Shows new electrical energy storage materials

video: A Northwestern University chemist and his research team have developed a modified covalent organic structure (COF) material that can power a light emitting diode.
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Credit: American Chemical Society

A powerful new material developed by Northwestern University chemist William Dichtel and his research team could one day speed up the charging process of electric cars and help increase their range.

An electric car currently relies on a complex interplay of batteries and supercapacitors to provide the energy it needs to move, but that could change.

“Our material combines the best of both worlds: the ability to store large amounts of electrical energy or charge, like a battery, and the ability to charge and discharge quickly, like a supercapacitor,” said Dichtel, a pioneer in young research in the field of organic covalent frameworks (COF).

Dichtel and his research team combined a COF – a strong, rigid polymer with an abundance of tiny pores suitable for energy storage – with a highly conductive material to create the first redox-active modified COF that bridges the gap with others older porous. carbon-based electrodes.

“COFs are beautiful structures with a lot of promise, but their conductivity is limited,” said Dichtel. “That’s the problem we’re addressing here. By modifying them – adding the attribute they’re missing – we can start to use COFs in a practical way.”

And modified COFs are commercially attractive: COFs are made from inexpensive and readily available materials, while carbon-based materials are expensive to process and mass produce.

Dichtel, Robert L. Letsinger professor of chemistry at Weinberg College of Arts and Sciences, presents his team’s findings today (August 24) at the American Chemical Society (ACS) national meeting in Philadelphia. Also today, an article by Dichtel and co-authors from Northwestern and Cornell University was published by the journal ACS Central Science.

To demonstrate the capabilities of the new material, the researchers built a prototype button cell battery capable of powering a light-emitting diode for 30 seconds.

The material has exceptional stability, capable of 10,000 charge / discharge cycles, the researchers report. They also performed many additional experiments to understand how COF and the conductive polymer, called poly (3,4-ethylenedioxythiophene) or PEDOT, work together to store electrical energy.

Dichtel and his team fabricated the material on an electrode surface. Two organic molecules self-assembled and condensed into a honeycomb grid, a 2D layer stacked on top of each other. In the holes or pores of the grid, the researchers deposited the conductive polymer.

Each pore is only 2.3 nanometers wide, but the COF is filled with these useful pores, creating a large area in a very small space. A small amount of fluffy COF powder, just enough to fill a shot glass and weighing the same as a dollar bill, is on the surface of an Olympic swimming pool.

The modified COF showed a dramatic improvement in its ability to both store energy and quickly charge and discharge the device. The material can store about 10 times more electrical energy than unmodified COF, and it can move electrical charge in and out of the device 10 to 15 times faster.

“It was pretty amazing to see this performance gain,” said Dichtel. “This research will guide us as we study other modified COFs and work to find the best materials to create new electrical energy storage devices.”

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The research was conducted at Cornell University, where Dichtel was a faculty member until this summer, when he moved to Northwestern.

The article is titled “Superior charge storage and power density of a covalent organic framework modified by a conductive polymer”. In addition to Dichtel, other authors are Ryan P. Bisbey, of Northwestern; Catherine R. Mulzer (née DeBlase, first author), currently with Dow Electronic Materials; and Luxi Shen, James R. McKone, Na Zhang and Héctor D. Abruña, of Cornell.


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