The scientists whose job it is to test the limits of what nature—specifically chemistry— will allow to exist, just set up shop on some new real estate on the Periodic Table.
Using a method they invented for joining disparate elemental layers into a stable material with uniform, predictable properties, Drexel University researchers are testing an array of new combinations that may vastly expand the options available to create faster, smaller, more efficient energy storage, advanced electronics and wear-resistant materials.
Led by postdoctoral researcher Babak Anasori, PhD, a team from Drexel’s Department of Materials Science and Engineering created the material-making method, that can sandwich 2-D sheets of elements that otherwise couldn’t be combined in a stable way. And they proved its effectiveness by creating two entirely new, layered two-dimensional materials using molybdenum, titanium and carbon.
“By ‘sandwiching’ one or two atomic layers of a transition metal like titanium, between monoatomic layers of another metal, such as molybdenum, with carbon atoms holding them together, we discovered that a stable material can be produced,” Anasori said. “It was impossible to produce a 2-D material having just three or four molybdenum layers in such structures, but because we added the extra layer of titanium as a connector, we were able to synthesize them.”
The discovery, which was recently published in the journal ACS Nano, is significant because it represents a new way of combining elemental materials to form the building blocks of energy storage technology—such as batteries, capacitors and supercapacitors, as well as superstrong composites—like the ones used in phone cases and body armor. Each new combination of atom-thick layers presents new properties and researchers suspect that one, or more, of these new materials will exhibit energy storage and durability properties so disproportional to its size that it could revolutionize technology in the future.
“While it’s hard to say, at this point, exactly what will become of these new families of 2-D materials we’ve discovered, it is safe to say that this discovery enables the field of materials science and nanotechnology to move into an uncharted territory,” Anasori said.
Combining two-dimensional sheets of elements in an organized way to produce new materials has been the goal of Drexel nanomaterials researchers for more than a decade. Imposing this sort of organization at the atomic level is no easy task.
“Due to their structure and electric charge, certain elements just don’t ‘like’ to be combined,” Anasori said. “It’s like trying to stack magnets with the poles facing the same direction—you’re not going to be very successful and you’re going to be picking up a lot of flying magnets.”
But Drexel researchers came up with a clever way to circumvent this chemistry challenge. It starts with a material called a MAX phase, which was discovered by Distinguished Professor Michel W. Barsoum, PhD, head of the MAX/MXene Research Group, more than two decades ago. A MAX phase is like the primordial ooze that generated the first organisms—all the elements of the finished product are in the MAX phase, waiting for the researchers to impose some order.
That order was imposed by Michel W. Barsoum, PhD and Yury Gogotsi, PhD, Distinguished University and Trustee Chair professor in the College of Engineering and head of the Drexel Nanomaterials Group, when they first created a stable, two-dimensional, layered material called MXene in 2011.
To create MXenes, the researchers selectively extract layers of aluminum atoms from a block of MAX phase by etching them out with an acid.
“Think of MXene synthesis like separating layers of wood by dunking a plywood sheet into a chemical that dissolves the glue,” Anasori said. “By putting a MAX phase in acid, we have been able to selectively etch away certain layers and turn the MAX phase into many thin 2-D sheets, which we call MXenes.”
As far as energy storage materials go, MXenes were a revelation. Prior to their discovery, graphene, which is a single sheet of carbon atoms, was the first two-dimensional material to be touted for its potential energy storage capabilities. But, as it was made up of only one element, carbon, graphene was difficult to modify in form and therefore had limited energy storage capabilities. The new MXenes have surfaces that can store more energy.
An Elemental Impasse
Four years later, the researchers have worked their way through the section of the Periodic Table with elements called “transition metals,” producing MAX phases and etching them into MXenes of various compositions all the while testing their energy storage properties.
Anasori’s discovery comes at a time when the group has encountered an obstacle on its progress through the table of elements.
“We had reached a bit of an impasse, when trying to produce a molybdenum containing MXenes,” Anasori said. “By adding titanium to the mix we managed to make an ordered molybdenum MAX phase, where the titanium atoms are in center and the molybdenum on the outside.
The Next Frontier
Now, with the help of theoretical calculations done by researchers at the FIRST Energy Frontier Research Center at the Oak Ridge National Laboratory, Drexel’s team knows that, in principle, it can use this method to make as many as 25 new materials with combinations of transition metals, such as molybdenum and titanium, that previously wouldn’t have been attempted.
The Latest on: Layered MXene
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The Latest on: Layered MXene
- 3D-printing customized MXene architectureson August 5, 2019 at 11:57 pm
Formulating 3D-printable MXene inks and integrating them into customized 3D device architectures would provide a high degree of architectural control, scalability, and cost-effectiveness. However, ...
- Finding a needle in a haystack: Discovery of Ti 2 InB 2 for synthesizing layered TiBon May 31, 2019 at 8:26 am
Because direct synthesis of layered TiB is impossible ... the researchers believe that it will be possible to obtain TiB MXene in the future. Thus, they carried out a number of calculations ...
- What are MXenes?on April 3, 2019 at 9:28 am
MXenes are created by selectively removing aluminum from layered MAX phases. Through this exfoliation process, the carbide layers are separated into two MXene sheets just a few atoms thick. MXenes can ...
- Silicon Anodes May Improve Lithium Ion Batterieson February 26, 2019 at 4:38 am
It’s the MXene framework that also imposes order on ions as they arrive and prevents the anode from expanding.” MXenes were first discovered at Drexel in 2011. They are made by chemically etching a ...
- Semi-transparent EMI coating is flexible and quick to applyon November 2, 2018 at 8:28 am
Their physical characteristics mean that the alternating layers bond strongly together, and both types of layer, particularly the MXene, are electrically conductive. By altering the number of layers ...
- Strong, flexible films that allow light in but keep electromagnetic interference outon November 2, 2018 at 3:21 am
then dipped again in another layer, and so on and so on. That takes days. Our system can create hundreds of bi-layers of alternating MXene and CNT – in minutes." While spin-spraying limits component ...
- Cannibalistic Materials Eyed for New Fast-Charging Electronicson October 5, 2018 at 2:29 am
the suspended flake was exposed to heat and irradiated with an electron beam to clean the MXene surface and fully expose the layer of titanium atoms, researchers said. Typically inert materials, ...
- Are Spray-On Antennas the Future of Wearables?on September 26, 2018 at 6:18 am
MXene powder can be dissolved in water to create a paint that is then airbrushed on. In tests, even a layer as thin as just 62 nanometers – thousands of times thinner than a sheet of paper – could ...
- Cannibalistic materials feed on themselves to grow new nanostructureson September 4, 2018 at 12:49 am
The high-quality material used in these experiments was synthesised by Drexel University scientists, in the form of five-ply single-crystal mono-layer flakes of MXene. The flakes were taken from a ...
- Surface-agnostic highly stretchable and bendable conductive MXene multilayerson March 9, 2018 at 11:13 am
1B) or by spraying (Fig. 1C) of the two components onto glass. The color of the coating, which arises from the MXene nanosheets, became successively darker as the number of layer pairs or LbL cycles ...
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