Researchers Increase Conductivity in 'Tinker Toy' Material

Drawing inspiration from a popular children's toy, researchers from Sandia National Laboratories have developed a new way to increase the electrical conductivity of metal-organic framework materials (MOFs).

MOF materials contain a crystalline structure made up of organic molecules linked together by metal ions. This combination of both inorganic and organic components results in a rare amalgamation of properties, including nanoporosity, ultrahigh surface areas and an impressive thermal stability.

"When you imagine the 'Tinker Toys' we played with as children, you recall they are essentially wooden balls with holes that you can link together with sticks," said Mark Allendorf, Sandia senior scientist. "MOFs work the same way, only you substitute metal ions for the balls and organic molecules for the sticks."

The new technique, which was able to increase the electrical conductivity of one MOF by more than six times, focused on filling the open space within the scaffolding with guest molecules to make the MOFs conduct electricity.

"Importantly, MOFs possess a characteristic of molecules that allows us to adapt their properties to a specific application: we can perform chemistry on them, unlike traditional inorganic electronic materials, such as silicon and copper," said Sandia researcher Alec Talin. "How you connect to molecules, where you place them - those issues have consistently perplexed materials scientists."

Published in the journal Science, the new approach circumvents this issue altogether by organizing the molecules using the MOFs' nanopores.

"The trick is to pick the right kind of molecule, so that it binds to and interacts with the entire framework," Talin said. Some MOFs have empty holes in the Tinker Toy-equivalent balls that are able to bind molecules that then infiltrate the pores, he explained.

Allendorf admits he had his doubts as they set about putting their hypothesis to the test.

"Frankly, I thought it would never work," he said.

As it turned out, the MOFs were conducting, though only slightly. Over time, however, the researchers were able to refine the process, with the final product proving to be more than 1 million times more conductive than what they started with, and 1,000 times more so than any other MFO previously reported.

"The overwhelming success of this project opens a whole new way to design electrically active materials," Talin said. "There are probably hundreds of potential applications for this work that come into play, such as breath analysis and microelectronics."