%0 Journal Article
%A Beermann, Vera
%A Gocyla, Martin
%A Kühl, Stefanie
%A Padgett, Elliot
%A Schmies, Henrike
%A Goerlin, Mikaela
%A Erini, Nina
%A Shviro, Meital
%A Heggen, Marc
%A Dunin-Borkowski, Rafal
%A Muller, David A.
%A Strasser, Peter
%T Tuning the Electrocatalytic Oxygen Reduction Reaction Activity and Stability of Shape-Controlled Pt–Ni Nanoparticles by Thermal Annealing − Elucidating the Surface Atomic Structural and Compositional Changes
%J Journal of the American Chemical Society
%V 139
%N 46
%@ 1520-5126
%C Washington, DC
%I American Chemical Society
%M FZJ-2018-00779
%P 16536 - 16547
%D 2017
%X Shape-controlled octahedral Pt–Ni alloy nanoparticles exhibit remarkably high activities for the electroreduction of molecular oxygen (oxygen reduction reaction, ORR), which makes them fuel-cell cathode catalysts with exceptional potential. To unfold their full and optimized catalytic activity and stability, however, the nano-octahedra require post-synthesis thermal treatments, which alter the surface atomic structure and composition of the crystal facets. Here, we address and strive to elucidate the underlying surface chemical processes using a combination of ex situ analytical techniques with in situ transmission electron microscopy (TEM), in situ X-ray diffraction (XRD), and in situ electrochemical Fourier transformed infrared (FTIR) experiments. We present a robust fundamental correlation between annealing temperature and catalytic activity, where a ∼25 times higher ORR activity than for commercial Pt/C (2.7 A mgPt–1 at 0.9 VRHE) was reproducibly observed upon annealing at 300 °C. The electrochemical stability, however, peaked out at the most severe heat treatments at 500 °C. Aberration-corrected scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy (EDX) in combination with in situ electrochemical CO stripping/FTIR data revealed subtle, but important, differences in the formation and chemical nature of Pt-rich and Ni-rich surface domains in the octahedral (111) facets. Estimating trends in surface chemisorption energies from in situ electrochemical CO/FTIR investigations suggested that balanced annealing generates an optimal degree of Pt surface enrichment, while the others exhibited mostly Ni-rich facets. The insights from our study are quite generally valid and aid in developing suitable post-synthesis thermal treatments for other alloy nanocatalysts as well.
%F PUB:(DE-HGF)16
%9 Journal Article
%$ pmid:29019692
%U <Go to ISI:>//WOS:000416496400025
%R 10.1021/jacs.7b06846
%U https://juser.fz-juelich.de/record/842560