Carbon has no peer as a conductive material in such a thin and robust form, especially in the form of graphene or certain types of nanotubes. Combining the two appears to offer great potential for electronic components like fast supercapacitors that, because of the massive surface area, may hold a great deal of energy in a tiny package.
Rice chemist Robert Hauge and his team made the first steps toward such a hybrid over the past decade. Hauge, a distinguished faculty fellow in chemistry at Rice and co-author of the new work, discovered a way to make densely packed carpets of nanotubes on a carbon substrate by suspending catalyst-laced flakes in a furnace. When heated, the catalyst built carbon nanotubes like skyscrapers, starting at the substrate and working their way up. In the process, they lifted the aluminum oxide buffer into the air. The whole thing looked like a kite with many strings and was dubbed an odako, like the giant Japanese kites.
In the new work, the team grew a specialized odako that retained the iron catalyst and aluminum oxide buffer but put them on top of a layer of graphene grown separately on a copper substrate. The copper stayed to serve as an excellent current collector for the three-dimensional hybrids that were grown within minutes to controllable lengths of up to 120 microns.
Electron microscope images showed the one-, two- and three-walled nanotubes firmly embedded in the graphene, and electrical testing showed no resistance to the flow of current at the junction.
"The performance we see in this study is as good as the best carbon-based supercapacitors that have ever been made," Tour said. "We're not really a supercapacitor lab, and still we were able to match the performance because of the quality of the electr
|Contact: David Ruth|