Breaking with the Principles of Coreduction to Form Stoichiometric Intermetallic PdCu Nanoparticles

Abstract

surface sites. Each metal has a specific binding affinity toward the adsorbates involved in each catalytic reaction, which allows for selective tuning and optimization of catalytic processes via consideration of the incorporated metals. [1] In a binary disordered alloy, two metals randomly occupy symmetry equivalent sites in the crystal lattice, while the metals in an intermetallic structure occupy the crystallographic sites in the structure in a nonrandom arrangement at a specific atomic stoichiometry. [2] Alloys and intermetallics are known to have very different properties for catalysis. For example, intermetallic NPs composed of Pd and Cu have been observed to display superior catalytic activities in the CO 2 reduction reaction and oxygen reduction reaction over disordered face-centered cubic (fcc) alloys of the same composition, which has been attributed to changes in the electronic surface structure owing to the differences in local atomic arrangements. [3,4] In order to explore and implement the improved catalytic properties accessible in intermetallic NPs, it is crucial that the NP structure is controlled to promote only the most catalytically active structure. This degree of control can be obtained only if we understand how intermetallic NPs are formed, and which synthetic conditions dictate the resulting structure. Previous studies have indicated that the formation of intermetallic PdCu NPs proceeds through a disorder-order transformation, Intermetallic nanoparticles (NPs) have shown enhanced catalytic properties as compared to their disordered alloy counterparts. To advance their use in green energy, it is crucial to understand what controls the formation of intermetallic NPs over alloy structures. By carefully selecting the additives used in NP synthesis, it is here shown that monodisperse, intermetallic PdCuNPs can be synthesized in a controllable manner. Introducing the additives iron(III) chloride and ascorbic acid, both morphological and structural control can be achieved. Combined, these additives provide a synergetic effect resulting in precursor reduction and defect-free growth; ultimately leading to monodisperse, single-crystalline, intermetallic PdCu NPs. Using in situ X-ray total scattering, a hitherto unknown transformation pathway is reported that diverges from the commonly reported coreduction disorder-order transformation. A Cu-rich structure initially forms, which upon the incorporation of Pd(0) and atomic ordering forms intermetallic PdCu NPs. These findings underpin that formation of stoichiometric intermetallic NPs is not limited by standard reduction potential matching and coreduction mechanisms, but is instead driven by changes in the local chemistry. Ultimately, using the local chemistry as a handle to tune the NP structure might open new opportunities to expand the library of intermetallic NPs by exploiting synthesis by design.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smtd.202200420.

Intermetallic Nanocrystals for Fuel-Cells-Based Electrocatalysis

“…In addition, an oleylamine reaction system consisting of metal acetylacetonates, FeCl 3 , and AA was used for directly synthesizing ordered PdCu intermetallic nanoparticles . The growth mechanism of PdCu intermetallics under such synthesis conditions was further clarified using in situ X-ray total scattering and pair distribution function analysis . They found that the successful synthesis required both additives capable of reoxidation of Fe 3+ ↔ Fe 2+ and fast and continuous reducing agents.…”

“…286 The growth mechanism of PdCu intermetallics under such synthesis conditions was further clarified using in situ X-ray total scattering and pair distribution function analysis. 287 They found that the successful synthesis required both additives capable of reoxidation of Fe 3+ ↔ Fe 2+ and fast and continuous reducing agents. Specifically, Fe 3+ was first reduced into Fe 2+ to oxidatively etch preformed Cu-rich seeds to form metal ions (M + ), and then the AA was oxidized into dehydroascorbic acid to dampen the reduction rate of metal ions.…”

Formation of intermetallic PdIn nanoparticles: influence of surfactants on nanoparticle atomic structure

“…Metal halides are commonly used for synthesis of bi-and intermetallic NPs. 17,28 Firstly, it is well-known that halide ions (e.g. Cl − , Br − ) can modify reduction kinetics and the atom diffusion/ exchange rate by coordinating with metal ions during the synthesis of metallic NPs.…”

“…The reaction does thus not take place through the conventional Bain transformation, which we have previously observed for PdCu. 17 Instead, the PdIn particles may…”

A reactor for time-resolved X-ray studies of nucleation and growth during solvothermal synthesis

“…Other reactors exist, as reviewed by Jensen et al (2014), and the various reactors have different strengths including probing at the mixing point of a mixing-flow reactor (Beauvais et al, 2022). Alternative approaches include employing nuclear magnetic resonance tubes with a larger diameter of 3 mm, such as in a recent study of PdCu 3 formation (Mathiesen et al, 2022).…”