DoE Finds New Way to Turn Waste Heat Into Energy for Portable Electronics, Wearables

The U.S. Department of Energy’s National Renewable Energy Laboratory has made advances in the thermoelectric performance of organic semiconductors that are based on single-walled carbon nanotube thin films.

Researchers at the Department of Energy (DoE) have made a breakthrough in harvesting thermoelectric energy using carbon nanotube thin films that could be used to power portable electronics and sensors for the Internet of Things (IoT) and wearable technology.

Scientists at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) have advanced the thermoelectric performance of organic semiconductors that are based on what are called single-walled carbon nanotube thin films (SWCNTs), they said. The films could be integrated into fabrics to convert waste heat into electricity or serve as a small power source.

Specifically, the team’s research demonstrated that there is potential to use SWCNTs as the primary material for efficient thermoelectric generators, rather than being used merely as a component in a “composite” thermoelectric material, according to researchers, who published a paper on their work in the journal Energy and Environmental Science.

Previously, research focused on using these tubes in composite thermo-electrical material comprised of, for example, carbon nanotubes and a polymer, said Jeffrey Blackburn, a senior scientist in NREL’s Chemical and Materials Science and Technology center and co-lead author of the paper with fellow senior scientist Andrew Ferguson.

Their recent work shows that scientists can forego using polymers or other materials and use the carbon nanotubes alone to create these generators, Blackburn said.

 

Scientists from the Department of Energy’s National Renewable Energy Laboratory (NREL) Andrew Ferguson, left, and Jeffrey Blackburn stand in front of a screen displaying single-walled carbon nanotubes. The research made a breakthrough in generating thermoelectric energy from thin films made from the tubes, which can be used for portable and wearable electronics. (Source: NREL)

 

“There are some inherent advantages to doing things this way,” he said. For instance, removing polymers from all SWCNT starting materials has shown to boost the thermoelectric performance and lead to improvements in how charge carriers move through the semiconductor, according to the paper.

Researchers also demonstrated in their work that the same SWCNT thin film achieved identical performance when doped with either positive or negative charge carriers. These carriers—two types of material called the p-type and the n-type legs—are necessary to generate sufficient power in a thermoelectric device.

On the contrary, semiconducting polymers—another organic thermoelectric material often used together with carbon to develop thermoelectric generators—typically produce n-type materials that perform much worse than their p-type counterparts, researchers found.

In their paper, Blackburn and Ferguson concluded that because SWCNT thin films can make p-type and n-type legs out of the same material with identical performance, the electrical current in each leg is inherently balanced. Used alone, then, SWCNT thin films should simplify the fabrication of a device, they said.

Further, the team found that the highest-performing materials had performance metrics that exceed current state-of-the-art solution-processed semiconducting polymer-organic thermoelectric materials.

“We could actually fabricate the device from a single material,” Ferguson said. “In traditional thermoelectric materials you have to take one piece that’s p-type and one piece that’s n-type and then assemble those into a device.”

Once developed, integrating these SWCNT into fabrics could serve a key function for “wearable” personal electronics by capturing body heat and converting it into electricity for power, Ferguson said.

 

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 15 years.

 

 

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