Continuous-Flow Reactor Synthesis for Homogeneous 1 nm-Sized Extremely Small High-Entropy Alloy Nanoparticles

Abstract

High-entropy alloy nanoparticles (HEA NPs) emerged as catalysts with superior performances that are not shown in monometallic catalysts. Although many kinds of synthesis techniques of HEA NPs have been developed recently, synthesizing HEA NPs with ultrasmall particle size and narrow size distribution remains challenging because most of the reported synthesis methods require high temperatures that accelerate particle growth. This work provides a new methodology for the fabrication of ultrasmall and homogeneous HEA NPs using a continuous-flow reactor with a liquid-phase reduction method. We successfully synthesized ultrasmall IrPdPtRhRu HEA NPs (1.32 ± 0.41 nm), theoretically each consisting of approximately 50 atoms. This average size is the smallest ever reported for HEA NPs. All five elements are homogeneously mixed at the atomic level in each particle. The obtained HEA NPs marked a significantly high hydrogen evolution reaction (HER) activity with a very small 6 mV overpotential at 10 mA/cm–2 in acid, which is one-third of the overpotential of commercial Pt/C. In addition, although mass production of HEA NPs is still difficult, this flow synthesis can provide high productivity with high reproducibility, which is more energy efficient and suitable for mass production. Therefore, this study reports the 1 nm-sized HEA NPs with remarkably high HER activity and establishes a platform for the production of ultrasmall and homogeneous HEA NPs.

Quinary, Senary, and Septenary High Entropy Alloy Nanoparticle Catalysts from Core@Shell Nanoparticles and the Significance of Intraparticle Heterogeneity

“…Then, in 2018, Yao et al reported discrete HEA nanoparticles (NPs) . These demonstrations inspire study of synthetic pathways to nanostructured HEAs as their complex compositions and crystal size effects may together bring distinct functionality. ,,− …”

Chemical Synthesis, Characterization, and Properties of Multi‐Element Nanoparticles

“…Reprinted with permission from ref. [70] Copyright 2022, American Chemical Society. (NM-HEA NPs, Figure 5c, d).…”

Chemical Synthesis, Characterization, and Properties of Multi‐Element Nanoparticles

“…[69] Copyright 2021, American Chemical Society) and d) carbon as support (PVP-free) (equipment in Figure 6c, d) (adapted with permission from ref. [70] Copyright 2022, American Chemical Society). Reprinted with permission from ref.…”

“…[77][78][79][80][81][82] With the development of various types of flow reactors, alloy NPs with different compositions and structures have been reported in the last five years. [69,70] Kusada et al synthesized the first example of HEA NPs by using a home-designed flow reactor. [69] Inspired by the hot-injection methods employed in the batch synthesis, the researchers designed the reactor to be able to realize the concurrent supply of the constituent atoms during the nucleation and particle growth processes.…”

“…Quite recently, Minamihara and coauthors developed a desktop-type flow reactor capable of synthesizing ultrasmall HEA NPs. [70] The flow reactor has two diaphragm pumps with smooth pulsation to supply Solution 1 (mixture of acetylacetonate salts of Ir, Pd, Pt, Rh, and Ru dissolved in deoxidized tetrahydrofuran [THF]) and Solution 2 (lithium naphthalenide in THF) separately (Figure 6c, d). The two solvents were deoxygenated and the reaction proceeded under Ar.…”