Supercomputer helps to discover new carbon structures
26.01.2012
The objective of the doctoral dissertation of researcher Timo Vehviläinen was to find a way of storing explosive hydrogen in carbon nanostructures, but Vehviläinen ended up discovering new carbon structures.
During the last decade, the two carbon allotropes that we learnt at school, graphite and diamond, have been joined by several new carbon structures.
The football-shaped fullerene and graphene, a one-atom-thick sheet of carbon, have even brought Nobel prizes to their discoverers.
Researcher Timo Vehviläinen from Aalto University discovered several new carbon structures during his doctoral dissertation project with the help of computational methods.
Vehviläinen was especially interested in the smallest possible fullerene molecule, the spherical C20 composed of 20 carbon atoms. An important research question was whether structures based on this fullerene could be used for storing hydrogen.
- Some research papers suggest that as many as 60 hydrogen atoms could be stored inside a fullerene molecule, Vehviläinen says.
Hydrogen a possible replacement for fossil fuels
Carbon has a central role in the global energy supply since the majority of the world’s energy is produced by burning hydrocarbons. Hydrogen has been mentioned as a possible replacement for the diminishing supplies of fossil fuels, but producing and storing this explosive gas is a major problem.
- The safest option would be binding hydrogen to solids so that it could easily be released when necessary, Vehviläinen explains.
However, his simulations with fullerene and hydrogen revealed that fullerene binds hydrogen atoms slightly too tightly. Hydrogen atoms can be made to enter a fullerene sphere by exposing them to heat, but releasing the atoms from the fullerene molecule then becomes extremely difficult.
- If we had found a way of storing hydrogen, we would be very famous, Vehviläinen states realistically.
The researchers at Aalto University will continue their simulations, but instead of using hydrogen atoms, they will move on to using the hydrogen molecule H2 that is naturally found in the environment.
Although a scientific breakthrough was not made, a lot of new knowledge on the atom-level physics of carbon compounds was acquired.
- When a hydrogen atom attaches itself to a fullerene molecule, the molecule in some cases becomes magnetic. Currently, we do not know why this is.
The new carbon structures predicted by Vehviläinen form one of the most important results of the dissertation. One of these structures is quasi-graphene, a hybrid between carbon nanotubes and graphite.
- Its mechanical properties are similar to those of carbon nanotubes and its tensile strength is much greater than that of steel. In one direction it is soft like graphite, Vehviläinen describes the miraculous material. The electrical properties of quasi-graphene are also a mix between the properties of nanotubes and graphite.
- Certain directions of the structure are semiconducting and others conducting.
"It can be done"
Another interesting point concerning quasi-graphene is that it only exists in supercomputer forecasts. This does not bother the computational physicist. He believes that in ten years’ time synthesizing the material will no longer be a problem. The development of the field has been overwhelming.
- When I began my doctoral research project, synthesizing C20 fullerene was considered impossible. Now it can be done.
The tools of computational physicists consist of number-crunching supercomputers containing hundreds of processors. Everything starts with the basics of quantum mechanics, Schrödinger equation. Computer simulations show researchers what happens in matter on atom and electron level.
Among other things, Vehviläinen can predict the carbon atom to which a hydrogen atom will most likely attach itself in a fullerene molecule and what kind of a polymer structure will be formed when fullerene molecules are compressed under high pressure.
- We can also predict the properties of new carbon structures, such as how strong they are compared to diamond.
Currently, Vehviläinen is especially interested in three-dimensional fullerene polymers. He has a long list of possible applications:
- The storage of hydrogen, extremely durable materials, electronics components, quantum dots. Carbon is an extremely versatile material.
Timo Vehviläinen’s doctoral dissertation, "Hydrogen interaction with carbon nanostructures”, was presented for public examination and debate at the Aalto University School of Science on January 19, 2012.
The Aalto University Electronic Properties of Materials research group.
Further information:
Researcher Timo Vehviläinen
tel. +358 (0)40 753 8064
vehvilainen [at] iki [dot] fi
