Making graphene out of wood for degradable electronics
It seems like there's a new graphene breakthrough coming out of the James Tour lab at Rice University almost every month. Over the last few years, the researchers are responsible for developing a graphene-based de-icing coat for plane wings, a carbon material that can filter radionuclides out of water, and using graphene nanotubes to build better batteries. Now, the team has managed to make graphene out of wood, by blasting a piece of pine with a laser beam.
Normally graphene takes on a two-dimensional form, as a sheet of carbon just one atom thick. But it's not the most practical material to work with in that structure, so in 2014, the Rice researchers developed a way to make a 3D graphene foam by heating a polymer surface with a laser. They called the result laser-induced graphene (LIG) and have since found other uses for it, including turning it into a bacterial bug zapper.
The problem is, LIG could only be made using a specific plastic called polyimide. But the researchers found that some types of wood have a similar mechanical structure, thanks to an organic polymer called lignin. With a high level of lignin in its cells, pine was a particularly promising material, and it could prove to be a more practical source of graphene than polyimide.
"For some applications, such as three-dimensional graphene printing, polyimide may not be an ideal substrate," says Ruquan Ye, lead researcher on the study. "In addition, wood is abundant and renewable."
To make the graphene foam, the team heated a piece of pine with an industrial laser, inside a chamber with very specific conditions: it had normal room temperature and pressure, but an atmosphere of pure argon or hydrogen. The absence of oxygen is important, allowing the wood to be modified without burning. Much like the polyimide LIG, the surface of the wood flaked up into graphene foam, while still clinging to the block.
The team found that changing the intensity of the laser altered the chemical composition and thermal properties of the LIG. After some experimentation, it was found that 70 percent power was the optimal amount to produce the highest-quality graphene, which was dubbed pine laser-induced graphene (P-LIG).
The researchers then tested how well their new material could conduct electricity. They made electrodes by depositing layers of cobalt and phosphorus, or nickel and iron, on top of P-LIG, and found it was an effective electrocatalyst for splitting water into hydrogen and oxygen. Depositing polyaniline onto P-LIG instead made it a practical supercapacitor for storing energy. Down the track, the team believes wooden electronics could help curb the growing e-waste problem.
"Graphene is a thin sheet of a naturally occurring mineral, graphite, so we would be sending it back to the ground from which it came along with the wood platform instead of to a landfill full of electronics parts," says James Tour, lead scientist at the lab.
The research was published in the journal Advanced Materials.
Source: Rice University