Ensemble versus Local Restructuring of Core‐shell Nickel–Cobalt Nanoparticles upon Oxidation and Reduction Cycles

Abstract

Bimetallic nanoparticles are widely studied, for example in catalysis. However, possible restructuring in the environment of use, such as segregation or alloying, may occur. Taken individually, state-of-the-art analytical tools fail to give an overall picture of these transformations. This study combines an ensemble analysis (near-ambient-pressure X-ray photoelectron spectroscopy) with a local analysis (environmental transmission electron microscopy) to provide an in situ description of the restructuring of core-shell nickel-cobalt nanoparticles exposed to cycles of reduction and oxidation. It reveals a partial surface alloying accompanied by fragmentation of the shell into smaller clusters, which is not reversible. Beyond this case study, the methodology proposed here should be applicable in a broad range of studies dealing with the reactivity of mono- or bi-metallic metal nanoparticles.

Influence of the Cobalt Active Site Neighbours in NiCo Nanocatalysts for Phosphine‐Assisted Silane Activation

“…[35] The oxidized species observed for Ni (light green), Co (light red) and P (light blue), were expected as they were possibly formed during the synthesis and/or as the result of the washing in air. However the presence of these species was not an issue for the catalytic reaction: since it was conducted in reducing conditions, it is expected that the surface state presents less oxidized species, as evidenced previously by near-ambient pressure XPS on NiCo NPs [33] and in agreement with our recent work. [28] Moreover, the presence of reduced P species of phosphide type suggested that some P was incorporated in the metallic surface, a phenomenon previously observed on NiCo nanoparticles.…”

“…It confirmed the formation of an oxidized layer on the surface of the nanoparticles. The spectra were analyzed with CasaXPS following the methodology of our previous works [30,[32][33][34][35] and fitting parameters can be found in the SI. The Ni 2p region (Figure 2C) was fitted with two components: [36] metallic nickel at a binding energy (B.E.)…”

Highly Efficient Dynamic Degradation of Methylene Blue on Hierarchical Nitrogen/Cobalt‐Co‐Doped Carbonaceous Beads with Diffusion Promoting Nanostructures

“…Thus, it can better encapsulate and protect the nanoparticles. [25] Additionally, TEM of SA/NÀ Co x O y was also detected, and the results are displayed in Figure 2(e) and Figure 2(f). Obviously, all the nanoparticles were quite uniformly dispersed in hydrogel beads interior without aggregation and agglomeration, which is in consistent with the outcomes of SEM.…”

“…Some hexagonal expanded pores and silk texture were emerged, which further result in the enhancement in surface area and pore structure. Thus, it can better encapsulate and protect the nanoparticles …”