image: (a) Schematic of the arc-discharged approach for synthesizing different high-entropy-alloy nanoparticles. (b) XRD patterns of the high-entropy-alloy nanoparticles with different composited elements. (c) TEM-EDS maps of 21-elements nanoparticles, scale bar: 50 nm. view more
Credit: ©Science China Press
This study is led by Dr. Yixing Li (School of Materials Science and Engineering, Northeastern University) and Professor Xuefeng Zhang (School of Materials Science and Engineering, Northeastern University, & College of Materials and Environmental Engineering, Hangzhou Dianzi University). Multi-metallic nanoparticles, so-called high-entropy-alloy nanoparticles (HEA-NPs), are one of the most promising candidates for tailoring the optical absorption property. Such a performance is induced by the reinforced interband transitions, contributing from the fully filled energy regions around the Fermi level. However, Yixing Li and Xuefeng Zhang have found that the phase separation would occur when elements exceed eight, which could limit the exploration between the HEA-NPs and photothermal conversion performance.
Yixing Li and Xuefeng Zhang, together with PhD student Yijun Liao, summarized their recent preparations on the multi-metallic nanoparticles, and proposed a new idea for synthesizing such nanoparticles through the regulation of vapor pressure.
The synthesized process has been divided into three parts: extremely high evaporated temperature, ultra-fast cooling rate, and vapor pressure strategy. Based on the curves of vapor pressure, different composited metals used in this work have be divided into three groups: (i) metals with low vapor pressure, (ii) metals with medium vapor pressure; (iii) metals with high vapor pressure. Following this guideline, the 9-HEA-NPs of FeCoNiCrYTiVCuAl were synthesized from the mixture with a 10-time content of Ti and V and a 0.5-time content of Cu and Al. Using the 9-HEA-NPs as the substrate, a series of 13-, 17- and 21- HEA-NPs were synthesized. It can be concluded that the metals with low vapor pressure are the key to optimize the evaporation rate for alloying the immiscible combinations together. In addition, the crystalline structures were changed from face-centered-cubic (FCC) to body-centered-cubic (BCC) when the composited elements exceeded nine. (See below image).
The photothermal conversion properties of HEA-NPs show that the performance can be improved along with the addition of composited elements. In particular, the 21-elements nanoparticles exhibit an excellent solar steam generation performance with near 99% solar steam efficiency and 2.42 kg m-2 h-1 water evaporation rate under 1 sun irradiation.
The improvement of photothermal conversion performance mainly comes from two aspects: one is the strong absorption around the Fermi level from d-d Interband transitions, which is contributed by transition metal elements, the other is the reduction of thermal conductivity caused by lattice distortion effect, which is caused by the difference of atomic radius of constituent elements. The synergistic effect improves the photothermal conversion performance of 21-elements nanoparticles.
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See the article:
High-entropy-alloy nanoparticles with ultra-mixed 21 elements for efficient photothermal conversion
https://doi.org/10.1093/nsr/nwac041