Graphene sheets are immensely strong, lightweight and excellent at conducting electricity. Theoretically, macroscopical three-dimensional graphene assemblies should retain the properties of nanoscale graphene flakes. However, recent attempts to make 3D graphene have resulted in weak conductivity due to poor contact between graphene sheets. Loss of strength is also a problem, and self-supporting 3D graphene has not yet been produced.
Inspired by the ancient food art of ‘blown sugar’, Bando and his team reasoned that the strutted, coherent nature of conjoined bubbles would lend itself to strength and conductivity if graphene could be structured in the same way. The researchers created a syrup of ordinary sugar and ammonium chloride. They heated the syrup, generating a glucose-based polymer called melanoidin, which was then blown into bubbles using gases released by the ammonium. The team found the best quality end-product resulted from a balance of equal ammonium decomposition and glucose polymerization during this stage.
As the bubbles grew, the remaining syrup drained out of the bubble walls, leaving within intersections of three bubbles. Under further heating, deoxidization and dehydrogenation, the melanoidin gradually graphitized to form ‘strutted graphene’: a coherent 3D structure made up of graphene membranes linked by graphene strut frameworks, which resulted from original bubble walls and intersectional skeletons respectively.
The bubble structure allows free movement of electrons throughout the network, meaning that the graphene retains full conductivity. Not only this, but the mechanical strength and elasticity of the 3D graphene is extraordinary robust– the team were able to compress it down to 80% of its original size with little loss of conductive properties or stability.
Following their discovery, Bando and his team reliably produced gram-level strutted 3D graphene with a cost $0.5 per gram