Other current attempts to make 3D graphene have produced weak conductivity because of poor contact between graphene sheets. Strength loss is also a problem, and this new method addresses this as well.
Taking their cue from the ancient food art of ‘blown sugar’, Yoshio Bando and his team believed that the strutted, coherent character of conjoined bubbles would contribute well to strength and conductivity if graphene could be structured in the same way.
The research team created a syrup of ordinary sugar and ammonium chloride. Then they heated the syrup, creating a glucose-based polymer called melanoidin.
The melanoidin was then blown into bubbles using gases released by the ammonium. The highest quality end-product came from a balance of equal ammonium decomposition and glucose polymerization during this stage.
As the bubbles formed, the remaining syrup drained out of the bubble walls, leaving within intersections of three bubbles.
When heated further, under 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.
Low cost plus High Scalability
Bando and his team were able to reliably produce strutted 3D graphene with a cost $0.5 per gram in their lab. The low-cost, high scalability of this new method may have many applications in engineering and electronics.
One application that was suggested was use as a highly effective supercapacitor. The material’s maximum-power-density is highest among 3D graphene-based aqueous super-capacitors, around 10^6 W/kg. This would provide for quick start-up of electric vehicles and launching of aircraft.