Hydrogen tanks for drives of the future

New extremely light polymer produced from organic building blocks

Lattice of a covalent organic compound (COF) University of Michigan
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Hydrogen is considered the fuel of the future. But to transport and store it lightweight, extremely stable materials are in demand. Now scientists have used the building blocks of ordinary plastic to construct new, particularly light and strong polymers that could be particularly suitable for hydrogen tanks. Their findings are reported in the current issue of the journal Science.

The trick to make the new materials, called covalent organic compounds (COF), was to get their building blocks to assemble into pre-determined, predictable crystal lattices. Adrien Côté, a researcher at the University of Michigan, explains: "Normal solid plastics are synthesized by rapid reactions that form the randomly arranged bonds of the polymers. As in much that goes really fast, it can degenerate into disorganization. "

Discovery of slowness

For this reason, the exact internal structures of such materials have often been studied and understood only partially. Determining or predicting their properties is therefore difficult. Côté and his colleagues now changed the reaction conditions to slow the entire polymerization process. The building blocks were able to crystallize in an organized way instead of neck-and-neck random ties.

After each new experiment, scientists analyzed the resulting polymers using X-ray crystallography and determined their bonding structure and properties. They use this information to continually change the reaction conditions until the polymers have the desired structure.

Lightweight elements in a sturdy grid

For his experiments, Côté teamed up with chemist Omar Yaghi, who has been working on a related group of materials known as organometallic compounds (MOF) for 15 years. At the molecular level, these consist of a framework of metal nodes with struts of organic materials. Depending on the metal and organic components, the angles of the struts can be selectively changed and thus also the properties of the material influence the display

In contrast to these "MOFs", the new covalent organic compounds contain no metals, but consist exclusively of very light elements such as hydrogen, boron, carbon, nitrogen and oxygen, which form strong covalent bonds with each other.

"Using lightweight elements allows us to produce very lightweight materials, " Côté explains. "This is especially important for the storage of hydrogen, because the lighter the material, the more economical it is to transport it in a vehicle. The strong covalent bonds also make the COFs a very robust material. "

Although the main goals of current research are the creation of new materials for the gas storage of fuel cells, C t, Yaghi and their colleagues are exploring variants of COFs suitable for electronic components or catalysts. "In our opinion, this is only the first step on the way to a very large and useful class of materials", says C t .

(University of Michigan, 18.11.2005 - NPO)