2021
_FEATURE

The Ever-Expanding Applications of MXenes
A decade after Drexel researchers invented a tiny 2D material called MXene, its potential for engineering novel materials and applications has only increased — even in a pandemic.

_Michel Barsoum

Barsoum is a distinguished professor in the College of Engineering.

_Yury Gogotsi

Gogotsi is a Distinguished University and Charles T. and Ruth M. Bach Professor of Materials Science and Engineering and director of the A.J. Drexel Nanomaterials Institute in the College of Engineering.

In 2011, researchers in Drexel’s Department of Materials Science and Engineering discovered an atoms-thin, two-dimensional material that has since transformed the field of 2D materials and, potentially, may change the way we live and use technology.

The material, dubbed MXene — pronounced “Maxine” and named for its chemical shorthand (“M” for metal, like titanium, and “X” for carbon and/or nitrogen) — was discovered by Drexel’s Distinguished Professor Michel Barsoum and Distinguished University and Charles T. and Ruth M. Bach Professor Yury Gogotsi. A decade ago, they were working on a Department of Energy (DoE) grant to make electrode materials for batteries, and created something unique when they added hydrofluoric acid to MAX phases, which are highly conductive layered materials with ceramic and metal properties that Barsoum developed in the late ’90s.

Since then, their research teams have created and/or discovered several dozen different types of MXenes (depending on the type of MAX phase and etchant) and have studied the different properties of many of those new materials.

These MXenes remain highly conductive when applied in a variety of forms (everything from spray-paint to ink). This versatile and groundbreaking attribute solved the problem they were working on (improving energy storage), but also opened a whole world of possibilities to explore and answer. With MXenes, electronics could be made both smaller and faster; batteries could be made more long-lasting; wearable technology could become an everyday habit; pure hydrogen could be produced in a more efficient and cost-effective way; sensors detecting chemicals in the air could be improved; and a wearable kidney could be made to replace immobile, time-consuming kidney dialysis machines, among many other possibilities.

01 Blocking Interference

Titanium carbonitride, part of the MXene family, has the ability to both block and absorb electromagnetic interference (EMI) better than any known material — even the metal foils currently used in most electronic devices. You’ve probably noticed EMI as the annoying buzzing noise from a microphone or speaker, but EMI is a serious concern due to its ability to diminish electrical performance, slow data exchange rates and even interrupt the function of devices. EMI can be contained and deflected by covering the entire circuit board with a copper cage or by wrapping individual components in foil shielding, but researchers at Drexel and the Korea Institute of Science and Technology found that titanium carbonitride is just as effective, and thinner and lighter too.

“This discovery breaks all the barriers that existed in the electromagnetic shielding field. It not only reveals a synthetic inorganic shielding material that works better than copper, but it also shows an exciting, new physics emerging, as we see discrete 2D materials interact with electromagnetic radiation in a different way than bulk metals,” says Gogotsi.

Moreover, Gogotsi’s group has known that MXenes not only have the ability to block electromagnetic interference better than other materials, but also effectively adhere to fabrics and maintain their unique shielding capabilities when incorporated into textiles. As a result, titanium carbide–coated fabric can protect people and their gadgets from microwave radiation.

02 No Water, No Problem

“Water has been used in the MXene-making processes to dilute the etching acid and as a solvent to neutralize the reaction, but it is not always desirable to have traces of it in the finished product,” says Barsoum. “We have been working for some time to explore other etchants for the MAX phases and now we have found just the right combination of chemicals to do it.”

Barsoum and other Drexel researchers found a way to remove water from the MXene-making process, making the 2D materials ideal for creating battery electrodes, next-generation solar cells and other applications where the presence of water could degrade performance.

In the past, MXenes were produced by using a concentrated acid to carve away atomic layers from a MAX phase material, then washing that out with water to create flakes of the 2D-layered material. Now, a solution made of organic solvent and ammonium dihydrogen fluoride — a chemical commonly used to etch glass — does the same, but without water to dilute it or to wash away the by-products. So not only can MXenes be used for applications that could be hindered by any added water, but it can be added to materials that would degrade in water.

03 Making More MXene

Only a handful of 2D materials have the potential to be produced in industrial-size quantities — and now, MXenes are one of them. Drexel researchers working with the Materials Research Center in Ukraine developed a way to make MXenes in batches large enough to be considered viable for manufacturing, while still preserving the material’s unique properties.

This is hugely attractive for companies wanting to develop applications of MXene materials, and reaching manufacturing standards is one item to be checked off the “to-do” list for mainstream use of MXene.

“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,” explains Gogotsi. “This means that MXene can be considered for widespread use in electronics and energy-storage devices.”

04 See the Light 

Photodetectors convert information carried by light into an electric signal that can be processed by electronic circuits and computers — a useful application for everyday devices like television remotes, and one that has unlimited potential in sensing, artificial intelligence, Internet of Things (IoT), and optical data storage.

It’s no wonder, then, that the photodetector is such a high-demand product, but it’s also a costly one. Expensive materials like gold and titanium are needed to fabricate them in highly controlled conditions produced by capital-intensive equipment. Drexel researchers found that replacing gold with a translucently thin layer of MXene material can scale up the photodetector production process and churn out sensors that are superior (and less costly) compared to the, ahem, gold standard.

05 Ready for 5G

Drexel researchers created new antennas made of MXenes that are thin enough to spray-on, but also strong enough to send a signal at bandwidths that will be used by fifth-generation (5G) mobile devices. This has promising potential for the future of telecommunications and 5G technology, but also shows that MXenes can be spray applied, screen printed or inkjet-printed onto just about any substrate and remain flexible without sacrificing performance.

“This combination of communications performance with extreme thinness, flexibility and durability sets a new standard for antenna technology,” says Gogotsi. “While copper antennas have been the best in terms of performance for quite some time, their physical limitations have prevented connected and mobile technology from making the big leaps forward that many have predicted. Due to their unique set of characteristics MXene antennas could play an enabling role in the development of IoT technology.”

06 MXene as Catalysts

“Efficient catalysts are crucial for reducing energy consumption in the manufacturing of many chemical reagents and for the electrolytic production of hydrogen from water,” Barsoum says, and MXene and its composites can be used as promising catalysts in different reactions. 

Drexel and French researchers reacted MXene powders with sulphur to form a catalyst for hydrogen evolution that’s almost as good as carbon-platinum, one of the best-known catalysts for this reaction.

Researchers around the world are now studying this family of materials and hundreds of international and U.S. patent applications have been filed. Drexel’s MXene patent portfolio now includes 12 issued U.S. patents and two dozen invention disclosures received across the United States, Europe and Asia, covering core MXene composition of matter, formulations, methods of manufacture and various applications and systems. An additional 36 patent prosecutions (including provisional patent applications) are ongoing, and there are five licenses for exclusive commercial fields of use (electronics and biomedical applications) or for R&D distribution with materials suppliers. Currently, the University is working with several dozen companies to evaluate other MXene applications.

“It is very exciting to see MXenes take the world by storm,” Barsoum reflects. “The science behind them is fascinating and will more likely than not lead to some major breakthroughs. This is especially true given the extraordinary number of potential applications being explored — from energy storage to curing cancer to electromagnetic interference shielding, among many more.”

In 2020, MXene research and scholarship continued despite the COVID-19 pandemic, and a planned international conference in August transformed into an even bigger and more open virtual conference. Barsoum and Gogotsi organized and chaired the “MXenes 2020” three-day event that remotely brought together about 2,500 registered participants from more than 60 countries, which was preceded by a week-long course on synthesis and characterization of MXenes for about 60 students from around the world. Gogotsi plans to offer this course again in 2021 to American and international audiences.

And this year, as in years prior, Gogotsi, Barsoum and other Drexel researchers worked on a variety of MXene research projects that are expanding the field of MXene applications. Following are just a few examples.