Manufacturing Bits: March 17

Making MXenes
Drexel University and the Materials Research Center in the Ukraine have devised a system for use in making large quantities of MXenes, a promising set of materials used for energy storage and related applications.

A class of two-dimensional inorganic compounds, MXenes consist of thin atomic layers. The materials are based on transition metal carbides, nitrides or carbonitrides.

MXenes are durable and conductive materials. They could one day improve energy storage systems. Other applications include computing, communications and health care.

In 2011, Drexel began making MXenes in small quantities. The typical production quantity is one gram or less. The material, which resembles a powder, starts with a piece of ceramic.

Then, the material is mixed with hydrofluoric and hydrochloric acid. This in turn etches away parts of the material, creating thin flakes of MXenes.

Researchers have developed a new process. They can convert a ceramic precursor material into a MXene titanium carbide–in quantities as large as 50 grams per batch.

A reactor and other systems were able to make just under 50 grams of MXene powder from 50 grams of a MAX phase precursor material in two days, according to researchers.

The resulting MXene material retains its morphology, electrochemical and physical properties. “And with the process that we’ve developed, we can stamp or print tens of thousands of small and thin devices, such as supercapacitors or RFID tags, from material made in one batch,” said Yury Gogotsi, a professor in Drexel’s College of Engineering.

“Proving a material has certain properties is one thing, but proving that it can overcome the practical challenges of manufacturing is an entirely different hurdle — this study reports on an important step in this direction. This means that MXene can be considered for widespread use in electronics and energy storage devices,” Gogotsi said.

“It typically takes quite a while to build out the technology and processing to get nanomaterials in an industrially usable form,” Gogotsi said. “It’s not just a matter of producing them in large quantities; it often requires inventing completely new machinery and processes to get them in a form that can be inserted into the manufacturing process — of a microchip or cell phone component, for example.”

Macroscopic MXenes
The Institute of Solid State Physics (ISSP) within the Hefei Institutes of Physical Science has developed a macroscopic MXene using a wet-chemical method.

Generally, the dimensions of a MXene is at the micron level or smaller. They are produced by etching polycrystalline powders at the micron level. But this limits the applications for the materials.

To solve the problem, ISSP grew millimeter-scale V4AlC3 single crystals. This was done using a high-temperature flux method. The crystals were immersed in hydrofluoric acid at room temperature for 40 days. The crystals were selectively etched. This in turn resulted in a macro-sized MXene.

This could pave the way for MXenes in electronic and photonic devices.