The team, led by Yun Hang Hu, the Charles and Carroll McArthur Professor of materials science and engineering at Michigan Tech, created a new way to synthesize sodium-embedded carbon nanowalls that previously were only theoretical.
Amorphous carbon has low conductivity but large surface area. Graphite, on the other hand, has high conductivity but low surface area. Three-dimensional graphene has the best of both properties--and the sodium-embedded carbon invented by Hu at Michigan Tech is even better.
"Sodium-embedded carbon's conductivity is two orders of magnitude larger than three-dimensional graphene," Hu says. "The nanowall structure, with all its channels and pores, also has a large accessible surface area comparable to graphene."
This is different from metal-doped carbon where metals are simply on the surface of carbon and are easily oxidized; embedding a metal in the actual carbon structure helps protect it. To make the material, Hu and his team had to create a new process. They used a temperature-controlled reaction between sodium metal and carbon monoxide to create a black carbon powder that trapped sodium atoms. Working with researchers at University of Michigan and University of Texas at Austin, they demonstrated that the sodium was embedded inside the carbon instead of adhered on the surface of the carbon. The team then tested the material in several energy devices.