Toward controllable and predictable synthesis of high-entropy alloy nanocrystals

Abstract

High-entropy alloy (HEA) nanocrystals have attracted extensive attention in catalysis. However, there are no effective strategies for synthesizing them in a controllable and predictable manner. With quinary HEA nanocrystals made of platinum-group metals as an example, we demonstrate that their structures with spatial compositions can be predicted by quantitatively knowing the reduction kinetics of metal precursors and entropy of mixing in the nanocrystals under dropwise addition of the mixing five–metal precursor solution. The time to reach a steady state for each precursor plays a pivotal role in determining the structures of HEA nanocrystals with homogeneous alloy and core-shell features. Compared to the commercial platinum/carbon and phase-separated counterparts, the dendritic HEA nanocrystals with a defect-rich surface show substantial enhancement in catalytic activity and durability toward both hydrogen evolution and oxidation. This quantitative study will lead to a paradigm shift in the design of HEA nanocrystals, pushing away from the trial-and-error approach.

Ternary NiMo-Bi liquid alloy catalyst for efficient hydrogen production from methane pyrolysis

“…S15). The different radial distances and coordination environment of Ni and Mo of NiMo-Bi catalysts, compared with metal foil counterparts, further proved that Ni and Mo were uniformly dispersed without any aggregation ( 36 ). Moreover, the difference between the Ni-Bi and NiMo-Bi catalysts indicated the interaction between Ni and Mo, which is also different from the traditional Ni-Bi alloy.…”

Intermetallic Nanocrystals for Fuel-Cells-Based Electrocatalysis

“…High-entropy alloys can be macroscopically defined as a novel material containing five or more dominant elemental components, of which the atomic percentage of constituent elements varying from 5% to 35%. − Due to the four-core effect, including high-entropy effect, lattice distortion effect, sluggish diffusion effect, and cocktail effect, high-entropy alloys have been widely applied in the field of biomedical materials, aerospace engineering, photothermal conversion, building materials, and magnetocaloric response, etc. − Especially, the continuous adjustment of the surface electronic structure on high-entropy alloys in nanoscale stimulates the development of heterogeneous catalysis. − High-entropy intermetallics, as a brand new concept, can integrate the advantages of high-entropy alloys and intermetallics, thus becoming an important supplement to high-entropy alloys and intermetallics and further enhancing the electrocatalytic activity and stability (Scheme a). − Although the ordered structure is an important feature of intermetallics different from disordered solid-solution alloys, the site occupancy in each sublattice of high-entropy intermetallics is still random or nearly random due to the more constituent elements than sublattices (Figure a).…”

Challenges and opportunities in 2D high‐entropy alloy electrocatalysts for sustainable energy conversion

“…The greater the degree of chaos, the higher the entropy. When the mixing entropy is between 1.2 R and 1.5 R , it is commonly classified as a medium entropy, while mixing entropy less than 1.2 R falls into the low entropy category 14,39,47,48 . The mixing entropy can be calculated using Equation (): $$$$\begin{equation}\Delta \;{S_{{\mathrm{mix}}}} = \; - R\left( {\mathop \sum \limits_{i\; = \;1}^n {x_i}\ln {x_{i}}} \right)\end{equation}$$$$where R is the gas constant (8.314 J [mol K] −1 ), x i is the mole fraction of each element in the alloy, and ln is the natural logarithm function.…”

“…Liu et al. have investigated the synthesis of HEAs with different morphologies by controlling the amount and rate of precursor addition 48 . Figure 2A illustrates that the mixing entropy rapidly increases and then decreases when all precursors are added simultaneously.…”

“…Reproduced with permission from ref. 48 Copyright 2023, CC BY‐NC. (C) The mixing entropy of the equi‐atomic ratio alloys as a function of the number to the components.…”