An atomically thin membrane with microscopically small holes may prove to be the basis for future hydrogen fuel cells, water filtering and desalination membranes, according to a group of 15 theorists and experimentalists, including three theoretical researchers from Penn State.
The team, led by Franz Geiger of Northwestern University, tested the possibility of using graphene, the robust single atomic layer carbon, as a separation membrane in water and found that naturally occurring defects, essentially a few missing carbon atoms, allowed hydrogen protons to cross the barrier at unprecedented speeds. While many researchers strive to make graphene defect-free to exploit its superior electronic properties, Geiger’s team found that graphene required the vacancies to create water channels through the membrane. Computer simulations carried out at Penn State and the University of Minnesota showed the protons were shuttled across the barrier via hydroxyl-terminated atomic defects, that is, by oxygen hydrogen groups linked at the defect.
“Our simulations and experiments showed that you need to have at least four carbon vacancies and some sort of channel to overcome the energy barrier that would normally prevent the protons from crossing to the other side,” says Adri van Duin, associate professor of mechanical and nuclear engineering, Penn State, who used reactive force-field calculations to do dynamical, atomistic scale simulations of the process. “If we can learn how to engineer the defects and the defect size, we could make an effective separation membrane. Although it still requires a lot of design work, clearly this looks highly attractive for many applications, including desalinization.”
It may also work for a new, less complicated design for fuel cells in the future, Geiger believes. “All you need is slightly imperfect single-layer graphene,” he says
Source: Penn State