Atomic-Scale Snapshots of the Formation and Growth of Hollow PtNi/C Nanocatalysts.
Determining the formation and growth mechanism of bimetallic nanoparticles (NPs) with atomic detail is fundamental to synthesize efficient "catalysts by design". However, an understanding of the elementary steps which take place during their synthesis remains elusive. Herein, we have exploited scanning transmission electron microscopy coupled to energy-dispersive X-ray spectroscopy, operando wide angle and small-angle X-ray scattering, and electrochemistry to unveil the formation and growth mechanism of hollow PtNi/C NPs. Such NPs, composed of a PtNi shell surrounding a nanoscale void, catalyze efficiently and sustainably the oxygen reduction reaction (ORR) in an acidic electrolyte. Our step-by-step study reveals that (i) Ni-rich/C NPs form first, before being embedded in a NixByOzshell, (ii) the combined action of galvanic displacement and the nanoscale Kirkendall effect then results in the sequential formation of Ni-rich core@Pt-rich/C shell and ultimately hollow PtNi/C NPs. The electrocatalytic properties for the ORR and the stability of the different synthesis intermediates were tested and structure-activity-stability relationships established both in acidic and alkaline electrolytes. Beyond its interest for the ORR electrocatalysis, this study also presents a methodology that is capable to unravel the formation and growth mechanism of various nanomaterials including preferentially shaped metal NPs, core@shell NPs, onion-like NPs, Janus NPs, or a combination of several of these structures.
Univ. Grenoble Alpes, LEPMI , F-38000 Grenoble, France.|CNRS, LEPMI , F-38000 Grenoble, France.
Raphaël
R
Chattot
Univ. Grenoble Alpes, LEPMI , F-38000 Grenoble, France.|CNRS, LEPMI , F-38000 Grenoble, France.
Tristan
T
Asset
European Synchrotron Radiation Facility , ID 31 Beamline, BP 220, F-38043 Grenoble Cedex, France.
Jakub
J
Drnec
Université Grenoble Alpes, Institut Néel , F-38000 Grenoble, France.|CNRS, Institut Néel , F-38000 Grenoble, France.
Pierre
P
Bordet
Université Paris Diderot, Sorbonne Paris Cité, CNRS, Laboratoire Matériaux et Phénomènes Quantiques, UMR 7162, F-75013, Paris, France.
Jaysen
J
Nelayah
Univ. Grenoble Alpes, LEPMI , F-38000 Grenoble, France.|CNRS, LEPMI , F-38000 Grenoble, France.
Laetitia
L
Dubau
Univ. Grenoble Alpes, LEPMI , F-38000 Grenoble, France.|CNRS, LEPMI , F-38000 Grenoble, France.
Frédéric
0000-0002-6470-8900
F
Maillard
Operando identification of synthesis intermediates; galvanic replacement; hollow PtNi NPs; nanoscale Kirkendall effect; oxygen reduction reaction