermore, we reveal
                      element-specific anisotropic growth as the reason for the
                      compositional anisotropy and the limited stability. During
                      the solvothermal synthesis, a Pt-rich nucleus evolves into
                      precursor nanohexapods, followed by the slower step-induced
                      deposition of Ni on the concave hexapod surface, to form
                      octahedral facets (Figure 2)[2]. While the growth of Pt-rich
                      hexapod is a ligand-controlled kinetic process, the
                      step-induced deposition of the Ni-rich phase at the concave
                      surface resembles a thermodynamically controlled process
                      accomplished in much longer time. In order to tune the
                      atomic-scale microstructure of the octahedra for long-term
                      stability, we illustrate the effect of varying the growth
                      conditions on morphology and compositional segregation by
                      producing trimetallic PtNiCo nanooctahedra and comparing
                      “one-step” and newly-developed “two-step” synthesis
                      routes [3]. Furthermore we demonstrate how Pt atom surface
                      diffusion may produce a protective Pt surface layer on top
                      of the Ni-rich facets, resulting in advanced and more stable
                      octahedral catalysts. Figure 3 shows a sequence of
                      structural changes taking place on an octahedral
                      nanoparticle during in situ heating up to 800°C using a
                      MEMS chip heating holder (DENSsolutions, Delft, NL). It can
                      be observed that Pt-rich corner atoms diffuse and
                      subsequently fill the concave Ni-rich {111} facets, forming
                      perfectly octahedral nanoparticles with flat Pt-rich {111}
                      surfaces (Figure 3) [4].},
      month         = {Aug},
      date          = {2016-08-28},
      organization  = {16th European Microscopy Congress (EMC
                       2016), Lyon (France), 28 Aug 2016 - 2
                       Sep 2016},
      cin          = {PGI-5 / ER-C-1},
      cid          = {I:(DE-Juel1)PGI-5-20110106 / I:(DE-Juel1)ER-C-1-20170209},
      pnm          = {143 - Controlling Configuration-Based Phenomena (POF3-143)},
      pid          = {G:(DE-HGF)POF3-143},
      typ          = {PUB:(DE-HGF)8 / PUB:(DE-HGF)7},
      doi          = {10.1002/9783527808465.EMC2016.6030},
      url          = {https://juser.fz-juelich.de/record/827180},
}