Imagine clothing with the ability to self-regulate temperature. Or a more fuel-efficient, lower emissions car that can take waste heat and transform it into electricity. Thermoelectric (TE) materials transform “heat into useful electricity and vice versa,” making these types of applications possible.
In fact, in 2021, the global thermoelectric (TE) materials market topped $60 billion, and shows no signs of slowing. Traditional thermoelectric materials, however, are typically scarce, toxic, and lack flexibility. They have historically limited the scope of thermoelectric applications and the growth of the industry as a whole.
In this Nature Communications article, “Macroscopic weavable fibers of carbon nanotubes with giant thermoelectric power factor,” researchers found that carbon nanotube fibers (CNTF) could be a game changer. Carbon nanotube fibers have the potential to unlock thermoelectric applications across industries. Their combined electrical and thermal conductivity, alongside novel properties such as weavability and scalability, offer great promise for growth in thermoelectric textile applications.
Conventional TE materials limit thermoelectric applications
There are many applications for localized thermoelectric heating or cooling across aerospace, automotive, the medical industry - even simply keeping computer components cool.
However, it’s not just thermoelectric properties that come into consideration when choosing materials. Different applications have different performance prerequisites.
Consider industrial waste heat applications, or active cooling (where external devices improve heat transfer). These approaches are ideal for situations that require precise temperature control, or involve high heat loads. They typically require enhanced power factor (PF).
“The power factor tells you how much power density you can get out of a material upon certain temperature difference and temperature gradient,’ said Rice graduate student Natsumi Komatsu, lead author of the paper.”
Beyond the basic thermoelectric abilities, considerations such as toxicity, flexibility, and scalability come into play. The “conventional inorganic TE” materials, such as bismuth telluride, while possessing the basic desired TE properties, are not used widely due to “their toxicity, scarcity, and rigidity.” And their scarcity also renders this material costly.
Meanwhile, though “organic materials are safe, flexible, and inexpensive,” their power factor is small. These realities triggered the search for a new material that performed like inorganic TE materials.
Enter carbon nanotube fibers (CNTF).
Carbon nanotube fibers have thermoelectric advantages
CNT fibers possess the requisite thermoelectric properties for a host of exciting applications.
Recent advancements in “macroscopically ordered CNT assemblies” yielded “superb thermal and mechanical properties.” For these reasons, CNTs can be employed to create the ideal TE material that boasts high TE performance, as well as flexibility and scalability.
In fact, this study put these properties (weavability and scalability) to the test. The authors constructed a textile thermoelectric generator with CNT fibers, producing enough energy to power an LED. Their findings point to the promising role for CNT fibers in the development of future wearable and thermoelectric devices.
And on top of it all, CNTs are green, too. Matteo Pasquali, Professor of Chemical & Bio-molecular Engineering, Chemistry, and Materials Science at Rice University, and co-author of the study notes:
“Carbon nanotube fibers have been on a steady growth path and are proving advantageous in more and more applications. Rather than wasting carbon by burning it into carbon dioxide, we can fix it as useful materials that have further environmental benefits in electricity generation and transportation.”
Professor Pasquali is also DexMat Co-Founder and Chief Science Advisor. DexMat produces Galvorn, a conductive, super strong, super lightweight carbon nanomaterial.
Galvorn's CNT feedstock can be made from hydrocarbons: carbon is embodied in the form of CNTs, while co-producing clean hydrogen. In the future, Galvorn could even be made from captured carbon dioxide.
Carbon nanotube fibers (CNTF) beat incumbent thermoelectric materials
Researchers successfully produced ultrahigh-conductivity CNT fibers that featured a giant power factor: “... three times larger than that of Bi2Te3 [bismuth telluride], the commercially used inorganic TE material and…approaching the highest power factor (PF) achieved at room temperature by 2D materials: monolayer graphene.”
They found that the giant power factor was the result of the excellent morphology of the aligned CNT fibers, even when in a macroscopic assembly, which produced the ultrahigh power factor value. The high power factor is promising for active cooling applications thanks to the high thermal conductivity of the CNT fibers.
Using macroscopic weavable CNT threads, researchers then constructed a textile TE generator.
They found that CNT fiber's promise in the realm of fiber and textile electronics is great. Not only because they are weavable and able to be used with a commercial sewing machine but, unlike many alternative materials, they are washable, too.
Researchers also discovered that there was no loss in the device’s performance following repeated bending, confirming the flexibility of the textile TE generator and the materials used to construct it.
Carbon nanotube fiber can unlock thermoelectric textile applications
From aerospace to automotive to smart textiles, CNT fibers have the power to upend business as usual in the thermoelectric materials market. Broadening the scope of applications that can take of advantage of turning heat into useful electricity.
Learn more about Galvorn CNT fibers, yarns, and fabrics.