A conductive polymer (green) inside the small pores of a COF with a hexagonal framework (red and blue) work together to store electrical energy rapidly and efficiently. Image: William Dichtel, Northwestern University.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 driving range. Dichtel and his team report this new material in a paper in ACS Central Science.
An electric car currently relies on a complex interplay between batteries and supercapacitors to provide the energy it needs to go places, 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 rapidly, like a supercapacitor," said Dichtel, a pioneer in the young research field of covalent organic frameworks (COFs).
Dichtel and his research team have now combined a COF – a strong, stiff polymer with an abundance of tiny pores suitable for storing energy – with a very conductive material. In doing so, they have created the first modified redox-active COF that can compete with other older, porous carbon-based electrodes.
"COFs are beautiful structures with a lot of promise, but their conductivity is limited," Dichtel said. "That's the problem we are addressing here. By modifying them – by adding the attribute they lack – we can start to use COFs in a practical way." And modified COFs are commercially attractive: COFs are made from inexpensive, readily-available materials, while conventional carbon-based electrodes are expensive to process and mass-produce.
To demonstrate the new material's capabilities, the researchers built a coin-cell battery prototype device capable of powering a light-emitting diode for 30 seconds. This revealed that the material has outstanding stability, capable of 10,000 charge/discharge cycles. The researchers also performed extensive experiments to understand how the COF and the conducting polymer, called poly(3,4-ethylenedioxythiophene) (PEDOT), work together to store electrical energy.
Dichtel and his team synthesized the COF on an electrode surface. The two organic molecules that make up the COF self-assembled and condensed into a honeycomb-like grid, with individual two-dimensional layers stacked on top of the other. Into the grid's holes, or pores, the researchers deposited the conducting polymer.
Each pore is only 2.3nm wide, but the COF is full of these useful pores, creating a lot of surface area in a very small space. A small amount of the fluffy COF powder, just enough to fill a shot glass and weighing the same as a dollar bill, has the surface area of an Olympic swimming pool.
The modified COF showed a dramatic improvement in its ability to both store energy and to rapidly charge and discharge the prototype device. The material can store roughly 10 times more electrical energy than an unmodified COF, and can get electrical charge into and out of the device 10 to 15 times faster.
"It was pretty amazing to see this performance gain," Dichtel said. "This research will guide us as we investigate other modified COFs and work to find the best materials for creating new electrical energy storage devices."
This story is adapted from material from Northwestern University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.