The Rice researchers recently demonstrated that even stronger superacids can separate graphite into sheets of graphene and bring them into solution. Unlike other methods involving chemical reactions that alter graphene, the superacid solution does not degrade the material’s properties. The group has used the solutions to make sheets of graphene with low electrical resistance and is now “full steam ahead” using these solutions to make graphene fibers, says Tour.
Tour expects the graphene processing method to have two major applications: transparent electrodes and structural materials. In both areas, it may bring down costs. Indium tin oxide, the transparent conducting material most commonly found in touch screens and solar cells, is expensive and brittle, says Benji Maruyama, senior materials research engineer at the Air Force Research Laboratory in Ohio. The U.S. Air Force is funding the Rice research. Many groups have demonstrated the advantages of graphene electrodes in terms of conductivity and flexibility; the Rice method should make it possible to manufacture them over large areas.
The process could also be used to bring down the costs of lightweight, tough structural materials made from carbon fiber. These materials have been around for decades, but they remain expensive because the processes used to manufacture them are complex and result in lost material. Instead of making pure carbon into fibers directly, as in the Rice process, the current process starts with a nitrile polymer fiber that’s heated to turn it into graphite. These fibers are then woven into mats and glued together to make a bulk material. “They’re used in aircraft, but not in automobiles, because the costs are too high,” says Tour. “If we can do this more cheaply and get as good or better properties, there is the potential for a real advance in carbon fibers.”