Scientists uncover an easy approach to create atomically thin metal layers for new electronics.

The key to a perfect croissant is the number of layers, as many as possible, and the addition of butter to each one.In a similar vein, scientists are able to slip various ions between a number of extremely thin metal layers in a novel material that holds promise for novel applications. As a result, energy storage and high-tech electronics could benefit greatly from their use in the future.

These materials, which are pronounced “max-eens” and are referred to as MXenes, were previously as labor-intensive as good croissants made in a French bakery.

However, a new method developed by researchers at the University of Chicago demonstrates how to produce these MXenes in a much shorter amount of time and with fewer harmful byproducts.

“This is great if you’re making a few grams for laboratory investigations, but if you wanted to create huge volumes for commercial items, it would become a major corrosive waste disposal concern,”

 Dmitri Talapin, the Ernest DeWitt Burton Distinguished Service Professor of Chemistry at the University of Chicago,

The discovery, which was published on March 23 in the journal Science, is hoped to open the door for the use of MXenes in everyday electronics and devices and encourage new ideas.

Atom economy

When MXenes were discovered in 2011, their discovery excited many scientists. When metals like gold and titanium are shaved to create atomic-thin sheets, they typically cease to behave like metals. MXenes, on the other hand, have chemical bonds that are unusually strong, allowing them to retain metal’s special abilities, like strongly conducting electricity.

Furthermore, they are adaptable: Di Wang, a graduate student in chemistry, and Chenkun Zhou, a postdoctoral scholar, were the co-first authors of the paper. “You can use ions to store energy, for example,” they said.

MXenes could be used to build new devices that store electricity or block electromagnetic interference due to all of these advantages.

However, the only way we knew to make MXenes was to heat the mixture to 3,000°F and then immerse it in hydrofluoric acid for a few hours.

Dmitri Talapin, joint appointee at Argonne National Laboratory and corresponding author on the paper, explained, “This is fine if you’re making a few grams for experiments in the laboratory, but if you wanted to make large amounts to use in commercial products, it would become a major corrosive waste disposal issue.”  Talapin is the Ernest DeWitt Burton Distinguished Service Professor of Chemistry at the University of Chicago.

The team utilized chemistry principles, particularly “atom economy,” which aims to reduce the number of wasted atoms during a reaction, to create a method that was both more effective and less harmful.

MXenes can now be produced without the use of hydrofluoric acid thanks to new chemical reactions discovered by the University of Chicago team. Only one step is required: combining various chemicals and the metal you want to layer with and heating the mixture to 1,700°F. After that, you can open it, and there they are,” Wang stated.

Scientists can now develop and investigate novel varieties of MXenes for a variety of applications, including the production of various metal alloys and ion flavorings, thanks to the less complicated and toxic method. The method was tested with zirconium and titanium metals, but the team thinks it can be used with many other combinations.

Wang continued, “These new MXenes are also visually beautiful.”  Because the edges are exposed and accessible for ions and molecules to move in between the metal layers, they stand up like flowers, which may make them better for reactions.”

The paper also had Wooje Cho, a graduate student, as a co-author. X-ray research facility director Alexander Filatov, theoretical chemist Suri Vaikuntanathan, and electrochemists Chong Liu and Mingzhan Wang from the Pritzker School of Molecular Engineering all contributed to the success of the investigation. Electron microscopy was performed by Robert Klie and Francisco Lagunas of the University of Illinois at Chicago. 

More information: Di Wang et al, Direct synthesis and chemical vapor deposition of 2D carbide and nitride MXenes, Science (2023). DOI: 10.1126/science.add9204

Daniel D. Robertson et al, A direct and clean route to MXenes, Science (2023). DOI: 10.1126/science.ade9914

Topic : Article