Graphene foam sculpted for energy storage and sensors
Image credit: Rice University
Researchers based at Rice University in Texas have developed a method for sculpting conductive 3D objects with graphene foam, resulting in squishy-looking objects with many potential applications.
The project was carried out at the Tour Lab at Rice, which produced the world’s first laser-induced graphene in 2014. By burning plastic with a laser, it is possible to transform the surface of the plastic into interconnected flakes of graphene. This technique has been used for various 2D applications, including to create graphene cartoons on food.
Now, the researchers have extended their work in laser-induced graphene into the third dimension.
“We have built a prototype machine that lets us make graphene foam into 3D objects through automated successive layering and laser exposure,” said Professor James Tour. “This truly brings graphene into the third dimension without furnaces or the need for metal catalysts, and our process is easily scaled.”
This method is based upon laminated object manufacturing, whereby layers of a material are assembled first, then cut into shape. To create graphene objects, a surface layer of plastic is coated with ethylene glycol and turned to face its base to create a sandwich-like structure. Its uncoated top side is then heated with a laser to turn it into graphene, and the process is repeated with many layers until a structure has been formed.
Finally, the ethylene glycol and remaining plastic is removed by heating, leaving behind a pure, spongy block of graphene foam.
To demonstrate what could be achieved using this method, the Tour Group stacked five layers of graphene foam, then sculpted it into a custom shape using a fibre-lasing system on a 3D printer. They assembled lithium-ion capacitors – a safer alternative to lithium-ion batteries – using graphene foam as both anode and cathode. The capacity of the anode neared the theoretical limit of graphite and the capacity of the cathode exceeded typical capacities for carbon.
“This is excellent performance in these new-generation lithium-ion capacitors, which capture the best properties of lithium-ion batteries and capacitor hybrids,” said Tour.
Finally, the researchers soaked a block of graphene foam with liquid polydimethylsiloxane, which seeped through its nanopores; this resulted in a tough but still squishy material capable of conducting electricity. The group used this material to create a flexible sensor that could record pulse from the wrist and – with some further work – also measure blood pressure.