General Solvothermal Synthesis Method for Complete Solubility Range Bimetallic and High‐Entropy Alloy Nanocatalysts

Abstract

Nanoalloys (NAs) have extraordinary catalytic properties, but metals are often immiscible giving compositional limits on catalytic design. It is generally believed that solution‐based chemical synthesis is inadequate for obtaining NAs, and often exotic shock synthesis or severe decomposition or reduction reactions are required. However, such methods only work on the laboratory scale making real‐world applications difficult. Here, a general solvothermal method is reported to obtain phase‐pure bimetallic and high‐entropy nano‐alloys across the entire composition range. Tuning of solvent chemistry and precursors leads to six different bimetallic NAs: PdxRu1‐x, PtxRu1‐x, IrxRu1‐x, RhxRu1‐x, Ir1‐xPtx, and Rh1‐xPtx, without immiscibility regions. All samples have face‐centered‐cubic crystal structures, which have not previously been observed for the ruthenium‐based systems. Additionally, quaternary and quinary systems are produced, demonstrating the ability to obtain medium‐ and high‐entropy NAs. The method described herein provides a simple, general production method of previously unknown solid solutions throughout their entire composition range potentially allowing for detailed tuning of nanocatalyst properties.

Autocatalytic Formation of High‐Entropy Alloy Nanoparticles

“…Magnetron sputtering has been utilized for obtaining HEA thin films or nanoparticles, either using multiple targets in a co‐sputtering process or a single target composed of pressed metal powders [8b, 19] . Recently, a general environmentally benign, simple and scalable solvothermal autoclave process was developed for HEA nanoparticles using reaction temperatures as low as 200 °C [20] . Formation of HEAs from metal salt precursors necessarily involves reduction of the metals, and it is intriguing that acetylacetonate precursors of five widely different metals such as Pt, Ir, Pd, Rh and Ru can be simultaneously reduced and merged into a homogenous nanoparticle.…”

Nano High‐Entropy Materials: Synthesis Strategies and Catalytic Applications

“…A series of noble metal acetylacetonate dissolved in an acetone–ethanol solvent went through a solvothermal process at 200 °C for 4–24 h, which provides careful control of the reduction kinetics for the noble metal precursors. [ 52 ] However, it is difficult to apply this fabrication method to various high‐entropy systems due to the differences in reduction kinetics of diverse metal precursors. Taking advantage of the acoustic cavitation phenomenon in ultrasonication process, Dai and coworkers synthesized PtAuPdRhRu HEA‐NPs with ethylene glycol as reductant and solvent through an ultrasonication‐assisted wet chemistry method.…”

The Synthesis and Catalytic Applications of Nanosized High‐Entropy Alloys

“…Bondesgaard et al . prepared nanoalloys by tuning metal precursor species and solvent properties [24] . The choice of metal precursor has a great influence on the synthetic process as the different pre‐nucleation structure leaded to different reaction pathways.…”

“…In 2018, the seminal research on carbothermal shock synthesis of carbon supported HEA nanoparticles (NPs) triggered the pursuit of creative approaches for downsizing HEAs to the nanoscale regime [21] . Since then, various methods, such as fast pyrolysis, solvothermal synthesis and mechanical alloying, have been developed [22–25] . With the advancement of synthesis techniques, progress has hinged on the applications of available HEA−NPs in new research areas [26–30] …”