Research led by the James M. Tour Group at Rice University, Texas, has developed an automated metal powder 3D printing method to make free-standing 3D graphene foams. The process allows for facile preparation of the material in bulk. This unlocks the potential to apply graphene’s unique properties to a range of objects including batteries and sound absorbers.
Pour some sugar on graphene
The process developed by the team at Rice, and respective collaborators at Tianjin University, the Tianjin Collaborative Innovation Center of Chemical Science, and Utah’s Qualified Rapid Products, uses a bed of sugar and powdered nickel (Ni) as the basis of this process.
After treatment inside a controlled-atmosphere chamber, the sugar/Ni powder is irradiated by a carbon-dioxide laser. This sinters a layer of graphene/Ni composite. Another layer of the sugar/Ni powder is then swept over the top, and sintering is repeated in consecutive layers to make a cube.
To remove the nickel content of the cube, the object is left to etch in an iron chloride solution for two days and purified in deionized water for 4 days. After this process, researchers are left with a fully-formed free standing cube of graphene foam, referred to as GF.
In characterization of the 3D printed GFs properties, the cubes proved to have relatively low electrical conductivity when compared to other 3D graphene structures. Dynamic mechanical analysis (DMA) of the GFs was undertaken in a course of 70,000 cycles. In this test “no collapse was detected, indicating a good structural stability of the 3D printed GFs.”
To improve the electrical conductivity and mechanical properties of the GFs, researchers propose the addition of carbon nanotubes as reinforcement. Previous research has shown that the so-named “rebar graphene” including nanotubes would be capable of retaining its shape and supporting 3,000 times its own weight.
The secret of 3D graphene
Adding three-dimensionality to an otherwise two-dimensional material is a key step toward full exploitation of graphene’s unique properties. Finding the best method of creating 3D graphene is one of the key areas in current materials research.
From a mathematical standpoint, a team at MIT has proposed a gyroid structure as the optimal 3D structure for graphene. Furthermore, one of the most effective methods of working with large quantities of the material to date is by producing graphene in its oxidised form.
Retaining high strength capabilities, graphene oxide (GO) has been added to a number of materials as a structural reinforcement, including medical applications in research from CWRU; and structural building blocks at the Harbin Institute of Technology and China’s Ministry of Education. Electrical conductivity of GO has also been harnessed to produce rechargeable batteries in research from Manchester Metropolitan University, the University of Chester, and Central South University.
Tour et al.’s research by comparison offers a way to work with graphene in its pure form, using nickel as only a supporting material. Further details of the process can be found in Three-Dimensional Printed Graphene Foams, a paper published online in the journal ACS Nano. The research is co-authored by Junwei Sha, Yilun Li, Rodrigo Villegas Salvatierra, Tuo Wang, Pei Dong, Yongsung Ji, Seoung-Ki Lee, Chenhao Zhang, Jibo Zhang, Robert H. Smith, Pulickel M. Ajayan, Jun Lou, Naiqin Zhao, and James M. Tour.
Featured image: A 3D printed cube of graphene foam and and SEM image of its molecular make-up, via ACS Nano