Abstract
The catalytic performance of core-shell platinum alloy nanoparticles is typically superior to that of pure platinum nanoparticles for the oxygen reduction reaction in fuel cell cathodes. Thorough understanding of core-shell formation is critical for atomic-scale design and control of the platinum shell, which is known to be the structural feature responsible for the enhancement. Here we reveal details of a counter-intuitive core-shell formation process in platinum-cobalt nanoparticles at elevated temperature under oxygen at atmospheric pressure, by using advanced in situ electron microscopy. Initial segregation of a thin platinum, rather than cobalt oxide, surface layer occurs concurrently with ordering of the intermetallic core, followed by the layer-by-layer growth of a platinum shell via Ostwald ripening during the oxygen annealing treatment. Calculations based on density functional theory demonstrate that this process follows an energetically favourable path. These findings are expected to be useful for the future design of structured platinum alloy nanocatalysts.
Highlights
The catalytic performance of core-shell platinum alloy nanoparticles is typically superior to that of pure platinum nanoparticles for the oxygen reduction reaction in fuel cell cathodes
Crucial questions relating to core-shell formation exist as follows: (1) Can the whole Pt-M core-shell formation process be directly followed at the atomic scale in real time? (2) What drives the core-shell formation under the processing conditions? (3) Are there possibly new mechanisms that can be utilized to grow and tailor the Pt shell? To provide answers to these significant questions, here we investigate the core-shell formation process in Pt3Co NPs, by using our advanced in situ transmission electron microscopy technique at atmospheric gas pressure[17, 18]
An unexpected oxygen-driven core-shell formation process is observed at the atomic scale, and the corresponding mechanism is proposed based on our density functional theory (DFT) calculations
Summary
The catalytic performance of core-shell platinum alloy nanoparticles is typically superior to that of pure platinum nanoparticles for the oxygen reduction reaction in fuel cell cathodes. Calculations based on density functional theory demonstrate that this process follows an energetically favourable path These findings are expected to be useful for the future design of structured platinum alloy nanocatalysts. An unexpected oxygen-driven core-shell formation process is observed at the atomic scale, and the corresponding mechanism is proposed based on our density functional theory (DFT) calculations. These findings should help pave the way for the surface engineering and atomic-scale control of improved Pt-M core-shell nanocatalysts
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