Graphene is a single layer of carbon atoms organized in a hexagonal lattice. When graphene sheets are neatly stacked on top of each other and formed into a three-dimensional shape, it becomes graphite, commonly known as the “lead” in pencils.
Because graphite is simply packed-together graphene, it has fairly poor mechanical properties. But if the graphene sheets are separated with air-filled pores, the three-dimensional structure can maintain its properties. This porous graphene structure is called a graphene aerogel.
3D-printed graphene objects
Exploiting graphene's exceptional electronic, mechanical, and thermal properties for practical devices requires fabrication techniques that allow the direct manipulation of graphene on micro- and macroscopic scales. The successful implementation of graphene-based devices invariably requires the precise patterning of graphene sheets at both the micrometer and nanometer scale.
Finding the ideal technique to achieve the desired graphene patterning remains a major challenge. It appears that 3D-printing techniques are an attractive fabrication route towards three-dimensional graphene structures. 3D -printing with graphene results in objects which unlock the ability to theoretically create any size or shape of graphene.
3D-printed graphene octet truss aerogel on strawberry blossom. (Image: Virginia Tech)
3D printed graphene objects are highly coveted in certain industries, including batteries, aerospace, separation, heat management, sensors, and catalysis.
There are different methods to build 3D graphene monoliths – for example freeze casting or emulsion templating, etc. – but they are limited to building simple shapes, for example cylinders or cubes.
A recently developed process to 3D-print graphene allows to design three-dimensional topology comprised of interconnected graphene sheets. This design and manufacturing freedom leads to optimization of strength, conductivity, mass transport, strength, and weight density that are not achievable in graphene aerogels.
3D Graphene for energy storage
The performance of batteries and supercapacitors depends on the density at which they can store energy and the speed at which they can be charged and discharged. Read more in our article on Graphene Nanotechnology in Energy.
These functions critically depend on the nanostructured electrodes that are used in these energy systems.
Porous carbon nanomaterials are widely employed as electrodes for supercapacitors and electrodes in commercial lithium ion batteries. Porous carbon, such as activated carbon, microporous carbon, and mesoporous carbon, usually has very high surface area and tunable porous structure but very poor electrical conductivity.
In contrast, graphene exhibits high electrical conductivity but limited surface area.
By fabricating a 3D porous graphene framework it becomes possible to build conductive scaffolds to host sulfur for lithium ion storage.
3D graphene for electronic and biomedical applications
Researchers have demonstrated that 3D printable graphene inks, like other conductive materials, could influence cell behavior, particularly those related to neurogenic stem cell lines. For instance, they show the ability of 3D-printed graphene ink scaffolds to induce neurogenic differentiation of adult mesenchymal stem cells without the need for any other neurogenic growth factors or external stimuli.
These results suggest that the unique physical, electrical, and biological properties of 3D-printed graphene inks could open the door to addressing a variety of medical problems requiring the regeneration of damaged, degenerated, or otherwise non-functional electrogenic tissues such as nerves, bone, or skeletal and cardiac muscle.