[SEMINAR] Precise Control of Three-Dimensional Atomic Arrangement in Nanoparticles: Phase Control and High-entropy Alloying

Title: Precise Control of Three-Dimensional Atomic Arrangement in Nanoparticles: Phase Control and High-entropy Alloying

Speaker: Kohei Kusada

From: Kyoto University 

Abstract: Inorganic nanoparticles (NPs) such as metal NPs synthesized in a liquid phase usually have a three-dimensional atomic arrangement same as their bulk forms. For example, NPs of a metal element with a hexagonal close-packed (hcp) structure in bulk have the hcp structure, and alloy NPs have a phase-separated structure with an immiscible alloy system. This is because the NPs with an equilibrium phase are formed through the self-assembly of atoms during chemical reduction synthesis. Therefore, it is common that we can select elements as we like when we design metal NPs, but we cannot easily control their crystal structures. Properties of metal NPs such as catalytic properties are significantly influenced by their electronic structure and surface structure. Therefore, if we could control the crystal structure of materials regardless of elemental species, we would be able to obtain a new direction to design functional nanomaterials since the electronic structure and atomic arrangement of the surface depend on the crystal structure. In this presentation, some examples of phase-controlled metal NPs and high-entropy (HE) nanomaterials with their catalytic properties will be introduced. We have successfully controlled crystal structures of monometallic and alloy NPs by utilizing their surface energy or precisely tuning the reduction speeds of precursors during the reactions.[1-3] As an example, we succeeded in selectively synthesizing fcc and hcp RuIrPt ternary alloys at a certain composition and found that the hcp one had higher catalytic activity for electrochemical hydrogen evolution reaction.[3]

Also, NPs containing multi-elements in a single phase, in particular, alloys containing more than five elements at almost equal ratios called high-entropy alloys (HEAs), have recently attracted much attention as new types of nanomaterials such as catalysts. We synthesized new HEA NPs and studied their catalytic properties based on their electronic structures.[4-9] Furthermore, perovskite-type denary HE oxide NPs were obtained by supercritical water flow synthesis.[10] The HEA has high durability and high electrochemical activity for hydrogen evolution reaction and alcohol oxidation reactions. The perovskite-type HEO showed higher catalytic activity of CO oxidation than LaFeO₃ NPs.

References

[1] JACS., 2013, 135, 5493-5496. [2] Nature Commun., 2018, 9, 510 [3] JACS, 2022, 144, 4224–4232. [4] JACS, 2020, 142, 13833–13838. [5] JACS, 2022, 144, 3365–336. [6] Chem. Sci., 2020, 11, 12731–12736. [7] J. Phys. Chem. C, 2021, 125, 458–463. [8] JACS, 2022, 144, 11525–11529. [9] JACS, 2023, 145, 17136–17142. [10] JACS, 2024, 146, 181–186.