Issue 20, 2022

The delicate balance of phase speciation in bimetallic nickel cobalt nanoparticles

Abstract

Bimetallic nickel–cobalt nanoparticles are highly sought for their potential as catalytic and magnetic nanoparticles. These are typically prepared in organic solvents in the presence of strong stabilizing ligands such as tri-n-octylphosphine (TOP). Due to the variety of cobalt crystallographic phases and to the strong interaction of the ligands with the metallic surfaces, forming fcc nanoparticles rather than a phase mixture is a challenging endeavor. Here, using a two-step synthesis strategy that aims at a core–shell nickel–cobalt morphology, we demonstrated that many parameters have to be adjusted: concentration of the metal precursors, stoichiometry of TOP, and heating program from room temperature to 180 °C. We found optimized conditions to form size-controlled fcc NiCo nanoparticles from preformed Ni nanoparticles, and the phase attribution was confirmed with a combination of X-Ray diffraction on powder and X-Ray absorption spectroscopy at the Co K edge. We then investigated the early stages of Co nucleation on the nickel using a lower stoichiometry of Co, down to 0.05 equiv. vs. Ni. Using X-ray photoelectron spectroscopy and scanning transmission electron microscopy coupled to energy-dispersive X-Ray spectroscopy and electron energy loss spectroscopy, we showed that cobalt reacts first on the nickel nanoparticles but easily forms cobalt-rich larger aggregates in the further steps of the reaction.

Graphical abstract: The delicate balance of phase speciation in bimetallic nickel cobalt nanoparticles

Supplementary files

Article information

Article type
Paper
Submitted
16 Febr. 2022
Accepted
04 Apr. 2022
First published
04 Apr. 2022

Nanoscale, 2022,14, 7547-7560

The delicate balance of phase speciation in bimetallic nickel cobalt nanoparticles

A. Palazzolo, C. Poucin, A. P. Freitas, A. Ropp, C. Bouillet, O. Ersen and S. Carenco, Nanoscale, 2022, 14, 7547 DOI: 10.1039/D2NR00917J

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