Via conventional bimetallic synthesis methods, only readily miscible metals (shown in green) can mix with copper (Cu) while others (shown in red) form phase-segregated structures (such as core-shell). In contrast, via the novel non-equilibrium synthesis method, Cu and other metals can be kinetically trapped in homogeneously mixed nanoparticles, regardless of their thermodynamic miscibility. Image: Yang et al.
Via conventional bimetallic synthesis methods, only readily miscible metals (shown in green) can mix with copper (Cu) while others (shown in red) form phase-segregated structures (such as core-shell). In contrast, via the novel non-equilibrium synthesis method, Cu and other metals can be kinetically trapped in homogeneously mixed nanoparticles, regardless of their thermodynamic miscibility. Image: Yang et al.

The development of bimetallic nanoparticles – tiny particles composed of two different metals that exhibit several new and improved properties – represents a novel area of research with a wide range of potential applications. Now, a research team at the University of Maryland (UMD)'s A. James Clark School of Engineering has developed a new method for mixing metals generally known to be immiscible, or unmixable, at the nanoscale to create a new range of bimetallic materials. Such a library will be useful for studying the role of these bimetallic nanoparticles in various reaction scenarios, such as the transformation of carbon dioxide into fuel and chemicals.

"With this method, we can quickly develop different bimetallics using various elements but with the same structure and morphology," said Liangbing Hu, who led the research team. "Then we can use them to screen catalytic materials for a reaction; such materials will not be limited by synthesizing difficulties." Hu and his team report their work in a paper in Science Advances.

The complex nature of nanostructured bimetallic particles makes synthesizing such particles difficult using conventional methods, for a variety of reasons – including the chemical makeup of the metals, the particle size and how metals arrange themselves at the nanoscale.

This new non-equilibrium synthesis method works by exposing copper-based mixes to a thermal shock of approximately 1300°C for .02 seconds and then rapidly cools them to room temperature. The reason for using such a short interval of thermal heat is to quickly trap, or 'freeze', the high-temperature metal atoms at room temperature while maintaining their mixing state. In doing so, the research team was able to prepare a collection of homogeneous copper-based alloys.

Typically, copper only mixes with a few other metals, such as zinc and palladium. But with this new method, the team were able to broaden the miscible range to include copper with nickel, iron and silver as well.

"Using a scanning electron microscope and transmission electron microscope, we were able to confirm the morphology – how the materials formed – and size of the resulting Cu-Ag [copper-silver] bimetallic nanoparticles," said Chunpeng Yang, a research associate and first author of the paper.

This novel method will allow scientists to create more diverse nanoparticle systems, structures and materials for use in catalytical, biological, optical and magnetic applications.

As a model system for rapid catalyst development, the team investigated copper-based alloys as catalysts for carbon monoxide reduction (COR) reactions, in collaboration with Feng Jiao, a professor at the University of Delaware. The electro-catalysis of COR reactions is an attractive platform, offering a way for scientists to use greenhouse gases and renewable electrical energy to produce fuels and chemicals.

"Copper is, thus far, the most promising monometallic electrocatalyst that drives carbon monoxide reduction to value-added chemicals," said Jiao. "The ability to rapidly synthesize a wide variety of copper-based bimetallic nanoalloys with a uniform structure enables us to conduct fundamental studies on the structure-property relationship in COR and other catalyst systems."

The non-equilibrium synthetic strategy can also be extended to other bimetallic or metal oxide systems. Utilizing artificial intelligence-based machine learning, this new synthetic method will make rapid catalyst screening and rational design possible.

This story is adapted from material from the University of Maryland, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.