"In our one-step process, the interface is made with carbon-to-carbon bonding so it looks as if it's one single graphene sheet. That makes it an excellent thermal and electrical conductor in all planes."Liming Dai, Case Western Reserve University
An international team of scientists has developed what may be the first one-step process for making seamless carbon-based nanomaterials that possess superior thermal, electrical and mechanical properties in three dimensions.
These nanomaterials could potentially be used for increasing energy storage in high efficiency batteries and supercapacitors, enhancing the efficiency of energy conversion in solar cells and developing novel lightweight thermal coatings. They are described in a paper in Science Advances.
Carbon nanotubes can be highly conductive along their one-dimensional nanotube length, while the atom-thick sheets of carbon known as graphene are highly conductive in two dimensions. But this high conductivity disappears when these carbon nanomaterials are extended into the third dimension. This is because current two-step processes for stacking carbon nanotubes and graphene sheets on top of each other produce three dimensional (3D) materials that suffer from poor conductivity between the different layers.
"Two-step processes our lab and others developed earlier lack a seamless interface and, therefore, lack the conductance sought," explains Liming Dai, professor of macromolecular science and engineering at Case Western Reserve University and one of the leaders of the research. "In our one-step process, the interface is made with carbon-to-carbon bonding so it looks as if it's one single graphene sheet. That makes it an excellent thermal and electrical conductor in all planes."
To make the 3D material, the researchers etched radially-aligned nanoholes along the length and circumference of a tiny aluminum wire, then used chemical vapor deposition to cover the surface with carbon. This was all done without the need for a metal catalyst that could remain in the structure.
"Radially-aligned nanotubes grow in the holes,” says Zhong Lin Wang, professor of materials science and engineering at the Georgia Institute of Technology and the other leader of the research. “The graphene that sheathes the wire and nanotube arrays are covalently bonded, forming pure carbon-to-carbon nodal junctions that minimize thermal and electrical resistance.".
This architecture yields a huge surface area, adding to the transport properties, the researchers say. They calculate that the surface area of this architecture is nearly 527m2 per gram of material.
The properties of these 3D materials can also easily be customized. With the one-step process, the material can be made very long, or into a tube with a wider or narrower diameter, and the density of nanotubes can be varied to produce materials with differing properties for different needs.
As an initial demonstration of potential applications, a 3D supercapacitor made with uninterrupted fibers of carbon nanotubes and graphene matched or bettered – by a factor of four – the reported record-high capacities for this type of device. When used as an electrode in a dye-sensitized solar cell, the material enabled the cell to convert power with up to 6.8% efficiency and to achieve double the performance of an identical cell that used an expensive platinum wire electrode.
"The properties could be used for an even wider variety of applications, including sensitive sensors, wearable electronics, thermal management and multifunctional aerospace systems", said team member Ajit Roy, principal materials research engineer in the Materials and Manufacturing Directorate at the Air Force Research Laboratory in Dayton.
The scientists are continuing to explore the properties that can be derived from these single 3D graphene layer fibers and are also developing a process for making multilayer fibers.
This story is adapted from material from Case Western Reserve University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.